Op-Amp ECG Project

This page will tell you how to build an ECG using a set of operational amplifiers. Operational amplifiers are cool because you can configure them a variety of ways to serve different purposes. In this case, we will be using op-amps to build a differential amplifier for the ECG leads as well as a notch and a low pass filter to remove noise.

- 5 LM741 Components

- 100 k-ohm resistor, 10 k-ohm resistor, 47 k-ohm resistor, 1 k-ohm resistor, 1800 ohm resistor, 470 k-ohm resistor, 1500 k-ohm resistor, 22 k-ohm resistor, 2.2 k-ohm resistor

- 33 nF capacitor, 66 nF capacitor, 0.1 uF capacitors, 0.2 uF capacitors

- electrodes + electrode wires

- oscilloscope, DC power supply, AC signal supply

Construct the differential amplifier above. As shown in the image, the differential amplifier takes the voltage difference between the two electrode leads connecting to the wrist, while the ankle electrode is connected to the same ground as the circuit. This circuit is designed to have a gain of 1130. This is because the measured voltage trace from a heartbeat is very small, and a gain of 1130 amplifies the signal into something more readable.

Construct the circuit above. The circuit's components give a center frequency of 60 Hz. This means that the circuit attenuates signals at/around 60 Hz. This is because power line interference from the ECG system is around 60 Hz and must be removed from the input.

Construct the active low pass filter system in the figure above. This low pass filter has a cutoff frequency of 150 Hz. This means that the system will now only pass signals that have a frequency below 150 Hz. This cutoff frequency is the same one recommended by the American Heart Association to filter in relevant signals and remove noise.

Construct the individual pieces of your system together. The order of the low-pass filter and notch filter don't matter, but the differential amplifier must be placed first in the system. Connect the output to your oscilloscope and adjust your oscilloscope settings to see your heartbeat!