The AD8232 is a neat little chip used to measure the electrical activity of the heart. This electrical activity can be charted as an ECG or Electrocardiogram. Electrocardiography is used to help diagnose various heart conditions. Now for the disclaimer:
NOTE: This device is not intended to diagnose or treat any conditions.
In general terms, lets look at what an ECG is representing and how we’re able to sense it. The ECG is separated into two basic Intervals, the PR Interval and the QT Interval, described below.
The PR interval is the initial wave generated by an electrical impulse traveling from the right atrium to the left. The right atrium is the first chamber to see an electrical impulse. This electrical impulse causes the chambers to “depolarize”. This forces it to contract and drain deoxygenated blood from both the Superior and Inferior vena cava into the right ventricle. As the electrical impulse travels across the top of the heart it then triggers the left atrium to contract. The left atrium is responsible for receiving newly oxygenated blood from the lungs into the left ventricle via the left and right pulmonary veins. The pulmonary veins are red in the diagram because they are carrying oxygenated blood. They are still called veins because veins carry blood towards the heart. Science!
The QT Interval is where things get really interesting. The QRS is a complex process that generates the signature “beep” in cardiac monitors. During QRS both ventricles begin to pump. The right ventricle begins to pump deoxygenated blood into the lungs through the left and right pulmonary arteries. The pulmonary arteries are blue in the diagram because they are carrying deoxygenated blood. They are still called arteries because arteries carry blood away the heart. Science, Again! The left ventricle is also begining to pump freshly oxygenated blood through the aorta and into the rest of the body. After the initial contraction comes the ST segment. The ST segment is fairly quiet electrically as it is the time where the ventricals waiting to be “re-polarized”. Finally the T wave becomes present to actively “re-ploarize”, or relax the ventricles. This relaxation phase resets the ventricles to be filled again by the atriums.
In this guide, we’ll connect the AD8232 Breakout to an Arduino microcontroller. We will build a simple cardiac monitor that will allow you to measure the electrical activity of the heart in real time!
The AD8232 Heart Rate Monitor breaks out nine connections from the IC. We traditionally call these connections “pins” because they come from the pins on the IC, but they are actually holes that you can solder wires or header pins to.
We’ll connect five of the nine pins on the board to your Arduino. The five pins you need are labeled GND, 3.3v, OUTPUT, LO-, and LO+.
|Board Label||Pin Function||Arduino Connection|
|3.3v||3.3v Power Supply||3.3v|
|LO-||Leads-off Detect -||11|
|LO+||Leads-off Detect +||10|
You can use any method you’d like to make your connections to the board. For this example, we’ll solder on a five-pin length of male-male header strip and use a breadboard and jumpers to make our connections.
Now that the electronics are complete, let’s look at sensor pad placement. It is recommended to snap the sensor pads on the leads before application to the body. The closer to the heart the pads are, the better the measurement. The cables are color coded to help identify proper placement.
|Black||RA (Right Arm)|
|Blue||LA (Left Arm)|
|Red||RL (Right Leg)|
How to connect electrodes to human body