Simple ECG Circuit

ECGs are an amazing diagnostic tool that help diagnosis various heart conditions. This instructable will walk you through the building process of a simple ECG using basic circuit materials. This circuit will include a notch filter, low-pass filter, and an instrumentation amplifier.

To create the instrumentation amplifier (INA) with a gain of 1000, obtain a breadboard, several wires, three uA741 op-amps, two 13 kOhms resistors, one 1 kOhms resistor, and two 5.1 kOhms resistors. Connect these components using the schematic shown above.

Connect a battery supply to the breadboard to power the op-amp and send a 10mV sin wave through the circuit. The input and output can be displayed on an oscilloscope and should match the image above.

To create the notch filter with a center frequency of 60 Hz, obtain a breadboard, several wires, one uA741 op-amp, one 430 kOhms resistor, two 1.6 kOhms resistors, two 0.1 uF capacitors, and one .22 uF capacitor. Connect these components using the schematic shown above.

Connect a battery supply to the breadboard to power the op-amp and send a 10mV sin wave through the circuit using a function generator. A magnitude response plot can be created by varying the frequency of the sin wave and recording the amplitude. If the magnitude plot has a sharp drop in magnitude around 60 Hz, like the image above, then the circuit is working appropriately.

To create the low pass filter with a cutoff frequency of 150 Hz, obtain a breadboard, several wires, one uA741 op-amp, one 18 kOhms resistor, one 18 kOhms resistor, one 0.033 uF capacitor, and one .068 uF capacitor. Connect these components using the schematic shown above.

Connect a battery supply to the breadboard to power the op-amp and send a 10mV sin wave through the circuit. Display the output signal on an oscilloscope. This circuit can be verified by varying the frequency of the sin wave and noticing a drop in amplitude at 150 Hz and above.

Create the full ECG circuit by connecting the three components together as shown in the schematic. You can check to see if your circuit is still working by passing a 10 mV sin wave through your circuit and seeing if you get an expected output on your oscilloscope.

Once your circuit is connected and working, obtain 3 electrodes and place one on your right ankle, left ankle, and left wrist. The right ankle should be connected to one input of the INA circuit and the left wrist should be connected to the other input. The left ankle is ground. At this point, you should see an ECG signal on your oscilloscope that looks like the signal in the image above.

Obtain an Arduino and connect it to the output wire of your full ECG circuit. Use the Arduino code in the images above to produce a plotted ECG signal and display BPM readings.