In the 21 first Century is electronic devices are changing the way humans interact with electronics machines for example: laptops, smartphones, internet, ROBOT, TV, video, organs, radio, electronic cars, and electronic instrumentation control equipment for aircraft and submarines as well as sophisticated weaponry weapons; so that a proposal is discussed how the equipment works so that it can be faster and more reliable and attractive to the environment in which electronic equipment works; one form of electronic circuits to improve the capabilities of electronic equipment is by displaying the description and the reality inside the electron bridge circuit passing through or setting up a complete and controlled electronic circuit .

e- Bridge in the field of electronic engineering and the more modern one is the international electronic communication network, namely INTERNET, so the bridge is defined as how an electron movement from a system is connected to other electron systems and integrated closed and open or better known as networking. in the field of electronics a series of application and interpretation of a bridge is to process the movement of electrons to be more flexible and safer in durability so that the appearance of actuators such as motors - LED lights as well as LED monitors and other electronic panel panel displays become more attractive and flexible also has memory and controlled data input speed; then many of us know in electronics various types of bridge circuits which function to control - setting and processing input data towards an accurate output display which may even be strengthened in the sense (e-DIREW [e-Data - Input - Read - Write] become e-REWIND [e-Read - Write - IN - Display] in electronic engineering the display can be in the form of stepper motors, DC, AC, Servo or Dynamo; The display can also be in the form of indicator lights such as LEDs (LED monitors), Speakers, Touch screens, DVD player printers and so on. Subsequent developments of electronic science were developed continuously by the United States government in the form of communication electronics, namely the creation of computer computers for large databases and memory as well as fast data access speeds - precisely and accurately, in the development of this electronic machine which is a combination from a series of electronic circuit components into integrated electronic circuits that are continuously integrated and developed to communicate all electronic equipment equipment to communicate with each other both individually, in groups, in groups and globally. Electronic technology that combines all equipment for electronic machine tools such as computers - laptops and smartphones as well as television and radio is possible by building larger bridges, namely INTERNET; where the bridge on the INTERNET is known as NETWORKING. in NETWORKING INTERNET there are so many concepts and forms of Bridge that of course every country uses a different Bridge concept in accordance with the ability to accept electronic technology and its ability to accommodate energy resources in the concept of capacity availability of electronic communication both electronic component resources - power source equipment for electronic machinery --- satellite capability resources as well as optical communication - and form contour areas of a country so that the flexibility of the electronic communication movement is in perfect efficiency. for this reason I will discuss here and I describe the e-Bridge Electronics condition that exists on earth for the present time, namely in the 21st century, which of course we as electronics experts always put forward the concept for the development of e-Bridge network, especially in my previous discussion Regarding the concept of 7 stages of electronic development, namely the 6th stage where the development of cables and wireless cables and materials for electron paths are better and more perfect so that the development of communication electronics can penetrate the 22nd century where stages 1 through stage 7 have been discussed in my previous book, it became more modern and the quality of reliable electronic technology and appearance.

                                                                           LOVE = Line On Victory Endless


                                                                    Hasil gambar untuk computer analysis for electron bridges in electronic circuits

Hasil gambar untuk computer analysis for electron bridges in electronic circuits

( ON / OFF Gen. Mac Tech __ e- Bridge )

Computation Structures

Digital systems are at the heart of the information age in which we live, allowing us to store, communicate and manipulate information quickly and reliably. This computer science course is a bottom-up exploration of the abstractions, principles, and techniques used in the design of digital and computer systems. If you have a rudimentary knowledge of electricity and some exposure to programming, roll up your sleeves, join in and design a computer system! We must to combine electronic interfaces between the physical world and digital devices . in the 21st century, one of the applications is the internet inside The Internet of Things (IoT) is expanding at a rapid rate, and it is becoming increasingly important for professionals to understand what it is, how it works, and how to harness its power to improve your business. We want to explore electronic circuit on analog and digital have to interact with the IoT bridge between the cyber- and physical worlds, in order to create efficiencies or solve business problems. We will look at IoT sensors, actuators and intermediary devices that connect things to the internet, as well as electronics and systems, both of which underpin how the Internet of Things works and what it is designed to do.

The concept of electronic bridges is as shown above

Lets"go to introduction electronic Bridge : Bridge in electronic means Complete electronic metering or Control Instrumentation electronic for reliable and appearance at electronic device performance .

XO___XO Different Types of Bridge Circuits and Circuit Diagrams

A bridge circuit is one kind of electrical circuit wherein the two branches of the circuit are linked to a third branch –which is connected in between the first two branches at some middle point along them. The bridge circuit was mainly designed for measurement purpose in the laboratory. And, one of the middle linking points is adjusted when it is used for a specific purpose. These circuits are used in linear, nonlinear, power conversion, instrumentation, filtering, etc.

The best known bridge circuit is the Wheatstone bridge; the term was invented by “Samuel Hunter Christie” and popularized by “Charles Wheatstone”. A bridge circuit is mainly used to measure resistance. This circuit is built with four resistors: R1, R2, R3 and RX; wherein the two resistors are with known values R1 & R3, one resistor’s resistance is to be concluded Rx, and one which is changeable and adjusted R2. Two opposite vertices are associated with a supply of electric current like a battery, and a galvanometer is connected across the additional two vertices. The variable resistor is familiarized until the galvanometer reads zero.

It is known that the relation between the variable resistor and its neighbor resistor R1 is equivalent to the relation between the unknown resistor and its neighbor R3, which permits the unknown value of the resistor to be calculated. The Wheatstone bridge circuit has also been widespread to calculate impedance in AC circuits, and also to calculate inductance, resistance, capacitance, and dissipation factor individually.

Different arrangements are identified as Wien bridge, Heaviside and Maxwell bridge. All the circuits are based on a similar concept, which is to contrast the o/p of two potentiometers sharing a frequent source.

Different Types of Bridge Circuit and Their Circuit Diagrams

Wheatstone bridge and Its Working

The term “Wheatstone bridge” is also called as Resistance Bridge that is, invented by “Charles Wheatstone”. This bridge circuit is used to calculate the unknown resistance values and as a means of regulating measuring instrument, ammeters, voltmeters, etc. But, the present digital millimeters offer the easiest way to calculate a resistance. In recent days, Wheatstone bridge is used in many applications such as; it can be used with modern op-amps to interface various sensors and transducers to amplifier circuits. This bridge circuit is constructed with two simple serial and parallel resistances in between a voltage supply terminal and ground terminals. When the bridge is balanced, then the ground terminal produces a zero voltage difference between the two parallel branches. A Wheatstone bridge consists of two i/p and two o/p terminals includes of four resistors arranged in a diamond shape.

Wheatstone Bridge and Its Working

A Wheatstone bridge is widely used to measure the electrical resistance. This circuit is built with two known resistors, one unknown resistor and one variable resistor connected in the form of bridge. When the variable resistor is adjusted, then the current in the galvanometer becomes zero, the ratio of two two unknown resistors is equal to the ratio of value of unknown resistance and adjusted value of variable resistance. By using a Wheatstone Bridge the unknown electrical resistance value can easily measure.

Wheatstone Bridge Circuit Arrangement

The circuit arrangement of the Wheatstone bridge is shown below. This circuit is designed with four arms, namely AB, BC, CD & AD and consists of electrical resistance P, Q, R and S. Among these four resistances, P and Q are known fixed electrical resistances. A galvanometer is connected between the B & D terminals via an S1 switch. The voltage source is connected to the A &C terminals via a switch S2. A variable resistor ‘S’ is connected between the terminals C & D. The potential at terminal D varies when the value of the variable resistor adjusts. For instance, currents I1 and I2 are flowing through the points ADC and ABC. When the resistance value of arm CD varies, then the I2 current will also vary.

If we tend to adjust the variable resistance one state of affairs could return once when the voltage drop across the resistor S that is I2.S becomes specifically capable to the voltage drop across resistor Q i.e I1.Q. Thus the potential of the point B becomes equal to the potential of the point D hence the potential difference b/n these two points is zero hence current through galvanometer is zero. Then the deflection in the galvanometer is zero when the S2 switch is closed.

Wheatstone Bridge Derivation

From the above circuit, currents I1 and I2 are

I1=V/P+Q and I2=V/R+S
Now potential of point B with respect to point C is the voltage drop across the Q transistor, then the equation is

                I1Q= VQ/P+Q …………………………..(1)
Potential of point D with respect to C is the voltage drop across the resistor S, then the equation is
                 I2S=VS/R+S …………………………..(2)
From the above equation 1 and 2 we get,
                                   VQ/P+Q = VS/R+S
`                                 Q/P+Q = S/R+S
                                     P+Q/Q=R+S/S
         P/Q+1=R/S+1

P/Q=R/S
R=SxP/Q
Here in the above equation, the value of P/Q and S are known, so R value can easily be determined.

The electrical resistances of Wheatstone bridge such as P and Q are made of definite ratio, they are 1:1; 10:1 (or) 100:1 known as ratio arms and the rheostat arm S is made always variable from 1-1,000 ohms or from 1-10,000 ohms

Example of Wheatstone Bridge

The following circuit is an unbalanced Wheatstone bridge, calculate the o/p voltage across C and D points and the value of the resistor R4 is required to balance the bridge circuit.

The first series arm in the above circuit is ACB
Vc= (R2/(R1+R2)) X Vs
R2=120ohms, R1=80 ohms, Vs=100
Substitute these values in the above equation
Vc= (120/(80+120)) X 100
= 60 volts
The second series arm in the above circuit is ADB

VD = R4/(R3+R4) X Vs

VD= 160/ (480+160) X 100
=25 Volts
The voltage across points C & D is given as
Vout= VC-VD
Vout= 60-25 = 35 volts.
The value of R4 resistor is required to balance the Wheatstone bridge bridge is given as:
R4= R2 R3/R1
120X480/ 80
720 ohms.

So, finally we can conclude that, the Wheatstone bridge has two i/p & two o/p terminals namely A & B, C& D. When the above circuit is balanced, the voltage across the o/p terminals is zero volts. When the Wheatstone bridge is unbalanced, the o/p voltage may be either +ve or –ve depending upon the unbalance direction.

Application of Wheatstone Bridge

The application of Wheatstone bridge is light detector using Wheatstone bridge circuit

Wheatstone Bridge Light Detector Circuit

Balanced bridge circuits are used in many electronic applications to measure changes in intensity of light, strain or pressure. The different types of resistive sensors which can be used in a Wheatstone bridge circuit include: potentiometers, LDR’s, strain gauges and thermistor’s, etc.

Wheatstone bridge applications are used to sense electrical and mechanical quantities. But, the simple Wheatstone bridge application is light measurement using photoresistive device. In the Wheatstone bridge circuit, a light dependent resistor is placed in the place of one of the resistors.

An LDR is a passive resistive sensor, that is used to convert the visible light levels into a change in resistance and later a voltage. LDR can be used to measure and monitor the light intensity level. LDR has a several Megha ohms resistance in dim or dark light around 900Ω at a 100 Lux of a light intensity and down to around 30ohms in a bright light. By connecting the light dependent resistor in the Wheatstone bridge circuit, we can measure and monitor the changes in the light levels.

The Wheatstone Bridge circuit is nothing more than two simple series-parallel arrangements of resistances connected between a voltage supply terminal and ground producing zero voltage difference between the two parallel branches when balanced. A Wheatstone bridge circuit has two input terminals and two output terminals consisting of four resistors configured in a diamond-like arrangement as shown. This is typical of how the Wheatstone bridge is drawn.

The Wheatstone Bridge

When balanced, the Wheatstone bridge can be analysed simply as two series strings in parallel. In our tutorial about Resistors in Series, we saw that each resistor within the series chain produces an IR drop, or voltage drop across itself as a consequence of the current flowing through it as defined by Ohms Law. Consider the series circuit below.

As the two resistors are in series, the same current ( i ) flows through both of them. Therefore the current flowing through these two resistors in series is given as: V/R_T.

I = V ÷ R = 12V ÷ (10Ω + 20Ω) = 0.4A

The voltage at point C, which is also the voltage drop across the lower resistor, R₂ is calculated as:

V_R2 = I × R₂ = 0.4A × 20Ω = 8 volts

Then we can see that the source voltage V_S is divided among the two series resistors in direct proportion to their resistances as V_R1 = 4V and V_R2 = 8V. This is the principle of voltage division, producing what is commonly called a potential divider circuit or voltage divider network.
Now if we add another series resistor circuit using the same resistor values in parallel with the first we would have the following circuit.

As the second series circuit has the same resistive values of the first, the voltage at point D, which is also the voltage drop across resistor, R₄ will be the same at 8 volts, with respect to zero (battery negative), as the voltage is common and the two resistive networks are the same.
But something else equally as important is that the voltage difference between point C and point D will be zero volts as both points are at the same value of 8 volts as: C = D = 8 volts, then the voltage difference is: 0 volts
When this happens, both sides of the parallel bridge network are said to be balanced because the voltage at point C is the same value as the voltage at point D with their difference being zero.
Now let’s consider what would happen if we reversed the position of the two resistors, R₃ and R₄ in the second parallel branch with respect to R₁ and R₂.

With resistors, R₃ and R₄ reversed, the same current flows through the series combination and the voltage at point D, which is also the voltage drop across resistor, R₄ will be:

V_R4 = 0.4A × 10Ω = 4 volts

Now with V_R4 having 4 volts dropped across it, the voltage difference between points C and D will be 4 volts as: C = 8 volts and D = 4 volts. Then the difference this time is: 8 – 4 = 4 volts
The result of swapping the two resistors is that both sides or “arms” of the parallel network are different as they produce different voltage drops. When this happens the parallel network is said to be unbalanced as the voltage at point C is at a different value to the voltage at point D.
Then we can see that the resistance ratio of these two parallel arms, ACB and ADB, results in a voltage difference between 0 volts (balanced) and the maximum supply voltage (unbalanced), and this is the basic principal of the Wheatstone Bridge Circuit.
So we can see that a Wheatstone bridge circuit can be used to compare an unknown resistance R_X with others of a known value, for example, R₁ and R₂, have fixed values, and R₃ could be variable. If we connected a voltmeter, ammeter or classically a galvanometer between points C and D, and then varied resistor, R₃ until the meters read zero, would result in the two arms being balanced and the value of R_X, (substituting R₄) known as shown.

Wheatstone Bridge Circuit

By replacing R₄ above with a resistance of known or unknown value in the sensing arm of the Wheatstone bridge corresponding to R_X and adjusting the opposing resistor, R₃ to “balance” the bridge network, will result in a zero voltage output. Then we can see that balance occurs when:

The Wheatstone Bridge equation required to give the value of the unknown resistance, R_X at balance is given as:

Where resistors, R₁ and R₂ are known or preset values.

Wheatstone Bridge Example No1

The following unbalanced Wheatstone Bridge is constructed. Calculate the output voltage across points C and D and the value of resistor R₄ required to balance the bridge circuit.

For the first series arm, ACB

For the second series arm, ADB

The voltage across points C-D is given as:

The value of resistor, R₄ required to balance the bridge is given as:

We have seen above that the Wheatstone Bridge has two input terminals (A-B) and two output terminals (C-D). When the bridge is balanced, the voltage across the output terminals is 0 volts. When the bridge is unbalanced, however, the output voltage may be either positive or negative depending upon the direction of unbalance.

