BLE Wireless Heart Rate Collector
Putting these together, along with custom software I wrote, I was able to make the wireless heart rate collecting device as shown below.
The Nordic dev board comes with a lithium coin cell battery for wireless use. The animated gif below shows the heart rate collector while I'm wearing the heart rate monitor chest strap.
The code for this project can be found on my GitHub repo here. The nRF5 SDK includes a heart rate collector example. I modified it to create this project. I used Segger Embedded Studio for all firmware development and debugging.
Probably the most time consuming part of this project was getting the Adafruit display to work with the nRF52840 development board. Adafruit has a GitHub repo with code for getting the display to work with an Arduino. I had to rework this quite a bit for the nRF52840 dev board.