AD8232 Ecg module - MohanadSinan/IoT-Based-Healthcare-System GitHub Wiki
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| AD8232 Ecg module | AD8232 Ecg module Pinout |
Features and Specifications
- Operating Voltage: 3.3V
- Analog Output
- Leads-Off Detection
- Shutdown Pin
- LED Indicator
- 3.5mm Jack for Biomedical Pad Connection or Use 3 pin header
Note: This product is NOT a medical device and is not intended to be used as such or as an accessory to such nor diagnose or treat any conditions.
Pin Configuration
| Pin No. | Pin Name | Description |
|---|---|---|
| 1 | GND | Common Cathode terminal (Ground) |
| 2 | 3.3v | 3.3v Power Supply |
| 3 | OUTPUT | Analog Output Signal |
| 4 | LO- | Leads-off Detect - |
| 5 | LO+ | Leads-off Detect + |
| 6 | SDN | Shutdown |
Note: The AD8232 Ecg module Datasheet can be found at the bottom of the page
Understanding the ECG
The ECG is separated into two basic Intervals, the PR Interval and the QT Interval, described below.
PR Interval
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!
QT Interval
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.
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| Heartbeat with corresponding ECG |
How to Connect AD8232 Ecg module's Headers to the Board?
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.
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| Headers installed |
Follow the diagram below, to make necessary connections. The SDN pin is not used in this demo. Connecting this pin to ground or “LOW” on a digital pin will power down the chip. This is useful for low power applications.
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.
| Cable Color | Signal |
|---|---|
| Black | RA (Right Arm) |
| Blue | LA (Left Arm) |
| Red | RL (Right Leg) |
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| Sensors connected to Heart Monitor |
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| Typical Sensor Placements |
How to Connect to Arduino?
| Board Label | Arduino Connection |
|---|---|
| GND | GND |
| 3.3v | 3.3v |
| OUTPUT | A0 |
| LO- | 11 |
| LO+ | 10 |
| SDN | Not used |
Tips and Tricks
ECG’s are notoriously noisy. This is because you are measuring muscle activation. The further sensor pads are from the heart, the more muscle noise you will see. These are commonly referred to as “Motion Artifacts”. So here are some simple tips to improve the signal quality.
- Keep sensor pads as close to the heart as you can.
- Make sure the RA and LA sensor pads are on correct sides of the heart.
- Try not to move too much while taking a measurement.
- Try to use fresh pads for each measurement. The pads loose the ability to pass signals with multiple applications.
- Prep and clean the area you plan to stick pads. This will help make a good connection (hair is not a good conductor).
- You may have to adjust sensor placement for different individuals.
Applications
- Fitness and exercise heart rate monitoring
- Portable ECG
- Remote health care
- Gaming peripherals
- Biological signal acquisition