Wheatstone Bridge Light Detector

Balanced bridge circuits find many useful electronics applications such as being used to measure changes in light intensity, pressure or strain. The types of resistive sensors that can be used within a wheatstone bridge circuit include: photoresistive sensors (LDR’s), positional sensors (potentiometers), piezoresistive sensors (strain gauges) and temperature sensors (thermistor’s), etc.
There are many wheatstone bridge applications for sensing a whole range of mechanical and electrical quantities, but one very simple wheatstone bridge application is in the measurement of light by using a photoresistive device. One of the resistors within the bridge network is replaced by a light dependent resistor, or LDR.
An LDR, also known as a cadmium-sulphide (Cds) photocell, is a passive resistive sensor which converts changes in visible light levels into a change in resistance and hence a voltage. Light dependent resistors can be used for monitoring and measuring the level of light intensity, or whether a light source is ON or OFF.
A typical Cadmium Sulphide (CdS) cell such as the ORP12 light dependent resistor typically has a resistance of about one Megaohm (MΩ) in dark or dim light, about 900Ω at a light intensity of 100 Lux (typical of a well lit room), down to about 30Ω in bright sunlight. Then as the light intensity increases the resistance reduces. By connecting a light dependant resistor to the Wheatstone bridge circuit above, we can monitor and measure any changes in the light levels as shown.

Wheatstone Bridge Light Detector

The LDR photocell is connected into the Wheatstone Bridge circuit as shown to produce a light sensitive switch that activates when the light level being sensed goes above or below the pre-set value determined by V_R1. In this example V_R1 either a 22k or 47kΩ potentiometer.
The op-amp is connected as a voltage comparator with the reference voltage V_D applied to the non-inverting pin. In this example, as both R₃ and R₄ are of the same 10kΩ value, the reference voltage set at point D will therefore be equal to half of Vcc. That is Vcc/2.
The potentiometer, V_R1 sets the trip point voltage V_C, applied to the inverting input and is set to the required nominal light level. The relay turns “ON” when the voltage at point C is less than the voltage at point D.
Adjusting V_R1 sets the voltage at point C to balance the bridge circuit at the required light level or intensity. The LDR can be any cadmium sulphide device that has a high impedance at low light levels and a low impedance at high light levels.
Note that the circuit can be used to act as a “light-activated” switching circuit or a “dark-activated” switching circuit simply by transposing the LDR and R₃ positions within the design.
The Wheatstone Bridge has many uses in electronic circuits other than comparing an unknown resistance with a known resistance. When used with Operational Amplifiers, the Wheatstone bridge circuit can be used to measure and amplify small changes in resistance, R_X due, for example, to changes in light intensity as we have seen above.
But the bridge circuit is also suitable for measuring the resistance change of other changing quantities, so by replacing the above photo-resistive LDR light sensor for a thermistor, pressure sensor, strain gauge, and other such transducers, as well as swapping the positions of the LDR and V_R1, we can use them in a variety of other Wheatstone bridge applications.
Also more than one resistive sensor can be used within the four arms (or branches) of the bridge formed by the resistors R₁ to R₄ to produce “full-bridge”, “half-bridge” or “quarter-bridge circuit arrangements providing thermal compensation or automatic balancing of the Wheatstone bridge.

The Wien Bridge Oscillator

The Wien Bridge Oscillator uses uses two RC networks connected together to produce a sinusoidal oscillator .
In the RC Oscillator tutorial we saw that a number of resistors and capacitors can be connected together with an inverting amplifier to produce an oscillating circuit.
One of the simplest sine wave oscillators which uses a RC network in place of the conventional LC tuned tank circuit to produce a sinusoidal output waveform, is called a Wien Bridge Oscillator.
The Wien Bridge Oscillator is so called because the circuit is based on a frequency-selective form of the Wheatstone bridge circuit. The Wien Bridge oscillator is a two-stage RC coupled amplifier circuit that has good stability at its resonant frequency, low distortion and is very easy to tune making it a popular circuit as an audio frequency oscillator but the phase shift of the output signal is considerably different from the previous phase shift RC Oscillator.
The Wien Bridge Oscillator uses a feedback circuit consisting of a series RC circuit connected with a parallel RC of the same component values producing a phase delay or phase advance circuit depending upon the frequency. At the resonant frequency ƒr the phase shift is 0^o. Consider the circuit below.

RC Phase Shift Network

The above RC network consists of a series RC circuit connected to a parallel RC forming basically a High Pass Filter connected to a Low Pass Filter producing a very selective second-order frequency dependant Band Pass Filter with a high Q factor at the selected frequency, ƒr.
At low frequencies the reactance of the series capacitor (C1) is very high so acts a bit like an open circuit, blocking any input signal at Vin resulting in virtually no output signal, Vout. Likewise, at high frequencies, the reactance of the parallel capacitor, (C2) becomes very low, so this parallel connected capacitor acts a bit like a short circuit across the output, so again there is no output signal.
So there must be a frequency point between these two extremes of C1 being open-circuited and C2 being short-circuited where the output voltage, V_OUT reaches its maximum value. The frequency value of the input waveform at which this happens is called the oscillators Resonant Frequency, (ƒr).
At this resonant frequency, the circuits reactance equals its resistance, that is: Xc = R, and the phase difference between the input and output equals zero degrees. The magnitude of the output voltage is therefore at its maximum and is equal to one third (1/3) of the input voltage as shown.

Oscillator Output Gain and Phase Shift

It can be seen that at very low frequencies the phase angle between the input and output signals is “Positive” (Phase Advanced), while at very high frequencies the phase angle becomes “Negative” (Phase Delay). In the middle of these two points the circuit is at its resonant frequency, (ƒr) with the two signals being “in-phase” or 0^o. We can therefore define this resonant frequency point with the following expression.

Wien Bridge Oscillator Frequency

Where:
ƒr is the Resonant Frequency in Hertz
R is the Resistance in Ohms
C is the Capacitance in Farads

We said previously that the magnitude of the output voltage, Vout from the RC network is at its maximum value and equal to one third (1/3) of the input voltage, Vin to allow for oscillations to occur. But why one third and not some other value. In order to understand why the output from the RC circuit above needs to be one-third, that is 0.333xVin, we have to consider the complex impedance (Z = R ± jX) of the two connected RC circuits.
We know from our AC Theory tutorials that the real part of the complex impedance is the resistance, R while the imaginary part is the reactance, X. As we are dealing with capacitors here, the reactance part will be capacitive reactance, Xc.

The RC Network

If we redraw the above RC network as shown, we can clearly see that it consists of two RC circuits connected together with the output taken from their junction. Resistor R₁ and capacitor C₁ form the top series network, while resistor R₂ and capacitor C₂ form the bottom parallel network.
Therefore the total DC impedance of the series combination (R₁C₁) we can call, Z_S and the total impedance of the parallel combination (R₂C₂) we can call, Z_P. As Z_S and Z_P are effectively connected together in series across the input, V_IN, they form a voltage divider network with the output taken from across Z_P as shown.
Lets assume then that the component values of R₁ and R₂ are the same at: 12kΩ, capacitors C₁ and C₂ are the same at: 3.9nF and the supply frequency, ƒ is 3.4kHz.

Series Circuit

The total impedance of the series combination with resistor, R₁ and capacitor, C₁ is simply:

We now know that with a supply frequency of 3.4kHz, the reactance of the capacitor is the same as the resistance of the resistor at 12kΩ. This then gives us an upper series impedance Z_S of 17kΩ.
For the lower parallel impedance Z_P, as the two components are in parallel, we have to treat this differently because the impedance of the parallel circuit is influenced by this parallel combination.

Parallel Circuit

The total impedance of the lower parallel combination with resistor, R₂ and capacitor, C₂ is given as:

At the supply frequency of 3400Hz, or 3.4kHz, the combined DC impedance of the RC parallel circuit becomes 6kΩ (R||Xc) with the vector sum of this parallel impedance being calculated as:

So we now have the value for the vector sum of the series impedance: 17kΩ, ( Z_S = 17kΩ ) and for the parallel impedance: 8.5kΩ, ( Z_P = 8.5kΩ ). Therefore the total output impedance, Zout of the voltage divider network at the given frequency is:

Then at the oscillation frequency, the magnitude of the output voltage, Vout will be equal to Zout x Vin which as shown is equal to one third (1/3) of the input voltage, Vin and it is this frequency selective RC network which forms the basis of the Wien Bridge Oscillator circuit.
If we now place this RC network across a non-inverting amplifier which has a gain of 1+R1/R2 the following basic Wien bridge oscillator circuit is produced.

Wien Bridge Oscillator

The output of the operational amplifier is fed back to both the inputs of the amplifier. One part of the feedback signal is connected to the inverting input terminal (negative or degenerative feedback) via the resistor divider network of R1 and R2 which allows the amplifiers voltage gain to be adjusted within narrow limits.
The other part, which forms the series and parallel combinations of R and C forms the feedback network and are fed back to the non-inverting input terminal (positive or regenerative feedback) via the RC Wien Bridge network and it is this positive feedback combination that gives rise to the oscillation.
The RC network is connected in the positive feedback path of the amplifier and has zero phase shift a just one frequency. Then at the selected resonant frequency, ( ƒr ) the voltages applied to the inverting and non-inverting inputs will be equal and “in-phase” so the positive feedback will cancel out the negative feedback signal causing the circuit to oscillate.
The voltage gain of the amplifier circuit MUST be equal too or greater than three “Gain = 3” for oscillations to start because as we have seen above, the input is 1/3 of the output. This value, ( Av ≥ 3 ) is set by the feedback resistor network, R1 and R2 and for a non-inverting amplifier this is given as the ratio 1+(R1/R2).
Also, due to the open-loop gain limitations of operational amplifiers, frequencies above 1MHz are unachievable without the use of special high frequency op-amps.

Wien Bridge Oscillator Example No1

Determine the maximum and minimum frequency of oscillations of a Wien Bridge Oscillator circuit having a resistor of 10kΩ and a variable capacitor of 1nF to 1000nF.
The frequency of oscillations for a Wien Bridge Oscillator is given as:

Wien Bridge Oscillator Lowest Frequency

Wien Bridge Oscillator Highest Frequency

Wien Bridge Oscillator Example No2

A Wien Bridge Oscillator circuit is required to generate a sinusoidal waveform of 5,200 Hertz (5.2kHz). Calculate the values of the frequency determining resistors R₁ and R₂ and the two capacitors C₁ and C₂ to produce the required frequency.
Also, if the oscillator circuit is based around a non-inverting operational amplifier configuration, determine the minimum values for the gain resistors to produce the required oscillations. Finally draw the resulting oscillator circuit.

The frequency of oscillations for the Wien Bridge Oscillator was given as 5200 Hertz. If resistors R₁ = R₂ and capacitors C₁ = C₂ and we assume a value for the feedback capacitors of 3.0nF, then the corresponding value of the feedback resistors is calculated as:

For sinusoidal oscillations to begin, the voltage gain of the Wien Bridge circuit must be equal too or greater than 3, ( Av ≥ 3 ). For a non-inverting op-amp configuration, this value is set by the feedback resistor network of R3 and R4 and is given as:

If we choose a value for resistor R3 of say, 100kΩ’s, then the value of resistor R4 is calculated as:

While a gain of 3 is the minimum value required to ensure oscillations, in reality a value a little higher than that is generally required. If we assume a gain value of 3.1 then resistor R4 is recalculated to give a value of 47kΩ. This gives the final Wien Bridge Oscillator circuit as:

Wien Bridge Oscillator Circuit Example No2

wien bridge oscillator circuit frequency

Wien Bridge Oscillator Summary

Then for oscillations to occur in a Wien Bridge Oscillator circuit the following conditions must apply.

With no input signal a Wien Bridge Oscillator produces continuous output oscillations.
The Wien Bridge Oscillator can produce a large range of frequencies.
The Voltage gain of the amplifier must be greater than 3.
The RC network can be used with a non-inverting amplifier.
The input resistance of the amplifier must be high compared to R so that the RC network is not overloaded and alter the required conditions.
The output resistance of the amplifier must be low so that the effect of external loading is minimized.
Some method of stabilizing the amplitude of the oscillations must be provided. If the voltage gain of the amplifier is too small the desired oscillation will decay and stop. If it is too large the output will saturate to the value of the supply rails and distort.
With amplitude stabilisation in the form of feedback diodes, oscillations from the Wien Bridge oscillator can continue indefinitely.

In The welcome to look at Oscillators, we will examine the Crystal Oscillator which uses a quartz crystal as its tank circuit to produce a high frequency and very stable sinusoidal waveform.

Maxwell’s Bridge

Definition: The bridge used for the measurement of self-inductance of the circuit is known as the Maxwell bridge. It is the advanced form of the Wheatstone bridge. The Maxwell bridge works on the principle of the comparison, i.e., the value of unknown inductance is determined by comparing it with the known value or standard value.

Types of Maxwell’s Bridge

Two methods are used for determining the self-inductance of the circuit. They are

Maxwell’s Inductance Bridge
Maxwell’s inductance Capacitance Bridge

Maxwell’s Inductance Bridge

In such type of bridges, the value of unknown resistance is determined by comparing it with the known value of the standard self-inductance. The connection diagram for the balance Maxwell bridge is shown in the figure below.

Let, L₁ – unknown inductance of resistance R₁.
L₂ – Variable inductance of fixed resistance r₁.
R₂ – variable resistance connected in series with inductor L₂.
R₃, R₄ – known non-inductance resistance
At balance,

The value of the R₃ and the R₄ resistance varies from 10 to 1000 ohms with the help of the resistance box. Sometimes for balancing the bridge, the additional resistance is also inserted into the circuit.
The phasor diagram of Maxwell’s inductance bridge is shown in the figure below.

Maxwell’s Inductance Capacitance Bridge In this type of bridges, the unknown resistance is measured with the help of the standard variable capacitance. The connection diagram of the Maxwell Bridge is shown in the figure below.

Let, L₁ – unknown inductance of resistance R₁.
R₁ – Variable inductance of fixed resistance r₁.
R₂, R₃, R₄ – variable resistance connected in series with inductor L₂.
C₄ – known non-inductance resistance
For balance condition,

By separating the real and imaginary equation we get,

The above equation shows that the bridges have two variables R₄ and C₄ which appear in one of the two equations and hence both the equations are independent.
The circuit quality factor is expressed as

Phasor diagram of Maxwell’s inductance capacitance bridge is shown in the figure below.

Advantages of the Maxwell’s Bridges

The following are the advantages of the Maxwell bridges

The balance equation of the circuit is free from frequency.
Both the balance equations are independent of each other.
The Maxwell’s inductor capacitance bridge is used for the measurement of the high range inductance.

Disadvantages of the Maxwell’s Bridge

The main disadvantages of the bridges are

The Maxwell inductor capacitance bridge requires a variable capacitor which is very expensive. Thus, sometimes the standard variable capacitor is used in the bridges.
The bridge is only used for the measurement of medium quality coils.

Because of the following disadvantages, the Hays bridge is used for the measurement of circuit inductance which is the advanced form of the Maxwell’s Bridge.

