Electrocardiogram

Project Overview

According to the World Health Organization, over 17.9 million deaths are caused due to heart and cardiovascular related diseases. It’s an unfortunate amount of deaths, but that number could be a lot higher today if it weren’t for the help of technologies such as computers, biomedical sensors, and devices like electrocardiograms.

Electrocardiograms (ECG) are one of many revolutionary technologies that have helped diagnose and detect various heart related issues such as heart attacks and irregular heartbeats (arrhythmias). Its non-invasive way of gathering data makes it a low health risk option that can provide invaluable data. Without ECGs today, it would be a lot harder to treat and anticipate heart diseases as well as monitor and maintain patients.

This part of the tutorial provides a comprehensive guide to understanding and working with ECG from the basic theory to teaching you the knowledge to build practical projects interfacing microcontrollers with ECG sensors. Theory explanations, hardware, and software procedures/experiments will give you a foundational level of understanding while you will apply and demonstrate your knowledge through a project based lab and tasks.

By the end of this section, the projects you make will show your proficiency in many aspects of ECG such as hardware (wiring and circuitry) and software (signal analysis and processing).

In total you will be building 2 ECG related projects, here is a brief description of what to expect:

• Use the AD8232 module and STEPico to build a BPM calculator that prints an average calculated BPM.

• A heartbeat monitor that lives graphs your heart activity as well as calculates BPM and displays it on the LCD display.

In order to complete the project, you will need the following materials and tools:

• 1 Breadboard

• 1 AD8232 ECG sensor

• 1 STEPico microcontroller

• 3 electrodes patches (9 recommended)

• 1 Electrodes to barrel jack cable

• 1 ST7789 1.54” 240x240 pixel LCD display

• 1 USB type-C cable

• Multiple Male to male jumper wires

• A computer with Thonny and MicroPython installed

• (Optional) Zoolark portable oscilloscope

• (Optional) MEGO power supply

Circuiting Instruction

The ECG sensor you will be using has many built in features that handles all the backend technical work for you through a series of analog amplifier and filter circuits. The sensor is called the AD8232 because it refers to the AD8232 IC that acts as the main brain for the module. The AD8232 has 6 pins but most of the time we only use 3 (GND, 3.3V, OUTPUT).

GND	negative power pin	Any GND pin on STEPico
3.3V	Input voltage positive power pin (3.3V)	3V3(OUT)
OUTPUT	Carries the amplified analog signal of the ECG reading	Any GPIO pin with ADC capability

You will also need to connect the ST7789 display.

Once you finished wiring, the circuit should be similar to the following image

In this project, we will learn how to build a 3-lead ECG. 3-lead ECG is a basic electrocardiogram setup used for monitoring heart rate and rhythm, commonly found in emergency care, ICUs, and anesthesia monitoring. It utilizes three electrodes placed on the right arm (RA, red), left arm (LA, yellow), and left leg (LL, green), forming Einthoven’s triangle.

This signal is essentially a scaled up version of the signal read from the heart. Without using the STEPico to process the signal, we could take a look at the output signal using Zoolark, the oscilloscope. Go ahead and try connecting the AD8232 to your Zoolark and check the signal.