Sunday, October 14, 2012

Heart Rate Monitor Project

As the summer drew to a close I decided that monitoring my hear rate as part of my indoor training regime would make for an interesting project and might make cycling indoors a bit more interesting. To do this I decided to interface the heart rate monitor with my Android tablet.


After doing some research I decided that there were three approaches I could take.

  1. Get a bluetooth heart rate band and interface with the tablet via bluetooth.
  2. Get an ANT capable heart rate band and interface with the tablet using ANT and the android open accessory protocol.
  3. Get a heart rate band from Polar and interface with the tablet using a Polar wireless interface board and the android open accessory protocol.

I decided to go with the ANT approach. This was partly because of cost but also due to the fact that there are other sensors including ones that measure cadence and speed that make use of ANT.

What is ANT?

ANT is a 2.4GHz wireless networking protocol and embedded system solution designed for low power wireless sensor networks. It has a focus on sensors for measuring various aspects of exercise and while it isn’t restricted to this it does seem to be a popular us case.

For the most part ANT sensors are used in combination with GPSes which provide readout and recording of the sensors. There are also a few smart phones that are ANT capable.

Heart Rate Belt

An ANT heart rate monitor consists of the sensors for picking up your heart beat and a small lower power transmitter attached to a belt or strap that is worn across the chest. The sensor picks up the heart beats and then broadcasts them so they can be picked up by an ANT receiver.

For my project I chose the Garmin Soft Strap model HRM2-SS which I found on Amazon for $44.

ANT Modules

I started by purchasing Sparkfun’s USB ANT Stick.  This was a very nice module because it got me both a USB interface that could be plugged into a PC.  Also the board broke out power, ground, transmit and receive which facilitated connecting them to a microprocessor.  Unfortunately, shortly after I purchase this from Sparkfun they discontinued the product with no replacement.

I also ordered a Dynastream Innovations ANT11TS33M4IB Module as I felt the form factor of this module would work better in the final design.  The Dynastream module is I purchased is the module on the ANT website that is recommended for prototyping. It can be purchased from several sources. I purchased mine from Digikey.

Next Steps

My plan for moving forward is to start by interfacing the ANT modules with an Arduino.  Once I have done this I plan to leverage the Circuits@Home USB Host Shield that I purchased and tested out last spring to interface with Android.

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