H-bridge paves new ways for LED lighting

The H-bridge is a classic circuit used for driving DC motors in a user-defined manner, such as in forward/reverse direction or PWM-assisted controlled RPM with the help of four discrete/integrated switches or electromechanical relays. It is widely employed in robotics and power electronics. This Design Idea is a novel implementation of this technique for driving white-LED arrays directly from the AC mains in full-wave current-limited mode to realize an excellent flicker-free, energy-efficient solid-state lamp. The circuit controls and maintains the LED excitation current in both negative and positive half cycles of the excitation voltage to a constant level by way of electronic switches operating alternately during the positive and negative excursion of the excitation voltage. This approach facilitates current-controlled rectification of AC voltage into a DC voltage for energizing series-connected LEDs with clean DC current with negligible ripple and substantially enhances the power factor.
As shown in Figure 1, transistors Q₁, Q₃, and Q₅ and diode D₄ as well as transistors Q₂, Q₄, and Q₆ and diode D₃ are configured as series-connected voltage-controlled current switches to form two arms of the H-bridge; diodes D₁ and D₂ form the other two arms of the bridge. The LED string is connected between the midpoints of the bridge designated as V_LED+ and V_LED GND, respectively. The AC is applied to the circuit through a current-limiting PTC resistor, R₅; series-connected capacitors, C₄ and C₅ (configured as a nonpolar capacitor, C_EFF); and inductor, L₁. Likewise, the neutral side of the mains is connected to the circuit ground through an inductor, L₂.

Figure 1 Current-limiting transistors and diodes route alternate AC half cycles to the series LED string.

During the positive half cycle, the AC power bus becomes positive with respect to the ground, and transistor Q₁ gets appropriate base bias through resistor R₁. Current flows through diode D₄, transistor Q₁, and resistor R₃, as illustrated by arrow A₁, and then through the LED string comprising 12 medium-power LEDs (LED₁ to LED₁₂) to the ground through diode D₂, as shown by arrow A₂. In a similar fashion, during the negative half cycle when the ac power bus becomes negative with respect to ground and transistor Q₂ gets base bias through resistor R₂, the current flows through diode D₃, transistor Q₂, and resistor R₄, as illustrated by arrow A₃, and then through the LED string to the ac power bus through diode D₁, as shown by arrow A₄. In this way, during a complete cycle the current flows through the string in the same direction and gets added up like you would get in a full-wave bridge rectifier. However, the magnitude of current I_LED remains constant as regulated by the respective switches serving as voltage-controlled current sources.
As the base emitter junctions of transistors Q₃ and Q₄ are connected across current-sensing resistors R₃ and R₄, respectively, they turn on when the voltage drop across R₃ and R₄ increases beyond Q₃ and Q₄’s base emitter voltages. At this point, Q₁’s and Q₂’s bases are pulled down, disrupting the flow of current through them during respective half cycles of the ac mains. In this way, the current flowing through the transistors is kept constant and never allowed to go beyond a threshold, set by appropriately choosing the R₃ and R₄ values. Q₅ and Q₆ limit the base current of Q₁ and Q₂ to a safe value (around 150 μA) to ensure that they are never overdriven. The substantial parts of the base currents of Q₁ and Q₂ are shunted to R₃ and R₄ by means of Q₅ and Q₆ when their respective base emitter voltages exceed the potential drop across R₆ and R₈ connected in series with R₁ and R₂, respectively.
The magnitude of ac current flowing into the bus is limited by the reactance of C_EFF(1/2πfC_EFF) at the mains frequency and can be altered by appropriately choosing C₄ and C₅, configured as a nonpolar capacitor. The circuit can also be driven by a resistive supply by replacing C_EFF with a suitable high-power resistor of 50 to 200Ω. This may facilitate an excellent power factor, but at the expense of very high power losses in the current-limiting resistor. R₃ and R₄ can be chosen appropriately as per the required constant-current magnitude. D₅ protects the LED string from high reverse voltage, and R₅ limits the inrush of current at turn-on. Inductors L₁ and L₂ and capacitor C₁ help in minimizing the EMI/RFI besides improving the power factor. A metal oxide varistor can also be inserted in parallel with the AC mains to protect the circuit from transients.

Figure 2 V_LED+ without capacitor C₂ has ripple (a); V_LED+ with capacitor C₂ has reduced ripple (b).

In the circuit, 12 0.5W LEDs operate at 120mA DC (135mA RMS) with respect to current-sensing resistors R₃ and R₄, chosen as 1Ω. You can, however, increase the number of LEDs to 18 as long as the voltage being applied across the string is more than the sum of the forward voltage of the individual LEDs. (White LEDs’ forward voltage varies from 3.3 to 4V.) The voltage appearing across the string is self-limiting (in this case, it is around 42V) and does not require any additional regulation, since series-connected LEDs behave like high-power zener diodes when operated in forward-biased mode. The circuit draws 11.5W power at 230VRMS and exhibits a power factor of 0.93 without any perceptible flicker in the LEDs. You may optionally connect a 220μF capacitor, C₂, between V_LED+ and V_LED GND to further suppress ripple, as shown in Figure 2. Alternatively, the given string can be replaced by six parallel-connected strings of LEDs, each having 12 to 18 20mA high-brightness LEDs. You must mount transistors Q₁ and Q₂ on heat sinks to avoid thermal runaway.

Fontana bridge

A Fontana bridge is a type of bridge circuit that implements a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops, implicit in this bridge configuration. This feature allows compensation for parasitic impedance

Z_{P}

connected in parallel with the useful load

Z_{S}

, which in turn keeps an excitation current

I_{S}

flowing through the useful load

Z_{S}

independent of the instantaneous value of

Z_{S}

. This feature is of great advantage for making electromechanical transducers.
If balance condition:

Z_{1}Z_{3}=Z_{P}Z_{2}

is met, then:

I_{S}=V_{IN}{\frac {Z_{P}+Z_{1}}{Z_{P}Z_{1}}}

The circuit includes two differential amplifiers. The top differential amplifier, whose output is referred to ground potential, has unitary gain. The bottom differential amplifier, whose output is referred to ground potential, has ideally infinite gain. Ordinary operational amplifiers can be adopted with limitations in accuracy and bandwidth. The Fontana bridge is also called Compensated Current Injection Circuit. It was originally discovered by Giorgio Fontana, University of Trento, Italy, in 2003 using a symbolic equation solver for kirchhoff's circuit laws. The bridge details are available in.

A Fontana bridge is a type of bridge circuit that implements a wide frequency band voltage-to-current converter. The converter is characterized by a combination of positive and negative feedback loops, implicit in this bridge configuration. This feature allows compensation for parasitic impedance

Z_((P))

connected in parallel with the useful load

Z_((S))

, which in turn keeps an excitation current

I_((S))

flowing through the useful load

Z_((S))

independent of the instantaneous value of

Z_((S))

. This feature is of great advantage for making electromechanical transducers.

If balance condition:

Z_((1))Z_((3))=Z_((P))Z_((2))

is met, then:

I_((S))=V_((IN)){\frac {Z_((P))+Z_((1))}{Z_((P))Z_((1))))

Fontana Bridge

Zobel networks are a type of filter section based on the image-impedance design principle. They are named after Otto Zobel of Bell Labs, who published a much-referenced paper on image filters in 1923.^[1] The distinguishing feature of Zobel networks is that the input impedance is fixed in the design independently of the transfer function. This characteristic is achieved at the expense of a much higher component count compared to other types of filter sections. The impedance would normally be specified to be constant and purely resistive. For this reason, Zobel networks are also known as constant resistance networks. However, any impedance achievable with discrete components is possible.

Zobel networks were formerly widely used in telecommunications to flatten and widen the frequency response of copper land lines, producing a higher-quality line from one originally intended for ordinary telephone use. However, as analogue technology has given way to digital, they are now little used.
When used to cancel out the reactive portion of loudspeaker impedance, the design is sometimes called a Boucherot cell. In this case, only half the network is implemented as fixed components, the other half being the real and imaginary components of the loudspeaker impedance. This network is more akin to the power factor correction circuits used in electrical power distribution, hence the association with Boucherot's name.
A common circuit form of Zobel networks is in the form of a bridged T. This term is often used to mean a Zobel network, sometimes incorrectly when the circuit implementation is, in fact, something other than a bridged T.

BBC engineers equalising audio landlines circa 1959. The boxes with two large black dials towards the top of the equipment racks are adjustable Zobel equalisers. They are used both for temporary outside broadcast lines and for checking the engineer's calculations prior to building permanent units

Parts of this article or section rely on the reader's knowledge of the complex impedance representation of capacitors and inductors and on knowledge of the frequency domain representation of signals.

Derivation

The basis of a Zobel network is a balanced bridge circuit as shown in the circuit to the right. The condition for balance is that;

{\frac {Z}{Z_{0))}={\frac {Z_{0)){Z'))

If this is expressed in terms of a normalised Z₀ = 1 as is conventionally done in filter tables, then the balance condition is simply;

Z={\frac {1}{Z'))

In other words,

\scriptstyle Z'

is simply the inverse, or dual impedance of

\scriptstyle Z

.
The bridging impedance Z_B is across the balance points and hence has no potential across it. Consequently, it will draw no current and its value makes no difference to the function of the circuit. However, its value is often chosen to be Z₀ for reasons which will become clear in the discussion of bridged T circuits.

Input impedance

The input impedance is given by

{\frac {1}{Z_((\text{in))))}={\frac {1}{Z_{0}+Z'))+{\frac {1}{Z+Z_{0))}

Substituting the balance condition,

Z'={\frac {Z_{0}^{2)){Z))

yields

Z_((\text{in))}=Z_{0}

The input impedance can be designed to be purely resistive by setting

Z_{0}=R_{0}\!\,

The input impedance will then be real and independent of ω in band and out of band no matter what complexity of filter section is chosen.

Transfer function

If the Z₀ in the bottom right of the bridge is taken to be the output load then a transfer function of V_in/V_o can be calculated for the section. Only the rhs branch needs to be considered in this calculation. The reason for this can be seen by considering that there is no current flow through R_B. None of the current flowing through the lhs branch is going to flow into the load. The lhs branch therefore, cannot possibly affect the output. It certainly affects the input impedance (and hence the input terminal voltage) but not the transfer function. The transfer function can now easily be seen to be;

A(\omega )={\frac {Z_{0)){Z+Z_{0))}

Bridged T implementation

The load impedance is actually the impedance of the following stage or of a transmission line and can sensibly be omitted from the circuit diagram. If we also set;

Z_{B}=Z_{0}\,\!

then the circuit to the right results. This is referred to as a bridged T circuit because the impedance Z is seen to "bridge" across the T section. The purpose of setting Z_B = Z₀ is to make the filter section symmetrical. This has the advantage that it will then present the same impedance, Z₀, at both the input and the output port.

Types of section

A Zobel filter section can be implemented for low-pass, high-pass, band-pass or band-stop. It is also possible to implement a flat frequency response attenuator. This last is of some importance for the practical filter sections described later.

Attenuator

Z and Z' for a Zobel attenuator

For an attenuator section, Z is simply

Z=R\,\!

and,

Z'=R'={\frac {R_{0}^{2)){R))

The attenuation of the section is given by;

L=20\log \left({\frac {R}{R_{0))}+1\right)\,{\text{dB))

Low pass

Z and Z ' for a Zobel low-pass filter section

For a low-pass filter section, Z is an inductor and Z ' is a capacitor;

Z=i\omega L\!\,

and

Z'={\frac {1}{i\omega C'))

where

C'={\frac {L}{R_{0}^{2))}

The transfer function of the section is given by

A(\omega )={\frac {R_{0)){i\omega L+R_{0))}

The 3 dB point occurs when ωL = R₀ so the 3 dB cut-off frequency is given by

\omega _{c}={\frac {R_{0)){L))

where ω is in the stop band well above ω_c,

A(\omega )\approx {\frac {R_{0)){i\omega L))

it can be seen from this that A(ω) is falling away in the stop band at the classic 6 dB/8ve (or 20 dB/decade).

High pass

Z and Z' for a Zobel high-pass filter section

For a high-pass filter section, Z is a capacitor and Z' is an inductor:

Z={\frac {1}{i\omega C))

and

Z'=i\omega L'\!\,

where

L'=CR_{0}^{2}\!\,

The transfer function of the section is given by

A(\omega )={\frac {i\omega CR_{0)){1+i\omega CR_{0))}

The 3 dB point occurs when ωC = ¹⁄_R₀ so the 3 dB cut-off frequency is given by

\omega _{c}={\frac {1}{CR_{0))}

In the stop band,

A(\omega )\approx i\omega CR_{0}

falling at 6 dB/8ve with decreasing frequency.

Band pass

Z and Z' for a Zobel band-pass filter section

For a band-pass filter section, Z is a series resonant circuit and Z' is a shunt resonant circuit;

Z=i\omega L+{\frac {1}{i\omega C))

and

Y'={\frac {1}{Z'))=i\omega C'+{\frac {1}{i\omega L'))

The transfer function of the section is given by

A(\omega )={\frac {i\omega CR_{0)){1+i\omega CR_{0}-\omega ^{2}LC))

The 3 dB point occurs when |1 − ω²LC| = ωCR₀ so the 3 dB cut-off frequencies are given by

\omega _{c}={\frac {1}{2LC))\left(\pm R_{0}C+{\sqrt {R_{0}^{2}C^{2}+4LC))\right)

from which the centre frequency, ω_m, and bandwidth, Δω, can be determined:

{\begin{aligned}\Delta \omega &={\frac {R_{0)){L))\\\omega _{m}&={\sqrt ((\frac {R_{0}^{2)){4L^{2))}+{\frac {1}{LC))))\end{aligned))

Note that this is different from the resonant frequency

\omega _{0}={\sqrt ((\frac {1}{LC))))

the relationship between them being given by

\omega _{m}^{2}=\left({\frac {\Delta \omega }{2))\right)^{2}+\omega _{0}^{2}

Band stop

Z and Z' for a Zobel band-stop filter section

For a band-stop filter section, Z is a shunt resonant circuit and Z' is a series resonant circuit:

Y={\frac {1}{Z))=i\omega C+{\frac {1}{i\omega L))

and

Z'=i\omega L'+{\frac {1}{i\omega C'))

The transfer function and bandwidth can be found by analogy with the band-pass section.

\Delta \omega ={\frac {1}{CR_{0))}

And,

\omega _{m}={\sqrt {\left({\frac {1}{2R_{0}C))\right)^{2}+{\frac {1}{LC))))

Practical sections

A transparent mask used to aid design of Zobel networks. The mask is laid over a plot of the line response and the component values corresponding to the closest fitting curve can be chosen. This particular mask is for high-pass sections.

Zobel networks are rarely used for traditional frequency filtering. Other filter types are significantly more efficient for this purpose. Where Zobels come into their own is in frequency equalisation applications, particularly on transmission lines. The difficulty with transmission lines is that the impedance of the line varies in a complex way across the band and is tedious to measure. For most filter types, this variation in impedance will cause a significant difference in response to the theoretical, and is mathematically difficult to compensate for, even assuming that the impedance is known precisely. If Zobel networks are used however, it is only necessary to measure the line response into a fixed resistive load and then design an equaliser to compensate it. It is entirely unnecessary to know anything at all about the line impedance as the Zobel network will present exactly the same impedance to line as the measuring instruments. Its response will therefore be precisely as theoretically predicted. This is a tremendous advantage where high quality lines with flat frequency responses are desired.

Basic loss

A practical high pass section incorporating basic loss used to correct high end roll-off

For audio lines, it is invariably necessary to combine L/C filter components with resistive attenuator components in the same filter section. The reason for this is that the usual design strategy is to require the section to attenuate all frequencies down to the level of the frequency in the passband with the lowest level. Without the resistor components, the filter, at least in theory, would increase attenuation without limit. The attenuation in the stop band of the filter (that is, the limiting maximum attenuation) is referred to as the "basic loss" of the section. In other words, the flat part of the band is attenuated by the basic loss down to the level of the falling part of the band which it is desired to equalise. The following discussion of practical sections relates in particular to audio transmission lines.

