In the BM605 lab this time we made a working three lead ECG on a breadboard. We used just two amplifier chips. One of them, AD620 which is an instrumentation amplifier with following pin configuration:
And the other our very own μA741
We had tried earlier to implement this circuit with instrumentation amplifier designed out of discrete ua741 Opamps but had failed to obtain ECG signals due to enormous powerline noise pickup by body. In the following schematic we use an integrated instrumentation amplifier chip AD620 to amplify the differential signal from across the heart (Terminals 1 and 2). But still we have powerline noise pickup as common mode signal on both terminals 1 and 2. We sense the common mode voltage and feed it back to the body after multiplying with a factor of -1. This almost entirely removes the powerline noise and all features of ECG, PQRST are clearly obtained.
Our M.Tech. student Nilesh made a simulation design of the circuit implemented in this experiment.
And here is the system in action. A surprisingly clear ECG was obtained on the scope! The whole experiment was successfully completed by all groups in just two hours.
Thanks to Piyush for saving the CSV file of the data and sharing it with all.