AD8232 Heart Rate Monitor Module with Electrodes

An integrated ECG/EKG device for charting the activity of the heart.

DESCRIPTION

The AD8232 Heart Rate Monitor Module with Electrodes is an integrated ECG/EKG device for charting the activity of the heart.

PACKAGE INCLUDES:

• AD8232 Heart Rate Monitor Module
• Cable assembly – Audio jack to 3 electrode snap connectors
• Qty 3 – Adhesive electrodes

KEY FEATURES OF AD8232 HEART RATE MONITOR MODULE WITH ELECTRODES:

• Built-in signal filtering and amplification
• Comes complete with electrodes
• 3.3 operation

This module is based on the Analog Devices AD8232 which is a dedicated ECG front end designed for fitness monitors, portable ECG devices, gaming peripherals and similar applications.

ECG is short for Electrocardiogram and is sometimes written as EKG. ECG relates to the process of measuring and recording the electrical activity of the heart.

An ECG gives three main kinds of information. First by measuring the time intervals, it is possible to determine how long the electrical wave takes to pass through the heart. This shows if the electrical activity is normal, slow, fast or irregular. Second, by measuring the amount of electrical activity passing through the heart, it may be possible to find out if parts of the heart are too large or overworked. Third, it provides the heart rate.

The measurement is done using 3 electrodes placed on the skin in the following locations.
1. Right arm on front of forearm or on right side of chest
2. Left arm on front of forearm or on the left side of chest
3. Right leg on middle thigh or lower right abdomen

Electrode Placement 1                                    Electrode Placement 2

 

The electrodes detect the electrical changes that occur as the heart goes through the process of heartbeat.

The electrodes pass these tiny electrical signals which are in the range of a couple hundred microvolt to an ECG monitor that processes the signals. Processing involves amplification and filtering

REPRESENTATION OF NORMAL ECG

 

and then the data is provided in a format that can be used to update a display of some type. The sensor environment is very noisy, so the trick is filtering out the important info from the electrical noise.

With the AD8232 module, the electrodes are connected via an audio jack. The buffered and filtered output is made available via an analog output that can be read by an analog input on a microcontroller.

The waveform here comes from Wikipedia and I would recommend checking out that link for more information on how to understand the waveform that is created by this device.

Module Connections

The module should be powered from 3.3V.

1 x 6 Male Header

• GND =       Ground
• 3.3V =        Connect to 3.3V
• OUTPUT = Sensor analog output – connect to analog input on MCU
• LO- =          Lead is Off – Left Arm
• LO+ =         Lead is Off – Right Arm
• SND =         Shutdown.  Pull LOW to put into low power mode

1 x 3 Male Header / Phono Jack

• RA = Right Arm Electrode
• LA = Left Arm Electrode
• RL = Right Leg Electrode

These male header and phono jack duplicate the same connections.

Practical Use Considerations

The electrode pads are large sticky pads that can be used several times.  It is easiest to snap the pads to the sensor cable before applying the pad.  When the pads are removed, the liner should be reapplied to keep the adhesive side as clean as possible.

To minimize noise in the signal, the subject should remain seated and as still as possible in order to get a reasonably stable reading.

Applying light pressure to the electrodes may help with signal acquisition.

The LED on the module will blink when electrical activity is detected.  With a fairly stable reading, the LED will blink at the heart rate and can be used as a general indication of whether the device is picking up the electrical signals.

This module is intended to provide an easy way to experiment with ECG technology.  This device should not be used as a substitute for seeing your doctor with a certified ECG machine if you think you may have heart related health issues.

OUR EVALUATION RESULTS:

The module implements the example application in the datasheet as shown here.  The layout and quality seem reasonable, but it may not be optimized.

While the device is not quite hospital grade, it does a respectable job, usually after fiddling around with it a bit to get the sensors to read well.  I find that placing the electrodes on the chest area rather than the arms seems to give the best readings, probably due to the stronger signal available in that area.

To get it up and running, simply hook the sensor up to 3.3V and ground and connect the Output pin to A0. We are also connecting the LO+ and LO- signals up to pins 8 & 9 so that we aren’t dumping useless data to Serial Plotter window when the electrode are not connected.  We are not using the SDN shutdown pin.

Download and run the following simple program, attach the electrodes and then open the Serial Plotter window.  The Serial Plotter window auto scales and so it will take a short time for the window to settle down and then you should see a waveform that looks similar to what is shown below.

AD8232 Heart Monitor Test Program

/*
   AD8232 Heart Monitor Test Program
   Reads ECG data from AD8232 module and displays it as a waveform

   Connect  to 3.3 and ground.
   Connect Output to A0 (or any analog input
   Connect LO+ to pin 8 (or any digital pin)
   Connect LO- to pin 9 (or any digital pin)
*/
const int SENSOR_PIN = A0;
const int LO_POS_PIN = 8;
const int LO_NEG_PIN = 9;
//===============================================================================
//  Initialization
//===============================================================================
void setup(void) {
  Serial.begin(9600);
}
//===============================================================================
//  Main
//===============================================================================
void loop(void) {
  if ((digitalRead(LO_POS_PIN) != 1) && (digitalRead(LO_NEG_PIN) != 1))
  {
    Serial.println(analogRead(SENSOR_PIN));  // send the value of analog input A0
    delay(1);   // Delay slightly so serial can keep up
  }
}

Notes: 

1. None

TECHNICAL SPECIFICATIONS