6 dB/octave roll-off

$High-pass Zobel network response for various basic losses. Normalised to R 0 = 1 {\displaystyle \scriptstyle R_{0}\;=\;1} and ω c = 1 {\displaystyle \scriptstyle \omega _{c}\;=\;1}$

High-pass Zobel network response for various basic losses. Normalised to

\scriptstyle R_{0}\;=\;1

and

\scriptstyle \omega _{c}\;=\;1

The most significant effect that needs to be compensated for is that at some cut-off frequency the line response starts to roll-off like a simple low-pass filter. The effective bandwidth of the line can be increased with a section that is a high-pass filter matching this roll-off, combined with an attenuator. In the flat part of the pass-band only the attenuator part of the filter section is significant. This is set at an attenuation equal to the level of the highest frequency of interest. All frequencies up to this point will then be equalised flat to an attenuated level. Above this point, the output of the filter will again start to roll-off.

Mismatched lines

Quite commonly in telecomms networks, a circuit is made up of two sections of line which do not have the same characteristic impedance. For instance 150 Ω and 300 Ω. One effect of this is that the roll-off can start at 6 dB/octave at an initial cut-off frequency

\scriptstyle f_((c1))

, but then at

\scriptstyle f_((c2))

can become suddenly steeper. This situation then requires (at least) two high-pass sections to compensate each operating at a different

\scriptstyle f_{c}

Bumps and dips

Bumps and dips in the passband can be compensated for with band-stop and band-pass sections respectively. Again, an attenuator element is also required, but usually rather smaller than that required for the roll-off. These anomalies in the pass-band can be caused by mismatched line segments as described above. Dips can also be caused by ground temperature variations.

Transformer roll-off

Low frequency equaliser section with compensation for inductor resistance. The resistance r represents the stray resistance of the non-ideal inductor. The resistance r' is a real resistor calculated to compensate for r.

Occasionally, a low-pass section is included to compensate for excessive line transformer roll-off at the low frequency end. However, this effect is usually very small compared to the other effects noted above.
Low frequency sections will usually have inductors of high values. Such inductors have many turns and consequently tend to have significant resistance. In order to keep the section constant resistance at the input, the dual branch of the bridge T must contain a dual of the stray resistance, that is, a resistor in parallel with the capacitor. Even with the compensation, the stray resistance still has the effect of inserting attenuation at low frequencies. This in turn has the effect of slightly reducing the amount of LF lift the section would otherwise have produced. The basic loss of the section can be increased by the same amount as the stray resistance is inserting and this will return the LF lift achieved to that designed for.
Compensation of inductor resistance is not such an issue at high frequencies were the inductors will tend to be smaller. In any case, for a high-pass section the inductor is in series with the basic loss resistor and the stray resistance can merely be subtracted from that resistor. On the other hand, the compensation technique may be required for resonant sections, especially a high Q resonator being used to lift a very narrow band. For these sections the value of inductors can also be large.

Temperature compensation

An adjustable attenuation high-pass filter can be used to compensate for changes in ground temperature. Ground temperature is very slow varying in comparison to surface temperature. Adjustments are usually only required 2-4 times per year for audio applications.

A collection of various designs of temperature compensation equaliser. Some can be adjusted with plugable links, others require soldering. Adjustment is not very frequent.

The internal components of a temperature equaliser. The inductor and capacitor on the right set the frequency at which the equaliser starts to operate, the banks of selectable resistors on the left set the basic loss and hence amount of equalisation.

Kelvin Bridge

The Kelvin bridge or Thompson bridge is used for measuring the unknown resistances having a value less than 1Ω. It is the modified form of the Wheatstone Bridge.

What is the need of Kelvin Bridge?

Wheatstone bridge use for measuring the resistance from a few ohms to several kilo-ohms. But error occurs in the result when it is used for measuring the low resistance. This is the reason because of which the Wheatstone bridge is modified, and the Kelvin bridge obtains. The Kelvin bridge is suitable for measuring the low resistance.

Modification of Wheatstone Bridge

In Wheatstone Bridge, while measuring the low-value resistance, the resistance of their lead and contacts increases the resistance of their total measured value. This can easily be understood with the help of the circuit diagram.

The r is the resistance of the contacts that connect the unknown resistance R to the standard resistance S. The ‘m’ and ‘n’ show the range between which the galvanometer is connected for obtaining a null point.
When the galvanometer is connected to point ‘m’, the lead resistance r is added to the standard resistance S. Thereby the very low indication obtains for unknown resistance R. And if the galvanometer is connected to point n then the r adds to the R, and hence the high value of unknown resistance is obtained. Thus, at point n and m either very high or very low value of unknown resistance is obtained.
So, instead of connecting the galvanometer from point, m and n we chose any intermediate point say d where the resistance of lead r is divided into two equal parts, i.e., r₁ and r₂

The presence of r₁ causes no error in the measurement of unknown resistance.

From equation (1), we get

The above equation shows that if the galvanometer connects at point d then the resistance of lead will not affect their results.
The above mention process is practically not possible to implement. For obtaining the desired result, the actual resistance of exact ratio connects between the point m and n and the galvanometer connects at the junction of the resistor.

Kelvin Double Bridge Circuit

The ratio of the arms p and q are used to connect the galvanometer at the right place between the point j and k. The j and k reduce the effect of connecting lead. The P and Q is the first ratio of the arm and p and q is the second arm ratio.

The galvanometer is connected between the arms p and q at a point d. The point d places at the centre of the resistance r between the point m and n for removing the effect of the connecting lead resistance which is placed between the unknown resistance R and standard resistance S.
The ratio of p/q is made equal to the P/Q. Under balance condition zero current flows through the galvanometer. The potential difference between the point a and b is equivalent to the voltage drop between the points E_amd.
Now,

For zero galvanometer deflection,

As we known, P/Q = p/q then above equation becomes

The above equation is the working equations of the Kelvins bridge. The equation shows that the result obtains from the Kelvin double bridge is free from the impact of the connecting lead resistance.
For obtaining the appropriate result, it is very essentials that the ratio of their arms is equal. The unequal arm ratio causes the error in the result. Also, the value of resistance r should be kept minimum for obtaining the exact result.
The thermo-electric EMF induces in the bridge during the reading. This effect can be reduced by measuring the resistance with the reverse battery connection. The real value of the resistance obtains by takings the means of the two.

Limitations of Kelvins Bridge

The sensitive galvanometer is used for detecting the balance condition.
The high measurement current is required for obtaining the good sensitivity.

Nowadays the kelvins bridge is replaced by the Kelvin Bridge Ohmmeter.

Campbell’s Bridge

The bridge which measures the unknown mutual inductance regarding mutual inductance such type of bridge is known as the Campbell bridge. The mutual inductance is the phenomenon in which the variation of current in one coil induces the current in the nearer coil. The bridge also used for measuring the frequency by adjusting the mutual inductance until the null point is not obtained.

Consider the figure below shows the mutual inductance.

Let, M₁ – unknown mutual inductance
L₁ – self-inductance of secondary of mutual inductance M₁
M₂ – variable standard mutual inductance
L₂ – self-inductance of secondary of mutual inductance M₂
R₁,R₂,R₃,R₄ – non-inductive resistance
The two steps are required for obtaining the balanced position of the bridge.
1. The detector is connected between points ‘b’ and, ‘d’. The circuit behaves like a simple self-inductance commercial bridge. The condition requires for obtaining the balanced position of a bridge is

The bridge is in balanced condition by adjustment the R₃ or R₄ and R₁ and R₂.
2. The detector is connected between the b’ and d’. Along with the step-1 adjustment if the mutual inductance M₂ is varied, then the balance point is obtained.

Anderson’s Bridge

The Anderson’s bridge gives the accurate measurement of self-inductance of the circuit. The bridge is the advanced form of Maxwell’s inductance capacitance bridge. In Anderson bridge, the unknown inductance is compared with the standard fixed capacitance which is connected between the two arms of the bridge.

Constructions of Anderson’s Bridge

The bridge has fours arms ab, bc, cd, and ad. The arm ab consists unknown inductance along with the resistance. And the other three arms consist the purely resistive arms connected in series with the circuit.

The static capacitor and the variable resistor are connected in series and placed in parallel with the cd arm. The voltage source is applied to the terminal a and c.

Phasor Diagram of Anderson’s Bridge

The phasor diagram of the Anderson bridge is shown in the figure below. The current I₁ and the E₃ are in phase and represented on the horizontal axis. When the bridge is in balance condition the voltage across the arm bc and ec are equal.

The current enters into the bridge is divided into the two parts I₁ and I₂. The I₁ is entered into the arm ab and causes the voltage drop I₁(R₁+R) which is in phase with the I₁. As the bridge is in the balanced condition, the same current is passed through the arms bc and ec.
The voltage drop E₄ is equal to the sum of the I_C/ωC and the I_Cr. The current I₄ and the voltage E₄ are in the same phase and representing on the same line of the phasor diagram. The sum of the current I_C and I₄ will give rise to the current I₂ in the arm ad.
When the bridge is at balance condition the emf across the arm ab and the point a, d and e are equal. The phasor sum of the voltage across the arms ac and de will give rise the voltage drops across the arm ab.
The V₁ is also obtained by adding the I₁(R₁+r₁) with the voltage drop ωI₁L₁ in the arm AB. The phasor sum of the E₁ and E₃ or E₂ and E₄ will give the supply voltage.

Theory of Anderson Bridge

Let, L₁ – unknown inductance having a resistance R₁.
R₂, R₃, R₄ – known non-inductive resistance
C₄ – standard capacitor

At balance Condition,

Now,

The other balance condition equation is expressed as

By substituting the value of I_c in the above equation we get,

and

on equating the equation, we get

Equating the real and the imaginary part, we get

Advantages of Anderson Bridge

The following are the advantages of the Anderson’s Bridge.

The balance point is easily obtained on the Anderson bridge as compared to Maxwell’s inductance capacitance bridge.
The bridge uses fixed capacitor because of which accurate reading is obtained.
The bridge measures the accurate capacitances in terms of inductances.

Disadvantages of Anderson Bridge

The main disadvantages of Anderson’s bridge are as follow.

The circuit has more arms which make it more complex as compared to Maxwell’s bridge. The equation of the bridge is also more complex.
The bridge has an additional junction which arises the difficulty in shielding the bridge.

Because of the above-mentioned disadvantages, Maxwell’s inductance capacitance bridge is used in the circuit.

Carey-Foster Slide-Wire Bridge

The Carey Foster Bridge is used for measuring the low resistance or for the comparison of two nearly equal resistances. The working principle of the Carey foster bridge is similar to the Wheatstone Bridge.

The circuit for the Carey foster bridge is shown in the figure below.

Let P, Q, R and S are the four resistors used in the bridge. The resistances of P and R are known while the R and S are the unknown resistors. The slide wire of length L is placed between the resistance R and S. The resistor P and Q are adjusted so that the ratio of P/Q is equivalent to the R/S. The ratio of the resistance is equivalent by sliding the contact on the sliding wiring.
Let l₁ is the distance from the left at which the balanced is obtained. Now the R and S are interchanged, and this time the balanced is obtained by sliding the contact at the distance of l₂.
Consider the equation for first balance

The r is the resistance per unit length of the sliding wire.
After interchanging the R and S, the balance equation of the bridge is

For the first balance equation

And for the second balance equation

From equation (1) and (2)

The difference between the resistance of S and R is obtained from a distance between the length of the slide-wire, i.e., l₁ – l₂ at balance condition.

Calibration of Slide Wire

The calibration of the sliding wire can be done by placing the resistance R or S in parallel with the slide wire of known resistance. Let S is known and S’ is its values when shunted by known resistance.

By solving the above equation, we get

By the help of the Carey foster bridge, the direct comparison between the resistance R and S regarding length can be done. The resistance of other components like the resistance of P, Q and sliding contact are completely eliminated.
Note: The special switch is used for interchanging the resistor S and R during the test.

AC Bridge

The bridge uses for measuring the value of unknown resistance, inductance and capacitance, is known as the AC Bridge. The AC bridges are very convenient and give the accurate result of the measurement.

The construction of the bridges is very simple. The bridge has four arms, one AC supply source and the balance detector. It works on the principle that the balance ratio of the impedances will give the balance condition to the circuit which is determined by the null detector.

General Equation for an AC Bridge

The bridges have four arms, two have non-inductive resistance and the other two have inductances with negligible resistance.
When the bridge is in a balanced condition,

The l₁ and R₁ are the unknown quantities which are measured in terms of R₂, R3, R₄ and L₂. From equation (1) and (2) the following points are concluded.

The two balance equation is always obtained from the AC bridges.
The unknown quantities are determined through the balanced equations. The unknown quantities are usually inductance, capacitance and resistance.
The balance equations are independent of frequency.

The ac bridges are also used in other applications likes in the communication system, in complex electronics circuit etc.

The Basic of ROBOTICS ::: Hybrid Stepper Motor

The word Hybrid means combination or mixture. The Hybrid Stepper Motor is a combination of the features of the Variable Reluctance Stepper Motor and Permanent Magnet Stepper Motor. In the center of the rotor, an axial permanent magnet is provided. It is magnetized to produce a pair of poles as North (N) and South (S) as shown in the figure below.

At both the end of the axial magnet the end caps are provided, which contains an equal number of teeth which are magnetized by the magnet. The figure of the cross section of the two end caps of the rotor is shown below.

The stator has 8 poles, each of which has one coil and S number of teeth. There are 40 poles on the stator, and each end cap has 50 teeth. As the stator and rotor teeth are 40 and 50 respectively, the step angle is expressed as shown below.

The rotor teeth are perfectly aligned with the stator teeth. The teeth of the two end caps are displaced from each other by half of the pole pitch. As the magnet is axially magnetized, all the teeth on the left and right end cap acquire polarity as south and north pole respectively.
The coils on poles 1, 3, 5 and 7 are connected in series to form phase A. Similarly, the coils on the poles 2, 4, 6 and 8 are connected in series to form phase B.
When Phase is excited by supplying a positive current, the stator poles 1 and 5 becomes South poles and stator pole 3 and 7 becomes north poles.
Now, when the Phase A is de-energized, and phase B is excited, the rotor will turn by a full step angle of 1.8⁰ in the anticlockwise direction. The phase A is now energized negatively; the rotor moves further by 1.8⁰ in the same anti-clockwise direction. Further rotation of the rotor requires phase B to be excited negatively.
Thus, to produce anticlockwise motion of the rotor the phases are energized in the following sequence +A, +B, -A, -B, +B, +A…….. For the clockwise rotation, the sequence is +A, -B, +B, +A……..
One of the main advantages of the Hybrid stepper motor is that, if the excitation of the motor is removed the rotor continues to remain locked in the same position as before the removal of the excitation. This is because of the Detent Torque produced by the permanent magnet.

Advantages of Hybrid Stepper Motor

The advantages of the Hybrid Stepper Motor are as follows:-

The length of the step is smaller.
It has greater torque.
Provides Detent Torque with the de-energized windings.
Higher efficiency at lower speed.
Lower stepping rate.

Disadvantages of Hybrid Stepper Motor

The Hybrid Stepper Motor has the following drawbacks.

Higher inertia.
The weight of the motor is more because of the presence of the rotor magnet.
If the magnetic strength is varied, the performance of the motor is effected.
The cost of the Hybrid motor is more as compared to the Variable Reluctance Motor.

