Make an ECG!

What is an ECG?

An electrocardiogram(ECG) is a device that is used to record electrical signals within the heart. It records the electrical activity through electrodes that are attached to various parts of your body. ECGs will be able to see your heart rhythm, diagnose heart attacks, and understand if there are any abnormalities[1].

Within an ECG reading, there is a P wave, Q wave, R wave, S wave, T wave and a QRS complex. These waves are present in every person's ECG and will help a physician identify any abnormalities. To create a circuit that will be able to measure an ECG, we used a differential amplifier, a low pass filter, and a notch filter.

The differential amplifier amplified our signal, the low pass filter got rid of noise from higher frequencies, and the notch filter removed any noise at 60 Hz that could be coming from nearby devices.

The supplies you will need are listed below:
1 Breadboard

5 operational amplifiers(UA741)

Resistors:

2 x 48k

3x 1.6k

2x 1k

2x 30k

1x 424k

2x 22k

Capacitors:

3x 0.1e-6F

1x 6.67e-8F

1x 3.33e-8F

Jumper wires

a DC Voltage Power Supply

Function Generator

Oscilloscope

3 electrodes

Alligator Clips

The purpose of the differential amplifier is to amplify the signal so that it will be displayed on the oscilloscope. The schematic of the setup has been attached to this step in order to help in designing the breadboard schematic. Using our setup, the signal should be amplified by approximately 1800, however, based on the chosen resistor values, this may change.

The purpose of the Notch filter is to eliminate any noise around 60 Hz that could be caused by nearby devices. We have included a picture of the schematic, and the specific part on our breadboard that will eliminate this noise. To test this part of our circuit, we used a sine wave in order to compare the output to the input wave.

The low pass filter is designed to reduce noise that could occur and remove all frequencies that are higher than the ECG signal. We chose a cutoff frequency of approximately 150 Hz. We have attached a schematic that will help in connecting the low pass filter into the notch filter.

In order to get an accurate reading, use the electrode designated as Voltage Source 1 to be on your right arm, Voltage source 2 on your left ankle, and the ground on your right ankle. Once connected to the circuit, attach the output of the low-pass to the oscilloscope and observe the ECG waveform.

References:

[1]Cardiac Cycle | Anatomy and Physiology II. (n.d.). Retrieved April 27, 2022, from https://courses.lumenlearning.com/ap2/chapter/cardiac-cycle/