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Using a Polar Heart Rate Monitoring Chest Band

A project log for Dream Catcher

Life-changing circumstances led me to begin having Nightmares in which I would wake up finding my pillow soaking wet, and vivid memories it.

grayson-schlichtingGrayson Schlichting 07/11/2016 at 06:370 Comments

I started out with the Polar Chest Band which transmits heart rate wirelessly (via Bluetooth or a proprietary RF method). I used the Non-Bluetooth model to simplify the project since the receiver board is just that; it requires no setup or programming. It just sends out a 20ms. pulse (ha ha) on each heartbeat it receives from the band.

Starting point was this:

Heart Rate Educational Starter Pack with Polar Wireless Sensors

from Adafruit: https://www.adafruit.com/products/1077

The Polar bands use electrical pick-up pads to detect heart beats, and you have to wear it just under you pectoral region. It's a bit uncomfortable, but it was where I started.

Heart Rate Educational Starter Pack with Polar Wireless Sensors

This picture is from Adafruit.com. With the parts included, you can wire it up and see your pulse on that (jumbo) red LED. Pictured are a battery holder for 3V to power the receiver board (the Polar has an internal CR2032 for powering the EKG sensor and the transmitter). You wear the sensor band as described across your chest, and what is pictured left and above the band is the adjustable elastic band that holds it around your torso.

The resistor is for current-limiting the LED, and you can see the Receiver Board which has only 3 pins: power, ground, and out. Snap off all but 3 of the header peices, solder them to the RX PCB, and plug it all into the provided Protoboard and you can watch the LED flash as your heart beats.

For my first prototype, I sent the Receiver's Out pin to a GPIO pin on an Adafruit Trinket (small Arduino compatible board). That's where the sensor is monitored, filtered, and analyzed. When it detects a rise in heat rate of x% over time (t) then "something" is happening. If you are having a dream so intense that it causes you to sweat, then your heart rate WILL increase. Your "x%" and "t" will vary. For the final build, I am considering perhaps 2 potentiometers for setting this.

When a threshold is detected, then the Trinket is used to drive the nRF24L01 transceiver which wirelessly connects to the "alerting device" - in my case, I have it drive a small vibrating motor stuck to my headboard which resonates loud enough to wake me up.

I used this: https://www.adafruit.com/products/1201

I am happy with the "receiving-side" of the project, but really needed a way to measure heart rate more "comfortably."

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