Stepper Motor

The name Stepper Motor itself shows that the rotor movement is in the form of various steps or discrete steps. It is also known as Stepping Motor. The number of pulses fed into the controller circuit determines the angular rotation of the motor. Each input pulse produces one step of the angular movement. The drive is considered as an analog to digital converter. It has an inbuilt logic, which causes appropriate windings to be energised and de-energized by the solid state switches in the required sequence.
stepper-motor-fig

Contents:

There are three types of stepping motor based on the rotor arrangements. They are as follows:-

Variable Reluctance (VR) Stepper Motor

The variable reluctance motor is divided into two types. They are known as Single stack variable reluctance motor and Multi-stack variable reluctance motor.

Permanent Magnet (PM) Stepper Motor
Hybrid Stepper Motor (combination of VR and PM type)

Step Angle in Stepper Motor

Definition: Step angle is defined as the angle which the rotor of a stepper motor moves when one pulse is applied to the input of the stator.
The positioning of a motor is decided by the step angle and is expressed in degrees. The resolution or the step number of a motor is the number of steps it makes in one revolution of the rotor. Smaller the step angle higher the resolution of the positioning of the stepper motor.

The accuracy of positioning of the objects by the motor depends on the resolution. Higher the resolution greater will be the accuracy. Some precision motors can make 1000 steps in one revolution with a step angle of 0.36 degrees. A standard motor will have a step angle of 1.8 degrees with 200 steps per revolution. The various step angles like 90, 45 and 15 degrees are common in simple motors.
The number of phases can vary from two to six. Small steps angle can be obtained by using slotted pole pieces.

Advantages of Stepper Motor

The various benefits of the Stepping Motor are as follows:-

The motor is simple in construction, reliable.
At the standstill condition, the motor has full torque.
The motors are less costly.
They require little maintenance.
The stepper motor has an excellent and accurate starting, stopping and reversing response.

Disadvantages of Stepper Motor

The various disadvantages of the stepping motor are as follows:-

The motor uses more current as compared to the DC motor.
At the higher speed, the value of torque reduces.
Lower efficiency.
The Resonance condition arises and requires micro stepping.
At the high speed, the control is not possible.

Stepper Motor Applications

The Stepper motor is manufactured in various sizes ranging from milliwatts to hundreds of watts. Its maximum torque value ranges up to 15 Newton Meter and the step angle ranges from 1.8 to 90 degrees. As already discussed earlier about What is a Stepper Motor? and the Step Angle. The Stepper Motor Applications have a wide range. Some of the applications are given below.

As the stepper motor are digitally controlled using an input pulse, they are suitable for use with computer controlled systems.
They are used in numeric control of machine tools.
Used in tape drives, floppy disc drives, printers and electric watches.
The stepper motor also use in X-Y plotter and robotics.
It has wide application in textile industries and integrated circuit fabrications.
The other applications of the Stepper Motor are in spacecrafts launched for scientific explorations of the planets etc.
These motors also find a variety of commercial, medical and military applications and also used in the production of science fiction movies.
Stepper motors of microwatts are used in the wrist watches.
In the machine tool, the stepper motors with ratings of several tens of kilowatts is used

Advantages of Stepper Motor:

The rotation angle of the motor is proportional to the input pulse.
The motor has full torque at standstill.
Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3 – 5% of a step and this error is non cumulative from one step to the next.
Excellent response to starting, stopping and reversing.
Very reliable since there are no contact brushes in the motor. Therefore the life of the motor is simply dependant on the life of the bearing.
The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.
It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft.
A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses.

Applications:

Industrial Machines – Stepper motors are used in automotive gauges and machine tooling automated production equipments.
Security – new surveillance products for the security industry.
Medical – Stepper motors are used inside medical scanners, samplers, and also found inside digital dental photography, fluid pumps, respirators and blood analysis machinery.
Consumer Electronics – Stepper motors in cameras for automatic digital camera focus and zoom functions.

And also have business machines applications, computer peripherals applications.

Operation of Stepper Motor:

Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple toothed electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, for example a microcontroller.

To make the motor shaft turn, first one electromagnet is given power, which makes the gear’s teeth magnetically attracted to the electromagnet’s teeth. The point when the gear’s teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned ON and the first is turned OFF, the gear rotates slightly to align with the next one and from there the process is repeated. Each of those slight rotations is called a step, with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise. Stepper motor doesn’t rotate continuously, they rotate in steps. There are 4 coils with 90^o angle between each other fixed on the stator. The stepper motor connections are determined by the way the coils are interconnected.In stepper motor, the coils are not connected together. The motor has 90^o rotation step with the coils being energized in a cyclic order, determining the shaft rotation direction. The working of this motor is shown by operating the switch. The coils are activated in series in 1 sec intervals. The shaft rotates 90^o each time the next coil is activated. Its low speed torque will vary directly with current.

Stepper Motor Control by Varying Clock Pulses

Stepper motor control circuit is a simple and low-cost circuit, mainly used in low power applications. The circuit is shown in figure, which consist 555 timers IC as stable multi-vibrator. The frequency is calculated by using below given relationship:

Frequency = 1/T = 1.45/(RA + 2RB)C Where RA = RB = R2 = R3 = 4.7 kilo-ohm and C = C2 = 100 µF.

Stepper Motor Control by Varying Clock Pulses

The output of timer is used as clock for two 7474 dual ‘D’ flip-flops (U4 and U3) configured as a ring counter. When power is initially switched on, only the first flip-flop is set (i.e. Q output at pin 5 of U3 will be at logic ‘1’) and the other three flip-flops are reset (i.e. output of Q is at logic 0). On receipt of a clock pulse, the logic ‘1’ output of the first flip-flop gets shifted to the second flip-flop (pin 9 of U3). Thus logic 1 output keeps shifting in a circular manner with every clock pulse. Q outputs of all the four flip-flops are amplified by Darling-ton transistor arrays inside ULN2003 (U2) and connected to the stepper motor windings orange ,brown, yellow, black to 16, 15 ,14, 13 of ULN2003 and the red to +ve supply.

The common point of the winding is connected to +12V DC supply, which is also connected to pin 9 of ULN2003. The color code used for the windings is may vary form make to make. When the power is switched on, the control signal connected to SET pin of the first flip-flop and CLR pins of the other three flip-flops goes active ‘low’ (because of the power-on-reset circuit formed by R1-C1 combination) to set the first flip-flop and reset the remaining three flip-flops. On reset, Q1 of IC3 goes ‘high’ while all other Q outputs go ‘low’. External reset can be activated by pressing the reset switch. By pressing the reset switch, you can stop the stepper motor. The motor again starts rotating in the same direction by releasing the reset switch.

XO___XO +DW DW Electronic Bridges Information

Electronic bridges are used to cross from one circuit, channel, board, or element over to another. An electronic bridge is used to measure various parameters like:

inductance
capacitance
admittance
conductance
impedance

ypes

There are many types of electronic bridges. Examples include a Wheatstone circuit bridge, an H circuit bridge, and a network bridge.

Wheatstone circuit bridges are electrical bridge circuits that are used to measure resistance. Wheatstone circuit bridges consist of a common electric current source such as a battery and a galvanometer, which connects two parallel branches, containing four resistors and the values of three resistors are known.
An H circuit bridge has the capability to drive the motor forward or backward at any speed. An H circuit bridge can optionally use a completely independent power source.
A network bridge is an inexpensive method to connect LAN segments. Other electronic bridges are commonly available.

Features

There are several ways in which electronic bridges function. Electric bridges are employed for interfacing transducers and helping to measure impedance at high frequencies. Wheatstone circuit bridges are suitable for measuring any small change in resistance. Wheatstone circuit bridges consist of two parallel branches where one branch contains a known resistance and an unknown resistance, while the other parallel branch contains resistors of known values. This circuit measures the value of the unknown resistor by adjusting the values of the other three resistances until the current passing through the galvanometer decreases to zero. In an H circuit bridge, a condition called "shoot through" exists where there is a path between the positive and the negative sides of the H bridge that can make semiconductors ballistic. A network bridge is a type of electric bridge that connects two sides of adjacent networks. A network bridge is also called a network switch. Electronic bridges are designed and manufactured to meet most industry specifications.

Applications

Electronic bridges are used in many applications. Some examples include measurement of impedance, capacitance, conductance, and very high and very low resistance .

Basic Variable Speed Motor/Switch

We like to construct a simple set-up where I either turn the knob or move a lever varying degrees to get varying speeds from a low-powered rotary electric motor. The effect I desire is similar to a De Walt cordless drill (which I am personally very familiar with as a window and door installer). I would like the motor to operate at these somewhat precise varying speeds when I move the lever one way, but is it easy to then get it to reverse rotating direction with the same lever, with the same precision, or should I just incorporate another motor into this system? If you would answer this please understand that I am not an electrician or an electro-anything, and I only have the most basic understanding of these concepts, so please answer accordingly (condescension is ok). Figure 1 is the "lever switch". Figure 2 is the variable speed motor. Please don't mock my artwork.

Other bridge features also considered
Bridge sensitivity is an issue that must be considered when observing the bridge output. It is usually specified in mV/V, and is the value of bridge output when the bridge is excited with one volt and the sensor is at full scale. Typical sensitivity values are 1 to 2 mV/V. Accuracy of a standard bridge is usually between 0.1 and 1% before any calibration is performed.
Power dissipation is also an issue, as it is a function of bridge voltage and arm resistance. A higher excitation voltage produces a higher output, which is good, but results in higher dissipation. This dissipation affects low-power operation, obviously, but also induces increased self-heating of the bridge elements. Even though the bridge is self-compensating for temperature drift to a large extent, it can become a problem if the different elements are not thermally coupled and at the same temperature.
The output of the bridge is not grounded, so any conditioning/amplification circuitry must be isolated (Reference 2) or have a differential input. Also, some sensors perform better using AC rather than DC excitation, which can then be demodulated synchronously to eliminate second- and third-order errors. A bridge interface IC such as the AD7730 provides all necessary interface, amplification, scaling, calibration, and digital I/O along with easy-to-use, high-resolution performance. Image source: Analog Devices, Inc.
Due to the widespread use of bridge circuits and their many benefits, IC vendors have developed many specialized interface devices which simplify using them, setting amplifier gain, and minimizing various residual error sources. For example, the AD7730 from Analog Devices, Figure 4, can be configured for AC or DC excitation, provides a user-settable differential amplifier followed by 24-bit A/D conversion, and provides the resultant data in various serial formats to the system microcontroller. Despite its internal complexity, it provides an easy-to-use bridge excitation and interface function along with filtering, calibration, and many other user options.
The simple yet clever bridge topology has been a valuable configuration and tools since the earliest days of development of the principles of basic electrical circuits. Despite its age, it is very often still the best solution to the ongoing challenge of precisely matching a unknown component against a known one, or capturing small changes in a sensor output despite noise, component imperfections, and supply variations.

Implementing the Bridge Design with a Dual Op Amp
What if the amplifier used in Figure 4 needs only one power supply and is capable of outputting bipolar voltages? Some single-supply amplifiers need headroom above ground, but a device that provides a true-zero output may be a fit for bridge sensors (Figure 6). A possibly ideal dual op-amp for this application integrates charge-pump circuitry that generates the negative voltage rail in conjunction with external capacitors. This allows the amplifier to operate from a single +4.5 V to +15 V power supply, but it is as effective as a normal dual-rail ±4.5 V to ±15 V amplifier.

Figure 6. The MAX44267 precision, low-noise, low-drift, dual op amp offers a true-zero output from a single supply.
One such amplifier is the MAX44267, which can be implemented in the circuit of Figure 6 with just one supply voltage (positive supply, V_CC). The integrated negative V_SS generator or charge pump generates a negative supply voltage. This architecture provides an advantage to the designer, because it eliminates the need for negative supply regulators and reduces board layout space and cost.
Figure 7 includes a voltage reference to generate a 2.5 V_OUT reference. A dual op amp is used with the resistance bridge where R1 = R3 = 1 kW and R2 = R4 = 10 kW. An additional 1.8 kW is used in series to reduce the amount of current flowing through the bridge and to reduce power dissipation. The V(+) node becomes one-third the voltage reference’s output at a balanced condition. This is followed with second-stage amplification having a gain of 11 at the OUTA node.
Figure 7. The MAX44267 op amp operates from a single supply.
A Fluke RTD calibrator was used as the temperature-dependent resistance element (as PT1000) in place of R3; a temperature change from -50 C to +155 C is evaluated. For the given temperature change using a PT1000, the change in resistance(DR) is about 800 W and an equivalent range of 325 mV is effected (see Equation 4). Because amplifier 2 has an internal negative supply, it can accommodate this swing (-242mV to -83mV) at its input below ground, and it provides an output gain of 11.
Figure 7 utilizes a Sallen-Key filter in the second stage to filter the input signal to the required bandwidth (50Hz used in this case). Full-scale error accuracy within ±0.05% is obtained from the bridge output at node B without any calibration or trim. In this way the transfer function of the bridge circuit is made linear; improved performance of the front-end circuit is realized using MAX44267 in the subsequent section.
Test Measurements
1.Figure 8 shows the absolute bridge voltage output versus change in resistance (a linearity curve output), under 0.02%.

Figure 8.The transfer curve shows the absolute voltage output vs. temperature for the Figure 7 circuit.
2. Figure 9 shows the gain error plot as percentage versus full-scale. The error curve shows small wriggles, in order of 0.002%, that are a combination of manual data plotting and measurement setup noise.

Figure 9. Error % vs. full scale for the circuit in Figure 7.
3. Figure 10 shows the voltage noise density of the bridge plus amplifier: 115nV/ÖHz at 1kHz and 500nV/ÖHz under 50Hz. A 50 Hz filter was implemented in the second stage to remove the sensitivity to line noise.
Figure 10. Output noise density vs. frequency for the circuit in Figure 7.
4. Figure 11 shows the voltage noise(V_P-P) of the bridge plus amplifier, 0.1Hz to 10Hz, 6mV_P-P

Figure 11. Peak-to-peak voltage noise from 0.1Hz to 10Hz for the circuit in Figure 7.

A fragment of a computer motherboard with a north bridge and connectors

How to Build an H-bridge Circuit to Control 4 Motors

An H-bridge chip such as the L293/SN754410 can control up to 2 motors.

So in order to control 4 motors, we will need to use 2 H-bridge chips and tie them together.

We will build a circuit where all the motors are synchronized, meaning they act in symphony. Thus, if we input so that forward motion is activated, all the motors will spin in a forward direction. If we input reverse mode, all the motors will spin in reverse direction. So the motors act in concert.

This type of circuit is useful for any circuit that needs multiple motors. A common electronic device that now uses 4 DC motors are flying drones. If you go into amazon or any various online retailers to get a toy drone, the majority of them use 4 motors, the 4 of which act in concert. So this type of circuit has very valuable use in the real world.

In actuality, you could use how many motors you want. Since each H-bridge chip can operate 2 motors, then if you wanted to have 8 motors running, then you would need 4 H-bridge chips. If you want 16 motors running, then we need 8 H-bridge chips. You would just have to know how to connect them together, which is relatively simple. It's like just cascading them in a sequence.

But in this circuit, we do 4 motors.

The motor operation is

Components

2 L293/SN754410 H-bridge Chips
4 DC Motors
2 Pushbutton Switches
1 Toggle Switch
2 10KΩ resistors
Power Source

The L293/SN754410 H-bridge chip is 16-pin chip that can be used to drive and control inductive loads such as relays, solenoids, DC motors, and bipolar stepper motors.

In this circuit, we will be using it to control 2 DC motors.

The L293/SN754410 is a relatively inexpensive chip that can be obtained for a little over $1. One place that sells the L293 is Tayda Electronics- L293 Driver IC.

