Summary
If you spend any time near a gym, you may be familiar with Bluetooth heart rate monitors — a small pack of electronics mounted on a strap round the chest which can relay heart rate data to an external logger or display. We’re pleased to see [Milos Rasic]’s project then, an open-source version of one of those monitors. The heart rate capture is done by an AD8232, while the Bluetooth part is handled by a Seeed Studio XAIO ESP32 board. Power is provided by a single 3.7 V cell, with a boost converter to push that up to 5 V. The design omits a charge controller to keep things simple, so figuring out how to top off the cell is left as an exercise — no pun intended — for the user. Software is loaded through the Arduino IDE, which raises the possibility that other ESP32 CPUs could be supported with a bit of modification. All in all it’s a surprisingly simple project, and while the manufactured version is cheap enough it’s still very much worth having one that’s open source. If you’d like to know more about his quest to develop open medical devices, check out the talk [Milos] gave on the intricacies of blood pressure monitoring earlier this year at Hackaday Europe. I have seen a guy shortly after he had had open heart surgery, so no matter what rate it monitors, I think I’d rather keep my chest closed, thank you 😜 I wonder if it need 10 or 100x times more power compared with a Polaris H10. :-D I’m also surprised people choose ESP32 for battery powered projects. The nRF52 MCUs uses a lot less energy, has built in buck converter and they have an example of a simulated HRM in their SDK. There are plenty of modules to buy for them too. An nRF54L will draw even less, but I don’t remember if it can run directly from the battery.