Instrumentation amplifier are special amplifiers that are used for signal acquisition of low amplitude with noise. Among other things they have high common signal rejection ratio and high input impedance and low output impedance. They are found in discrete integrated circuit but one can also build instrumentation amplifier from op-amps. The three op-amp based instrumentation amplifier is popular. Here instrumentation amplifier is build on breadboard using the LM324 op-amp. The instrumentation amplifier is then tested with Proteus Software.
We had explained earlier what is instrumentation amplifier & types of instrumentation circuits and showed LM324 Op-Amp Instrumentation amplifier design example using ac coupling, basing and with single supply. Here the LM324 instrumentation amplifier is build using dual supply obtained from single supply of +9V and the amplifier is dc coupled.
Following video shows the LM324 instrumentation amplifier build on breadboard and tested with Proteus Software.
The schematic diagram of the LM324 instrumentation amplifier is shown below.
Here we have used a single supply voltage of +9V and split it using resistors R8 and R9 to get dual supplies +4.5V and -4.5V for the LM324 op-amp. The input signal, a sine wave for testing purpose is applied to the Vin1 and Vin2(ground wire of signal is applied here). The R5 is used to adjust the gain of the instrumentation amplifier and also make to differential input off equal. The third op-amp has equal resistors of 1KOhm so that the gain is unity. Hence the overall gain of this instrumentation is provided by the ratio of the resistors Rf1(=Rf2) and R5. The gain of instrumentation amplifier is given by the following equation,
\[A = \frac{V_{out}}{V_{in2}-V_{in1}} = \frac{R_{2}}{R_{1}}(1+\frac{2 R_{f}}{R_{5}})\]
where, \(R_{f1} = R_{f2} = R_{f}\) and \(R_{2} = R_{3}\), \(R_{1} = R_{4}\)
Therefore,
\[A = 1+\frac{2 R_{f}}{R_{5}}\]
The following picture shows the LM324 instrumentation amplifier on a breadboard.
To test the LM324 instrumentation amplifier on the breadboard in real time with actual signal we will use Proteus Software. The Proteus software has speaker and microphone components which can be used to send out signal from the PC speaker and acquire signal using the microphone/line in port of the PC. The following shows how the speaker and the microphone component in Proteus electronics design Software are used in this tutorial.
In the above picture, a signal generator or function generator is connected to the speaker. The function generator can be used to output various types of signals such as sine wave, triangle wave, square wave etc. We can control the signal amplitude and frequency of the generated signal. The generated signal is then sent to the PC speaker. The signal generator control panel in proteus software is shown below.
The signal which is sent out from the PC speaker is then fed into the instrumentation amplifier on the breadboard using male to male audio jack. The output from the amplifier is then sent into the microphone/line in input of the PC. This signal is collected by the microphone component in proteus software as shown above. The output of the microphone component is connected to the oscilloscope. The output of the instrumentation amplifier can then be viewed on the oscilloscope in real time.
The following shows the input and output waveform on the oscilloscope obtained in real time.
How to connect the signal output from the PC speaker to the amplifier input on the breadboard using male to male audio jack and how to connect the amplifier output to the mic/line in port of PC was shown in the tutorial LM741 non-inverting amplifier with dual supply from single supply.
In this example tutorial we have used Proteus Software for testing the circuit. If you don't have Proteus Software, the instrumentation amplifier circuit above can also be tested using Matlab/Simulink based oscilloscope and spectrum analyzer as was done in the following tutorials.
- LM324 op-amp Integrator testing with matlab simulink oscilloscope
- Square wave to Triangle Wave with LM324 Op-amp
- Function generator using LM324 op-amp
Or, one can also use Labview Software based oscilloscope and function generator as was illustrated in the following tutorials.
- How to Build BJT amplifier and test with Soundcard based PC Oscilloscope
- Testing of self biased BJT amplifier on breadboard with PC oscilloscope