Before we build this circuit, you must understand the chip and all of its pin connections. You must always know pin connections when hooking up any chip.

Overall, the L293/SN754410 chips aren't very as complicated as they may seem. They both have identical pinouts.

The pinout of the L293/SN754410 is shown below.

L293 H bridge pinout

The L293/SN754410 is capable of controlling 2 motors.

It is a 4-channel H-bridge, meaning it can connect 4 terminal wires from motors. Since each motor has 2 terminals, it can control 2 motors (2x2=4).

Pin 1 is the enable pin for terminals 1 and 2. It enables motor to turn on when it is connected to a power. And disables the motor from functioning when connected to ground.

Pin 2 is the motor logic pin for terminal 1. This is the voltage level which one of the motor terminals receive. The logic level will determine what action the motor will take. This is one of the two logic levels that determines the function of the motor connected.

Pin 3 is the pin where we connect one of the terminals of the motor to.

Pin 4 and Pin 5 both get grounded.

Pin 6 is where we connect the other motor terminal to. This completes the 2-terminal connections necessary for a motor to be hooked up to the H-bridge IC.

Pin 7 is the motor logic pin for terminal 2. This is the second voltage signal we feed to the motor to determine the action the motor will take.

Pin 8 is the pin which receives the voltage needed to power on the motor. It is the motor power pin. This is the pin where we place the positive voltage of the power supply that will operate the DC motor. So if the motor is a 9V motor, then you will need to feed 9V into this pin. If the motor is a 12V motor, then you will need to feed 12V into this pin.

Pin 9 is the enable pin for terminals 3 and 4. It enables the motor to turn on when connected to power and disables the motor when connected to ground.

Pin 10 is the motor logic pin for terminal 3. This is one of the logic voltage signals that determines the action that the second motor will take.

Pin 11 is the pin where we connect one of the terminals of the second motor to.

Pin 12 and Pin 13 both get grounded.

Pin 14 is the pin where we connect the other terminal of the second motor to.

Pin 15 is the motor logic pin for terminal 4. It is the second voltage signal that we feed into the second motor to determine the action the motor will take.

Pin 16 is the pin which receives the voltage needed for power for the IC. It is the IC power pin. The IC needs just about 5V in order to operate. Therefore, we feed 5V into this pin.

These are all the pins of the motor. Once power is supplied to the IC and the motor and all the terminals of the motor are connected, then the pins which determine how the motors will operate are the logic levels that we feed into it.

The logic levels determine what action the motor will take.

A breakdown of logic levels and the resultant motor action are shown in the table below.

Enable	Logic Pin 1	Logic Pin 2	Result
High	Low	High	Forward
High	High	Low	Reverse
High	Low	Low	Stop
High	High	High	Stop
Low	Doesn't matter	Doesn't matter	Off

When the enable pin is high and the motor is fed a LOW voltage signal at the first pushbutton and a HIGH voltage signal at the second pushbutton, then the motors will spin forward. When the enable is high and the motor is fed a HIGH voltage signal at the first pushbutton and a LOW voltage signal at the second pushbutton, then the motors will spin in reverse. And with both logic levels at the same level (2 HIGHs or 2 LOWs), then the motors will stop spinning.

4-Motor H-bridge Circuit

The H bridge circuit we will build to control 4 motors is shown below.

This above circuit built on a breadboard is shown below.

4-motor H-bridge circuit breadboard schematic

How this circuit works is based on the 2 switches that control the logic state and the 1 enable switch.

All the motor logic pins are tied together for each of the motors, so the 2 pushbuttons control the logic state for all the 4 motors. Thus, this is why they act in concert. So the first pushbutton controls the first logic state for each of the motors. And the second pushbutton controls the second logic state of each of the motors.

So with the motor logic pins normally LOW, if we press down on the second button while leaving the first one unpressed, then the motors will spin in a forward.

Now if we press down on the first pushbutton while leaving the second one unpressed, the motors will spin in the reverse direction.

If we leave both unpressed or press down on both simultaneously, the motors will not spin.

And this is all that is necessary for the operation of our 4-motor device.

To wire it up, it's pretty simple. For each chip, we connect terminals 1 and 3 and then connect terminals 2 and 4. This way, both motors of a chip are synched in together in a given chip. After this, for each additional chip we do the same, and then tie in the the logic pins of the chip before into the chip after, so that all logic pins are connected together.

How to Build an H bridge Circuit with Transistors

In this circuit, we will show how to build an H-bridge circuit with transistors.

An h bridge is a circuit that is used primarily to control motors; they allow for forward and reverse motion of the motors. Therefore, the motor can be utilized with its full bidirectional capability.

To build an H-bridge, the only option is not to use an IC chip for an H-bridge. You can also build it with discrete and simple components such as with transistors and resistors.

Even though it's almost invariably simpler to use an IC to act as an H-bridge such as the popular L293 IC, there may be times you may want to design one yourself for any various reasons. You may also just be interested in knowning how an h bridge works.

So in this circuit, we will build an H-bridge simply with bipolar junction transistors.

Since motors run off a good amount of current, we will use high-current gain and high-power transistors. These are transistors provide very good current gain and transistors that deal with a lot of power.

In total, we use 4 different transistors, 2 PNP transistors and 2 NPN transistors.

The 2 types of transistors we will use are the TIP107 PNP transistors and the TIP102 NPN transistors. These are darlington transistors that can deal with high power outputs. Again, since motors require a good amount of current, normally about 75mA or so, we want a high-power transistor. Motors require several times more current than an output device that say an LED would. We will talk about these transistors more.

Know that h bridges are useful for circuits that require bidirectional functioning. Otherwise, the only way to be able to operate the device bidirectionally would be to manually switch the polarity leads of the device. An H-bridge eliminates this need.

So, again, h bridges can be used for any type of bidirectional 2-lead device that works in opposite directional depending on which lead is connected to power. It's mostly for motors, but it can also be for other devices as well.

Components

2 TIP107/127 PNP transistors
2 TIP102/120 NPN transistors
4 1KΩ resistors
2 5.6KΩ resistors
DC motor

Really any NPN transistors or PNP transistors can be used. But it is better for them to be high-power transistors, since motors need adequate current.

The TIP107/127 transistors are PNP darlington transistors.

Being that they are a darlington transistors, they provide high current gain. They also can deal with high power. The collector of the TIP107 transistor can deal with up to 80 watts of power, while the TIP127 can deal with up to 65W.

Being that the highest-rated DC motors are normally 12V, this means that the collector can pass 6.7A. Obviously, the motor requires nothing close to this. We need less than 100mA. So this transistor is well above the same range in power that we need.

The datasheets for the TIP107 or the TIP127 can be found at the following links: TIP107 PNP Datasheet and TIP127 PNP Datasheet.

The TIP102/TIP120 transistors are NPN darlington transistors.

Being darlington transistors, they also provide high current gain. This is good so that they can drive a high-power device such as a motor. The transistors themselves can deal with high power.

The datasheets for the TIP102 or the TIP120 can be found at the following links: TIP102 NPN Datasheet and TIP120 NPN Datasheet.

Again, you can really use any NPN or PNP transistors. High-power ones are better for this circuit, as motors need more, but you can mix and match and see what works.

The DC motor can be any type, of really any voltage. We are using a 6-12V DC power supply, so the maximum rating the motor should have is 12V. Normally, anyway, DC motors aren't rated higher than 12V, so you can use practically any motor.

Besides these, all we need else are resistors.

H Bridge Circuit Built with Transistors

So the first thing that should be done is setting up power for the circuit. The circuit operates off of 6-12V, so it can run any type of motor. However, if you are using a much lower voltage-rated DC motor such as a 3V, you can use lower voltage.

The circuit is manually controlled through a single pole double throw (SPDT) switch, a toggle switch.

The positive voltage either powers the base of the transistor on the left or the right. This transistor that gets the positive voltage turns on.

This turns on the transistor on top on the other side.

Thus, if we turn on the left transistor, current flows from the right of the power source through the transistor on the top right, through the DC motor from right to left, and then from the left transistor to ground.

If we flip the toggle switch to the other side, the bottom right transistor will be powered on. This turns on the transistor at the top on the left side. Current flows from the power source, through the leftmost transistor at the top, through the DC motor, from left to right, and through the rightmost transistor and down to ground.

Therefore, the circuit functions as an H-bridge.

If the switch is flipped one way, the motor spins in one direction.

If the switch is flipped the other way, the motor spins in the other direction.

So the circuit is able to achieve bidirectionality of the motor, as an h bridge should.

Normally, we would put diodes in reverse biased across the transistors. These diodes would help dampen transient spikes that are generated by the motor's coils so that they do not damage other components in the circuits. When a transistor stops running, it can create reverse emf, transient voltage spikes that can be large. To prevent them, reverse biased diodes would stop these spikes from proceeding to other parts of the circuit, where they could cause damage. Being we're flipping the transistors on and off by flipping the toggle switch, you do want to have protection against back emf.

A SPDT switch is used for manual control to demonstrate how the circuit works. It is perfect because it only allows one of the NPN transistors to be on at any given time. Both transistors cannot be on at the same time because both transistors would have current flowing through, which is like a forbidden state. Therefore, it should be avoided. A SPDT switch avoids this condition.

The circuit, as is, will never be off unless the power supply is removed, being that the SPDT has no switch in which both transistors are grounded. To counter this, you could add a switch to the power supply so that the power supply disconnects from the circuit, if this is desired.

If you don't want the circuit to be manually controlled by a switch, you can remove the SPDT switch and instead connect the base of the NPN transistors to whatever device you want to control it, such as a microcontroller. You still keep the 1KΩ resistors at the base.

Another thing is that this circuit, as if, puts the DC motor at one speed. To vary the speeds, instead of inputting a fixed DC voltage to the base of the transistors, a pulse width modulated signal would be applied to the base. We won't get into this article what value of PWM signal you would need to achieve a given speed, but you can take this approach to vary the speed of the DC motor. This is a far more efficient way than using a potentiometer to vary the speed, which is inefficient since it creates large power waste, though you can still use it.

So this is how an h bridge circuit can be built with transistors.

XO__XO +DW DW SAW Different Networking Devices And Hardware Types — Hub, Switch, Router, Modem, Bridge, Repeater

Short Bytes: Different networking devices have different roles to play in a computer network. These network devices also work at different segments of a computer network performing different works. In our new series after network topology, we talk about different networking devices like a switch, router, hub, bridge etc.

Computer networking devices are known by different names such as networking devices, networking hardware, network equipment etc. However, all of the names mean the same but have got different purposes. After covering different topics on network topologies and their advantages and disadvantages, we are here once again with a series on the network devices.
Before we talk more about the networking devices, here are a few topics you might want to take a look at that we covered under network topology section:

If we take a look at the different devices, they work at different layers of the computer networks. Different layers of a computer network are like different zones of a computer network with specified works, also called as ‘network protocols’.
For example:
A LAN cable has got the purpose of connecting a computer to the local area network, a Wi-Fi router has got the purpose of sending and receiving data between you and your internet connection. Similarly, we can think of other network devices with different purposes to serve.

Different networking devices:

Network Hub:

Network Hub is a networking device which is used to connect multiple network hosts. A network hub is also used to do data transfer. The data is transferred in terms of packets on a computer network. So when a host sends a data packet to a network hub, the hub copies the data packet to all of its ports connected to. Like this, all the ports know about the data and the port for whom the packet is intended, claims the packet.
However, because of its working mechanism, a hub is not so secure and safe. Moreover, copying the data packets on all the interfaces or ports makes it slower and more congested which led to the use of network switch.

Network Switch:

Like a hub, a switch also works at the layer of LAN (Local Area Network) but you can say that a switch is more intelligent than a hub. While hub just does the work of data forwarding, a switch does ‘filter and forwarding’ which is a more intelligent way of dealing with the data packets.

So, when a packet is received at one of the interfaces of the switch, it filters the packet and sends only to the interface of the intended receiver. For this purpose, a switch also maintains a CAM (Content Addressable Memory) table and has its own system configuration and memory. CAM table is also called as forwarding table or forwarding information base (FIB).

Modem:

A Modem is somewhat a more interesting network device in our daily life. So if you have noticed around, you get an internet connection through a wire (there are different types of wires) to your house. This wire is used to carry our internet data outside to the internet world.
However, our computer generates binary data or digital data in forms of 1s and 0s and on the other hand, a wire carries an analog signal and that’s where a modem comes in.
A modem stands for (Modulator+Demodulator). That means it modulates and demodulates the signal between the digital data of a computer and the analog signal of a telephone line.

Network Router:

A router is a network device which is responsible for routing traffic from one to another network. These two networks could be a private company network to a public network. You can think of a router as a traffic police who directs different network traffic to different directions.

Bridge:

If a router connects two different types of networks, then a bridge connects two subnetworks as a part of the same network. You can think of two different labs or two different floors connected by a bridge.

Repeater:

A repeater is an electronic device that amplifies the signal it receives. In other terms, you can think of repeater as a device which receives a signal and retransmits it at a higher level or higher power so that the signal can cover longer distances.
For example, inside a college campus, the hostels might be far away from the main college where the ISP line comes in. If the college authority wants to pull a wire in between the hostels and main campus, they will have to use repeaters if the distance is much because different types of cables have limitations in terms of the distances they can carry the data for.
When these network devices take a particular configurational shape on a network, their configuration gets a particular name and the whole formation is called Network topology. In certain circumstances when we add some more network devices to a network topology, its called Daisy chaining.

Bridging (networking)

A network bridge is a computer networking device that creates a single aggregate network from multiple communication networks or network segments. This function is called network bridging. Bridging is distinct from routing. Routing allows multiple networks to communicate independently and yet remain separate, whereas bridging connects two separate networks as if they were a single network. In the OSI model, bridging is performed in the data link layer (layer 2). If one or more segments of the bridged network are wireless, the device is known as a wireless bridge and the function as wireless bridging.
There are four types of network bridging technologies: simple bridging, multiport bridging, learning or transparent bridging, and source route bridging .

A high-level overview of network bridging, using the ISO/OSI layers and terminology

Transparent bridging

Transparent bridging uses a table called the forwarding information base to control the forwarding of frames between network segments. The table starts empty and entries are added as the bridge receives frames. If a destination address entry is not found in the table, the frame is flooded to all other ports of the bridge, flooding the frame to all segments except the one from which it was received. By means of these flooded frames, a host on the destination network will respond and a forwarding database entry will be created. Both source and destination addresses are used in this process: source addresses are recorded in entries in the table, while destination addresses are looked up in the table and matched to the proper segment to send the frame to. Digital Equipment Corporation (DEC) originally developed the technology in the 1980s.
In the context of a two-port bridge, one can think of the forwarding information base as a filtering database. A bridge reads a frame's destination address and decides to either forward or filter. If the bridge determines that the destination host is on another segment on the network, it forwards the frame to that segment. If the destination address belongs to the same segment as the source address, the bridge filters the frame, preventing it from reaching the other network where it is not needed.
Transparent bridging can also operate over devices with more than two ports. As an example, consider a bridge connected to three hosts, A, B, and C. The bridge has three ports. A is connected to bridge port 1, B is connected to bridge port 2, C is connected to bridge port 3. A sends a frame addressed to B to the bridge. The bridge examines the source address of the frame and creates an address and port number entry for A in its forwarding table. The bridge examines the destination address of the frame and does not find it in its forwarding table so it floods it to all other ports: 2 and 3. The frame is received by hosts B and C. Host C examines the destination address and ignores the frame. Host B recognizes a destination address match and generates a response to A. On the return path, the bridge adds an address and port number entry for B to its forwarding table. The bridge already has A's address in its forwarding table so it forwards the response only to port 1. Host C or any other hosts on port 3 are not burdened with the response. Two-way communication is now possible between A and B without any further flooding in network.

