So, this hasn’t worked out quite how I anticipated so far, I’ll have to give it another go later.

You might have seen the hrv_monitor board in a picture I linked a while back – It is intended to be a simple reflective heart rate monitor. At the moment I’m unclear if I’ve badly underestimated how much accuracy I need, or if there’s some other problem with what I did that is more fixable in software…

I built a simple software stack hoping to get some data demonstrating that the device works; and what I’ve found is that the device makes a great near-range reflective rangefinder, but it’s not showing any trace of a heartbeat in my data.

So far what has been done is:

  • There’s code for the microcontroller which runs on a timer and collects ADC data 100 times a second. If the PC software is connected, it will send that data over USB.
  • I built a simple demo app which indicates its presence to the uC, and receives and graphs the data, image below. The black trace is the “dark” measurement value with no LEDs on, and the other 4 lines are the ADC values measured with each of the LEDs lit, in turn.


So well, not everything works on the first try, I certainly don’t claim to be an expert in this kind of biometric sensor and this was a very quickly thrown together side project based on assumptions and not research. Maybe I’ll still get it working though, another time – Too many other projects need attention for now.

In case anyone else is interested, the code and design files related to this project are here: