Giving a PICAXE a heart beat

hippy

Technical Support
Staff member
Going one step beyond having a LED flash to show 'it's alive' - why not have a PICAXE send data to a heart rate monitoring watch ?

I just happened to find one of these ...

https://activekids.sainsburys-live-well-for-less.co.uk/active-kids-products/product/S4A00227

No chest strap which it needs to operate but I guessed (more hoped) it expected a burst of 5kHz radio signal each heart beat as many analogue HRM chest straps generate. So, a quick bit of coding, and, bingo, "79" displayed just like the photo, the heart icon flashes on each 'pulse' ...

Code:
#Picaxe 28X2
Do
  PwmOut PWMDIV4, C.1, 99, 200 ; 5 kHz
  Pause 100
  PwmOut C.1, OFF
  Pause 660
Loop
For a transmitting aerial I used ~250m of twisted pair blue/yellow telecom wire left coiled on its drum, connected one wire to output pin C.1, left everything else unconnected, placed the watch in the middle core of the drum. You'll probably want to miniaturise that if making your own HRM chest strap :)

Seems to work with any pulse burst longer than 10ms. Ran at 5V for maximum power but signal strength is minimal, just a couple of centimetres and needs to be on the axis of the coiled up cable. Still, impressive it even worked at all.

Could be the basis of a useful tool if you have a HRM setup and are not sure if it's the watch or chest belt which has died and could probably be modded to generate a coded signal as Polar and others use.
 
Top