Simple bridging

A simple bridge connects two network segments, typically by operating transparently and deciding on a frame-by-frame basis whether or not to forward from one network to the other. A store and forward technique is typically used so, during forwarding, the frame integrity is verified on the source network and CSMA/CD delays are accommodated on the destination network. In contrast to repeaters which simply extend the maximum span of a segment, bridges only forward frames that are required to cross the bridge. Additionally, bridges reduce collisions by partitioning the collision domain.

Multiport bridging

A multiport bridge connects multiple networks and operates transparently to decide on a frame-by-frame basis whether and where to forward traffic. Like the simple bridge, a multiport bridge typically uses store and forward operation. The multiport bridge function serves as the basis for network switches.

Implementation

The forwarding information base stored in content-addressable memory (CAM) is initially empty. For each received ethernet frame the switch learns from the frames source MAC address and adds this together with the ingress interface to build the forwarding information base. The switch then forwards the frame to the interface found in the CAM based on the frames destination MAC address. If the destination address is unknown the switch sends the frame out on all interfaces (except ingress interface). This behaviour is called unicast flooding.

Forwarding

Once a bridge learns the addresses of its connected nodes, it forwards data link layer frames using a layer 2 forwarding method. There are four forwarding methods a bridge can use, of which the second through fourth methods were performance-increasing methods when used on "switch" products with the same input and output port bandwidths:

Store and forward: the switch buffers and verifies each frame before forwarding it; a frame is received in its entirety before it is forwarded.
Cut through: the switch starts forwarding after the frame's destination address is received. There is no error checking with this method. When the outgoing port is busy at the time, the switch falls back to store-and-forward operation. Also, when the egress port is running at a faster data rate than the ingress port, store-and-forward is usually used.
Fragment free: a method that attempts to retain the benefits of both store and forward and cut through. Fragment free checks the first 64 bytes of the frame, where addressing information is stored. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded. This way the frame will always reach its intended destination. Error checking of the actual data in the packet is left for the end device.
Adaptive switching: a method of automatically selecting between the other three modes .

Audio Video Bridging

Audio Video Bridging (AVB) is a common name for the set of technical standards developed by the Institute of Electrical and Electronics Engineers (IEEE) Audio Video Bridging Task Group of the IEEE 802.1 standards committee. This task group was renamed to Time-Sensitive Networking Task Group in November 2012 to reflect the expanded scope of work.
The charter of this organization is to "provide the specifications that will allow time-synchronized low latency streaming services through IEEE 802 networks". These consist of:

IEEE 802.1BA: Audio Video Bridging (AVB) Systems;
IEEE 802.1AS: Timing and Synchronization for Time-Sensitive Applications (gPTP);
IEEE 802.1Qat: Stream Reservation Protocol (SRP); and
IEEE 802.1Qav: Forwarding and Queuing for Time-Sensitive Streams (FQTSS).

IEEE 802.1Qat and 802.1Qav are amendments to the base IEEE 802.1Q document, which specifies the operation of "Media Access Control (MAC) Bridges and Virtual Bridged Local Area Networks", which are implemented by network devices typically called Ethernet switches.
To help ensure interoperability between devices that implement the AVB standards, the AVnu Alliance develops device certification for the automotive, consumer, and professional audio and video markets .

Background

Audio and video (AV) equipment connections historically were analog one-way, single-purpose and point-to-point. Even digital AV standards often were point-to-point and one-way such as S/PDIF for audio and the serial digital interface (SDI) for video. This connection model resulted in large confusing masses of cables, especially in professional and high-end consumer applications.

Wiring of a patch bay of an outside broadcasting van

Attempts to get around these problems included new technologies such as IEEE 1394 (known as FireWire), and adaptations of standard computer network technologies such as Audio over Ethernet or Audio over IP. Specialized professional, home, and automotive protocols did not interoperate. Adapting standard networks could use commodity technology, but tight quality of service control was difficult.

Benefits

Some benefits of AVB systems are:

Improved synchronization
Low-latency
Reliability
No infrastructure requirements
Networked Live Sound

Requirements

Requirements included synchronizing multiple streams to ensure they can be rendered correctly in time; a simple example of this is lip synch. For more stringent applications, such as keeping multiple digital speakers properly in phase within a professional environment, synchronization within 1μs is needed. Worst case delay, including source and destination buffering, must be low and deterministic. For example, consumer user-interface responses of about 50ms, or about 2ms for live performances. Applications must be able to reserve network resources, sometimes called admission control. AVB is also considered for industrial control applications.

IEEE standardization

In July 2004, the IEEE 802.3 started a residential Ethernet study group for A/V streaming. In November 2005, work moved to the IEEE 802.1 working group, responsible for cross-network bridging standards. In particular, the group wanted the technology to be scalable from inexpensive consumer applications to professional standards.

Summary of Audio Video Bridging

Figure 2 - AVB Connections

An "Audio Video Bridging" (AVB) network implements a set of protocols being developed by the IEEE 802.1 Audio/Video Bridging Task Group. AVB works by reserving a fraction of the available Ethernet bandwidth for AVB traffic. There are four primary differences between the proposed architecture and existing 802 architectures:

Precise synchronization,
Traffic shaping for media streams,
admission controls, and
Identification of non-participating devices.

These are implemented using relatively small extensions to standard layer-2 MACs and bridges. This "minimal change" philosophy allows non-AVB and AVB devices to communicate using standard 802 frames. However, as shown in Figure 2, only AVB devices are able to: a) reserve a portion of network resources through the use of admission control and traffic shaping and b) send and receive the new timing-based frames. AVB packets are sent regularly in the allocated slots. As the bandwidth is reserved, there will be no collisions.

IEEE 802.1AS - Precise synchronization

AVB devices periodically exchange timing information that allows both ends of the link to synchronize their time base reference clock very precisely. This precise synchronization has two purposes:

To allow synchronization of data streams
To provide a common time base for sampling/receiving data streams at a source device and presenting those streams at the destination device with the same relative timing.

The protocol used for maintaining timing synchronization is specified in IEEE 802.1AS, which is a very tightly-constrained subset of another IEEE standard (IEEE 1588), with extensions to support IEEE 802.11 and also generic "coordinated shared networks" (CSNs – examples include some wireless, coaxial cable, and power line technologies). IEEE 1588 is used for industrial control and test and measurement applications.

Figure 3 – Clocking hierarchy

An 802.1AS network timing domain is formed when all devices follow the requirements of the 802.1AS standard and communicate with each other using the IEEE 802.1AS protocol. Within the timing domain there is a single device called the grandmaster that provides a master timing signal. All other devices synchronize their clocks with the grandmaster as shown in Figure 3.
The device acting as grandmaster can either be auto selected or can be specifically assigned (e.g., if the network is used in a professional environment that needs "house clock" (audio), or "genlock" (video), or if the timing hierarchy needs to be specified for other reasons). AVB devices typically exchange capability information after physical link establishment. If peer devices on a link are network synchronization capable they will start to exchange clock synchronization frames. If not, then an AVB timing domain boundary is determined (as shown in Figure 2).

IEEE 802.1Qav - Traffic shaping for AV streams

In order to provide professional AV services, the AVB architecture implements traffic shaping using existing 802.1Q forwarding and priority mechanisms but also defines a particular relationship between priority tags and frame forwarding behaviour at endpoints and bridges. Traffic shaping is the process of smoothing out the traffic for a stream, distributing its packets evenly in time. If traffic shaping is not done at sources and bridges, then the packets tend to "bunch", i.e. agglomerate, into bursts of traffic that can overwhelm the buffers in subsequent bridges, switches and other infrastructure devices. "bunching" is described in greater detail in the following sections.

Tagging requirements at the stream source and the bridge

AVB streams consist of 802 frames with priority tagging and with normal restrictions on format and length. The default 802.1Q tagging for a particular market segment should be chosen to avoid potential conflict with existing uses of the 802.1Q priority tags within that market segment.

Traffic shaping at the stream source

Endpoint devices are required to transmit frames very evenly for a particular stream based on the AVB traffic class and on the specific quality of service (QoS) parameters that were used when the stream was OK'd by the network (see Admission controls below). The specific rules for traffic shaping are described in the IEEE 802.1Qav specification, and are a simple form of what is known as "leaky bucket" credit-based fair queuing where the bandwidth reserved for a stream controls the time between the packets that make up the stream.

Figure 4 – Example Qav traffic shaping

Traffic shaping at an AVB bridge

The traffic shaping mechanism used by stream sources is also employed by AVB bridges. AVB frames are forwarded with precedence over Best Effort traffic (i.e., reserved AVB stream traffic traversing an AVB bridge has forwarding precedence over non-reserved traffic) and will be subjected to traffic shaping rules (they may need to wait for sufficient credits). Just like for stream sources, the traffic shaping rules for bridges require that frames be distributed very evenly in time, but only on an aggregate class basis rather than on a per-stream basis. This means that all the AVB traffic being transmitted out of a particular port is distributed evenly in time measured using the QoS parameters of that class; this is the sum of the bandwidths of all the reservations for a particular AVB class for the particular port, made by the admission control process described below. This is to achieve the effect of smoothing out the delivery times (preventing bunching of frames ) while a stream propagates through a network. The limited bunching provides the very useful benefit of placing a relatively small upper limit on the size of the AVB output buffers needed at all egress ports on a bridge, independent of the number of hops in the path. This bounded buffer size is a key attribute that enables bounded delay and eliminates network congestion for admitted AV streams in AVB networks even when non-admitted traffic does experience congestion.

IEEE 802.1Qat - Admission controls

Even though the preceding mechanism can reliably deliver data with a deterministic low latency and low jitter, it will only do so if the network resources (e.g., throughput on a port, buffer space in a bridge) are available along the entire path from the talker to the listener(s). In the AVB protocols, the term 'talker' denotes a stream source while 'listener' denotes a stream destination. In this architecture, it is both the talker's and the listener's responsibility to guarantee the path is available and to reserve the resources. The process to do this is specified by the 802.1Qat "Stream Reservation Protocol" (SRP). This protocol registers a stream and reserves the resources required through the entire path taken by the stream: Talkers initiate by sending an SRP "talker advertise" message. This message includes a Stream ID composed of the MAC address of the stream source plus a talker-specific 16-bit unique ID and the MAC address of the stream destination. Additionally, the "talker advertise" message includes QoS requirements (e.g., AVB traffic class and data rate information), and accumulated worst case latency. Even though the address and QoS requirements are originated by the talker, the worst case latency is recalculated at every bridge allowing the listener to communicate this information to higher layers for media synchronization sake.

Figure 5 – Successful reservation (talker advertise)

Figure 5 – Successful reservation (talker advertise) All AVB intermediate bridges receiving a "talker advertise" message check for bandwidth availability on their output ports. When the bridge has got sufficient resources available on that port, then the "talker advertise" is propagated to the next station. When those resources are not available, rather than propagating the advertise message, the bridge sends a "talker failed" message. Included in this message is a failure code and bridge identification allowing a higher-layer application to provide error checking or notification. An intermediate bridge receiving a "talker failed" should just pass on the message out towards the listener. When a listener receives a "talker advertise" message, it should know whether the resources are available, and if so, the latency for the path. It can then respond with a "listener ready" message that is forwarded back towards the talker. Intermediate bridges use the "ready" message to lock down the resources needed by the stream and to make the appropriate entries in their forwarding database to allow the stream to be sent on the port that received the "ready" message. When the talker receives a "ready" message, it can start transmitting the stream.

Figure 6 – Reservation acknowledge (listener ready)

The talker can explicitly tear down a stream by de-registering the "talker advertise", and a listener can disconnect by de-registering the "listener ready". A de-registration message propagates through the network in the same manner as the original registration. There are also implicit methods used for tearing down a connection and for releasing the allocated resources. For example, the listener must periodically resend registrations and "ready" messages, and talkers must periodically resend "advertise" messages. That way any receiving device (including intermediate bridges) could automatically release assigned resources and notify higher layers if the appropriate registrations and reservations were not received due to a system halt, for example, suddenly lost power.

LAN-specific considerations

Although the intent of the AVB Task Group is to provide a LAN-technology-independent method for requesting and providing streaming services, the characteristics and architectures of different LAN technologies require specific ways of implementing those services as outlined in the next few sections.

IEEE 802.3 / Ethernet Links

Today's Ethernet devices predominantly support full-duplex operation at 100 Mbit/s or greater. Thus, since the total available bandwidth available over such an Ethernet link is both known and constant, an AVB reservation over those Ethernet links combined with the appropriate traffic shaping assures both throughput and delivery latency parameters are met for packets of reserved streams. Since the bandwidth and delivery timing cannot be assured between two devices in an older shared CSMA/CD Ethernet using hubs, these older technologies are not supported by AVB. AVB's Ethernet time synchronization standard, 802.1AS, leverages and simplifies deployed IEEE 1588-2008.

IEEE 802.11 / Wireless LAN

To date, the AVB support planned for 802.11 is limited to time synchronization. 802.1AS provides for accurate time synchronization over 802.11 links, in part by invoking MAC-specific timestamp-reporting primitives defined in IEEE Std 802.11v-2011. The time synchronization protocol defined by 802.1AS has been designed to be resilient to the transmission characteristics that are possible on wireless medium.

Coordinated Shared Network Links

Several MAC/PHY specifications and standards are currently deployed or being developed which operate over existing wires within the home (e.g. AC power lines, coax cabling,). These wires are electrically "Shared" between multiple devices (not point-to-point like Ethernet), so to provide predictable performance, transmission of information onto the wire is "Coordinated" to avoid collisions by one of the devices on the network. Such networking technologies are typically called Coordinated Shared Networks (CSN). If the CSN provides an access method with bounded latency (as most do), and if accurate link-specific time stamping or clock distribution is available for the CSN, then extensions can be defined to take advantage of them.

IEEE 802.1BA - Identification of participating devices

Since the whole AVB scheme depends on the participation of all devices between the talker and listener, any network element that does not support AVB (including so-called "unmanaged bridges") must be identified and flagged. The process to do this is described in the developing IEEE 802.1BA "Audio Video Bridging Systems" standard, which specifies the default configuration for AVB devices in a network. For Ethernet, the method specified by 802.1BA to determine if its peer is AVB capable is a combination of 802.3 link capabilities (determined during Ethernet link establishment) and the link delay measurements done by IEEE 802.1AS. An AVB capable Ethernet port uses AVB if:

the link is full duplex 100 Mbit/s or greater
the 802.1AS protocol discovers exactly one peer
the round-trip delay to the responding AVB device is no more than a worst case wire delay (computed from the IEEE 802.1AS "PDelay" exchange) Note: the worst case wire delay is less than that of a non AVB switch
an SRP reservation request or acknowledge is received on the port

Other layer 2 connections will have their own specific methods to identify cooperating peers. Even though a port may be enabled for AVB operation, there is a possibility that a complete end-to-end AVB connection cannot be made to another endpoint device that is AVB enabled. For example, in Figure 2 above, devices in AVB domain 1 cannot establish an AVB connection to devices in AVB domain 2. An AVB connection can only be assured if a successful reservation is made using SRP and SRP "talker advertise" messages will not be propagated by a non-AVB bridge.

