You may use any non-conductive material for the lanyard if you choose to string it through the holes of the CPB as shown in this guide. Yarn, hemp, twine, and plastic are all great materials that are easy to string through the CPB holes and tie into a necklace for easy wearing.
If you wish to use a conductive material for the lanyard such as a metal chain, you must ensure the material does not touch the CPB or you risk shorting the circuit and causing the CPB the malfunction or worse. One idea is you could use hot glue to glue the chain to the CPB plastic case. Be sure to use Kapton tape over the CPB pinholes to avoid a short.
You may want to enclose the CPB but it is not required. If you use the Adafruit Circuit Playground case, follow these steps to make sure the case fits properly:
- Place the CPB on top of the bottom piece of the case.
- Place the top of the case over the CPB, making sure the pins on the CPB align with the pins labeled on the case.
- Make sure to align the switch on the CPB with the case's switch.
- Firmly press both the top and bottom of the case. You should feel a click as the case is snapped into place.
- If the case is not firmly snapped into place, try applying pressure to the case on the JST plug side as well as the USB micro b side.
You can use either a Lipo battery or a AAA battery pack with x3 AAA batteries to power the CPB and make it mobile. Just use some double-sided tape to affix the power source to the back of the CPB case (or the CPB itself if you are omitting the case).
That's it! Now go out there and show off your neat heart beat. Wear it loud, wear it proud.
This project was inspired by Sidney San Martín's Heart Rate Collar build. Additionally, it uses a similar concept from Becky Stern's Heart Rate Badge guide. John Park's CircuitPython BLE Heart Rate Zone Trainer Display, was a huge help for the BLE connection code.