Higher layer protocols

For applications to take advantage of the features of AVB, there needs to be some coordination with portions of the higher layer communication protocols in between. In addition, some transport protocols have been adapted to provide information for applications to use AVB. An application can implement synchronized distributed rendering using 802.1AS and higher layers. Specific audio samples and/or video frames carried by higher-layer protocols are given an associated presentation time (in terms of the shared 802.1AS clock) by the media source that is also an AVB talker. Each media renderer, that is also an AVB listener, renders the referenced audio sample or video frame at the 802.1AS presentation time.

IEEE 1722 and IEEE 1722.1

Applications using IEC 61883 and other formats can use procedures defined in IEEE Std 1722-2011 to sample the 802.1AS clock relevant for an A/V data block and then add the worst case transport delay to the sample time to get a presentation time which is inserted into the 1722 packet.
IEEE Std 1722.1-2013 is a standard which allows AVB Discovery, Enumeration, Connection management and Control (AVDECC) of devices using IEEE Std 1722-2011.

IEEE 1733

If an application uses the IETF Real-time Transport Protocol (RTP), it can use a new RTCP payload format defined in IEEE 1733^[14] that correlates the RTP timestamp with the 802.1AS presentation time. The applications at the renderer(s) then use that correlation to translate the RTP timestamp to the presentation time stamp allowing the renderer(s) to start playing at the same time and keep playing at the same rate.

HTTP

Applications using HTTP can also take advantage of AVB's time synchronization by carrying a presentation time. For example, MPEG2 transport streams that require clock synchronization between the server and client can include transport time stamps (TTS) as defined by ARIB TTS (ARIB STD-B24) which are derived from the 802.1AS clock. Similarly, an application could utilize clock synchronization through methods described in ISO 13818-1 Annex J which includes a discussion of various clock recovery schemes proposed for MPEG2 Transport Streams over jitter inducing networks, and figure J.2 illustrates a simple way to use the 802.1AS clock for this purpose.
If the media source is not a real-time source (e.g. a media file on a mass storage device), the presentation times can be generated based on the nominal media rate. If the media source is a real-time source (e.g. a microphone), the presentation time can be constructed by the talker based on its observation of the 802.1AS time in relation to the microphone's sample clock. Other higher layer services can use AVB in a similar way. Existing connection management schemes, for example, can use the AVB SRP reservation services by mapping their internal stream identifiers with the SRP stream ID. Once a connection is established, streaming can start. E.g., applications using RTP transmit RTCP packets defined by IEEE 1733 that correlate the SSRC to the SRP stream ID. Furthermore, listener applications using 1722 use the SRP stream ID to discriminate between different streams.

Standardization

Standard	Title	Status	Date
IEEE 802.1BA-2011	Audio Video Bridging Systems	Ratified and published	30 September 2011
IEEE 802.1Qav	Forwarding and Queuing Enhancements for Time-Sensitive Streams	Ratified and published	5 January 2010
IEEE 802.1Qat	Stream Reservation Protocol (SRP)	Ratified and published	30 September 2010
IEEE 802.1Q-2011	Incorporates IEEE 802.1Qav and IEEE 802.1Qat	Ratified and published	31 August 2011
IEEE 802.1AS-2011	Timing and Synchronization for Time-Sensitive Applications in Bridged Local Area Networks	Ratified and published	30 March 2011
IEEE 1722-2011	Layer 2 Transport Protocol for Time Sensitive Applications in a Bridged Local Area Network	Ratified and published	6 May 2011
IEEE 1733-2011	Layer 3 Transport Protocol for Time Sensitive Applications in Local Area Networks	Ratified and published	25 April 2011
IEEE 1722.1-2013	Device Discovery, Enumeration, Connection Management and Control Protocol for 1722-Based Devices	Ratified and published	23 August 2013

Standardization efforts are ongoing in IEEE 802.1. The following AVB improvement projects are proposed or in progress.

Standard	Function Group	Title	Status	Updated Date
IEEE 802.1ASbt	Timing and Synchronization	Enhancements and Performance Improvements	Draft 0.7	November 1, 2014
IEEE 802.1Qbv	Forwarding and Queuing	Enhancements for Scheduled Traffic	Draft 2.1	October 24, 2014
IEEE 802.1Qbu	Forwarding and Queuing	Frame preemption	Draft 1.1	October 16, 2014
IEEE 802.1Qca	Stream Reservation (SRP)	Path Control and Reservation	Draft 1.1	September 26, 2014
IEEE 802.1CB	Stream Reservation (SRP)	Frame Replication and elimination for Reliability	Draft 0.5	November 3, 2014
IEEE 802.1Qcc	Stream Reservation (SRP)	Enhancements and Performance Improvements	Draft 0.2	November 1, 2014

Networking Hardware: A Beginner’s Guide to Connected Devices

Communication Technology Bridge

The growth of the internet, bluetooth, wifi, and GPS have demonstrated the benefits of connectivity in today’s world. Have you ever stopped to think about the billions of tiny bits of hardware that make this connectivity possible? Networking hardware and infrastructure is complex and fascinating. It’s the physical receivers, chips, a

Image source: http://ccsbmt.com/blog/networking-hardware

nd transmitters that make connectivity possible in our day to day lives.

Including cell phones, computers, smart TVs, routers, modems, and GPSs, there are billions of devices connected to the internet, and the number is growing daily. A new trend in networking, the internet of things, promises to skyrocket the number of devices on the network over the coming years as stop lights, thermostats, security systems, and even your home refrigerator integrate and communicate with the other devices in your life.

While the seamless automation and efficiency of the internet of things promises to bring new levels of productivity, it also presents challenges as it increases the load on existing network hardware that currently powers the internet. This article will introduce you to the basics of networking hardware and discuss some of the challenges facing network engineers in the years to come.

Networking Hardware: A Brief Introduction

Image source: https://fcit.usf.edu/network/chap3/chap3.htm

First Off

It wasn’t so long ago that computers stood alone, unconnected to the internet. Dialup internet, the first implementation of internet connection for most home users, didn’t become widely adopted until the late-1990s. In those days, the 56 Kbps modem was the most common network device allowing your computer to communicate with other computers on the internet via the phone line, and if someone in your house picked up the telephone, you’d lose your internet connection.

Second

Since then, internet speeds have increased exponentially. According to CNN, the average American home internet has now reached speeds over 50 Mbps. That’s nearly 1000 times faster than internet in the 1990s. Although the technology and means of delivery have changed dramatically, you still need a piece of networking hardware, called a modem to receive data from the internet and decode it into meaningful information for your computer to use. This is the first basic piece of in-home networking hardware: the modem that connects you to the internet.

Thirdly

In most homes, you no longer have to plug in a cord to connect to the internet. Wifi technology comprises the second stage of in-home networking hardware. A wireless router communicates with your modem and broadcasts the modem’s signal to your home. This allowing you to move freely around the house with your wifi-enabled devices. Each of these devices – like your phone, tablet, or laptop – has a piece of networking hardware inside of it. That little piece of networking hardware allows it to send and receive signals from the wireless router.

Lastly

A new trend is adding connectivity to other devices in your home, like your thermostat or alarm system. These connected devices that aren’t computers make up what’s known as the internet of things, and it’s growing. However, in 2017, only about 10% of consumers have such connected devices in their homes, so the internet of things still remains outside of the mainstream. Over the coming years that will change. By 2020, according to Gartner research, there will be 25 billion devices connected to the internet of things, not only in your home but also on the street, in stores, and everywhere in daily life.

Low Power Solutions: Why Using and Connecting to a Bluetooth Device Makes Sense

Image source: https://www.pcworld.idg.com.au/article/624948/bluetooth-devices-could-soon-mesh-networking-capabilities/

Think About This

As the internet of things grows, it becomes increasingly difficult for companies and consumers to manage and power their devices. In fact, according to Network Computing, powering devices is one of the main challenges for IoT and networking hardware infrastructure. The sheer number of devices means that power management and energy saving measures are going to be paramount to the successful implementation of connected devices. Especially for companies with large networks of devices.

Don’t Forget That

Sometimes, connecting to bluetooth device infrastructures may make sense. Bluetooth technology has been around for over twenty years, and it’s well-understood. It uses lower energy wavelengths than wifi to deliver information. Most of us are familiar with bluetooth. We may occasionally use bluetooth to pair our phones with our car speakers or a wireless headset. However, Bluetooth has potential for broader applications, and the low energy requirements of Bluetooth make it an attractive alternative for connecting networking hardware.

Overall, connecting devices to the network has huge potential to facilitate and automate everyday life. In the near future, your fridge could tell you when you’re out of milk. Your car will likely connect to the internet while you’re driving so it can communicate with other cars on the road. This will offer entertainment options for passengers. You’ll increasingly see in-store devices at clothing retailers and grocery stores. These are items that help you find items and give the store feedback on new things you’d like to purchase. All these applications and more are coming in the near future, thanks to advances in networking hardware.

      XO___XO +DW DW SAW % Electronics and Communication ( e- Bridge )

The world's reliance on electronics is so great that commentators claim people live in an"electronic age." People are surrounded by electronics—televisions, radios, computers, mobiles, Laptop and DVD players, along with products with major electronic control components, such as microwave ovens, refrigerators, and other kitchen appliances, automatic vehicles, Robotics, as well as hearing aids and medical instruments and numerous applications in industry. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements; such a circuit is described as an electronic circuit . Consumer electronics:include products like–Audio Systems, Video Systems, TV (Television),Computer, Laptop, Digital Camera, DVD Players, Home and Kitchen Appliances, GPS, Mobiles Phones etc.
Communication:Electronic communication systems connect people around the world. Using telephones, Internet and computers, people in different countries communicate almost instantly. Radios transmit sounds and televisions transmit sounds and pictures great distances. Cellular telephones enable a person to call another person. Within seconds, fax machines send and receive copies of documents over telephone lines/Satellite.
Information processing: scientists, artists, students, government and business workers, and hobbyists at home all rely on computers, Internet to handle huge amounts of information quickly and accurately. Computers solve difficult mathematical problems, maintain vast amounts of data, create complex simulations, and perform a multitude of other tasks that help people in their everyday lives.

Medicine and research: include product like X-ray machines ECG (Electrocardiogram) use radiation to take images of bones and internal organs. Radiation therapy, or radiotherapy, uses X-rays and other forms of radiation to fight cancer. Many hearing-impaired people depend on hearing aids to electrically amplify sound waves.

Computers : and other electronic instruments provide scientists and other researchers with powerful tools to better understand their area of study. Computers, for example, help scientists design new drug molecules, track weather systems, and test theories about how galaxies and stars develop . Electron microscopes use electrons rather than visible light to magnify specimens 1 million times or more.

Automation: Electronic components enable many common home appliances, such as refrigerators, washing machines, and toasters, to function smoothly and efficiently. People can electronically program coffeemakers, lawn sprinklers, and many other products to turn on and off automatically. Microwave ovens heat food quickly by penetrating it with short radio waves produced by a vacuum tube.

Instrumentation: Measuring Instruments like CRO, Multimeter, ph-meter, strain gauge, VTVM, Frequency Counter are used in different Laboratory/organizations. Many automobiles have electronic controls in their engines and fuel systems. Electronic devices also control air bags, which inflate to protect a driver and passengers in a collision .


   IoT combine and conjuntion with Electronics circuits

The Internet of Things promises convenience, marked improvements in efficiencies, and huge economic benefits, but for such visions to be realized the number of physical devices being integrated with the digital world needs to continue increasing. But limiting the expansion, and ultimate ubiquity, of this technology has been the cost, power and size of the enabling electronics – all things that have been addressed by a new fabrication method.

Researchers at Purdue University and the University of Virginia are just the latest to take on the challenge of getting physical objects connected to the IoT cheaper and easier. To this end, they've developed a new ultra-thin circuit fabrication method that promises to bring the IoT to pretty much any object you can slap a label onto.

The process behind these peelable electronic circuits not only eliminates a number of manufacturing steps, thereby reducing cost, but it also means almost any object can act as a sensor or be controlled via the application of high-tech decals.

Of course, thin-film materials are nothing new, but this wafer-recyclable, transfer-printing process, using combinations of active nano-materials is a step into the future, both technologically and environmentally.

Conventionally, most electronic circuits are printed on rigid silicon wafers. These stiff substrates need to be resilient enough to withstand the heat and chemical etching of the process, and as such, the wafer is replaced each time a new circuit is printed. This new technique, called "transfer printing," allows a single wafer to be used over and over to build a near infinite number of flexible film-based circuits, which can be easily peeled off at room temperature by submerging the wafer and completed circuit in water.

"It's like the red paint on San Francisco's Golden Gate Bridge – paint peels because the environment is very wet," says Chi Hwan Lee, Purdue assistant professor of biomedical engineering and mechanical engineering. "So in our case, submerging the wafer and completed circuit in water significantly reduces the mechanical peeling stress and is environmentally friendly."

Researchers have designed peelable electronic films that can be cut and pasted onto any object to...

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Selasa, 23 Oktober 2018

Computation Structures

Wheatstone bridge and Its Working

Wheatstone Bridge and Its Working

Wheatstone Bridge Circuit Arrangement

Example of Wheatstone Bridge

Application of Wheatstone Bridge

The Wheatstone Bridge

Wheatstone Bridge Circuit

Wheatstone Bridge Example No1

Wheatstone Bridge Light Detector

Wheatstone Bridge Light Detector

The Wien Bridge Oscillator

RC Phase Shift Network

Oscillator Output Gain and Phase Shift

Wien Bridge Oscillator Frequency

The RC Network

Series Circuit

Parallel Circuit

Wien Bridge Oscillator

Wien Bridge Oscillator Example No1

Wien Bridge Oscillator Lowest Frequency

Wien Bridge Oscillator Highest Frequency

Wien Bridge Oscillator Example No2

Wien Bridge Oscillator Circuit Example No2

Wien Bridge Oscillator Summary

Maxwell’s Bridge

Types of Maxwell’s Bridge

Maxwell’s Inductance Bridge

Advantages of the Maxwell’s Bridges

Disadvantages of the Maxwell’s Bridge

H-bridge paves new ways for LED lighting

Derivation

Input impedance

Transfer function

Bridged T implementation

Types of section

Attenuator

Low pass

High pass

Band pass

Band stop

Practical sections

Basic loss

6 dB/octave roll-off

Mismatched lines

Bumps and dips

Transformer roll-off

Temperature compensation

Kelvin Bridge

What is the need of Kelvin Bridge?

Modification of Wheatstone Bridge

Kelvin Double Bridge Circuit

Limitations of Kelvins Bridge

Campbell’s Bridge

Anderson’s Bridge

Constructions of Anderson’s Bridge

Phasor Diagram of Anderson’s Bridge

Theory of Anderson Bridge

Advantages of Anderson Bridge

Disadvantages of Anderson Bridge

Carey-Foster Slide-Wire Bridge

The Carey Foster Bridge is used for measuring the low resistance or for the comparison of two nearly equal resistances. The working principle of the Carey foster bridge is similar to the Wheatstone Bridge.

Calibration of Slide Wire

AC Bridge

The bridge uses for measuring the value of unknown resistance, inductance and capacitance, is known as the AC Bridge. The AC bridges are very convenient and give the accurate result of the measurement.

General Equation for an AC Bridge

Advantages of Hybrid Stepper Motor

Disadvantages of Hybrid Stepper Motor

Step Angle in Stepper Motor

Advantages of Stepper Motor

Disadvantages of Stepper Motor

Advantages of Stepper Motor:

Applications:

Operation of Stepper Motor:

Stepper Motor Control by Varying Clock Pulses

ypes

Features

Applications

Basic Variable Speed Motor/Switch