Are you going to a dance party soon? Or maybe a speed dating night? Would you like to wear your heart out?

In this project, you can visibly show off your heart rate in the form of a pulsing pendant. A Circuit Playground Bluefruit (CPB) connects to a heart rate monitor to display the heartbeat of the wearer. Using the CircuitPython programming language, the CPB blinks with red NeoPixels to display the heart rate. 

The Circuit Playground Bluefruit will be referred to as the "CPB" for the remainder for this guide.


Heart Rate Monitor

You'll need a heart rate monitor that supports Bluetooth Low Energy (BLE). I'm using the Scosche RHYTHM+ but you should be able to use any monitor that uses the Bluetooth SIG Heart Rate service standard.

These work by flashing green (and sometimes yellow) LEDs against your skin and then measuring the reflected light that returns. The color changes/darkens during the pulse of your heart thanks to all that blood sloshing around!

shot of a Black woman's neon-green manicured hand holding up a Circuit Playground Bluefruit glowing rainbow LEDs.
Circuit Playground Bluefruit is our third board in the Circuit Playground series, another step towards a perfect introduction to electronics and programming. We've...
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Option 1: you can use a small Lithium Ion Polymer or "Lipo" battery and affix it to the back of the CPB.

Lithium Ion Polymer Battery 3.7v 420mAh with JST 2-PH connector and short cable
Lithium-ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light, and powerful. The output ranges from 4.2V when completely charged to 3.7V. This...
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Option 2: If you want to avoid lipos, you can use x3 AAA batteries with a battery back to get the same 3.7V to power the CPB.

Front angled shot of 3 x AAA battery holder with on-off switch and 2-pin JST PH connector.
This battery holder connects 3 AAA batteries together in series for powering all kinds of projects. We spec'd these out because the box is slim, and 3 AAA's add up to about...
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Angled shot of 3 PKcell AAA batteries.
Battery power for your portable project! These batteries are good quality at a good price, and work fantastic with any of the kits or projects in the shop that use AAA's. This is a...
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Optional Enclosure

There's a great case for the CPB that also works for the Circuit Playground Express (CPX). It is not required for this project but helps to make the NeoPixels a little more glowy and provides protection for the electronics.

Top down view of a clear acrylic Adafruit Circuit Playground Express or Bluefruit Enclosure.
We've got nice cases for many of our beloved boards, but the Circuit Playground Express and
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Other materials

  • A lanyard or string for the pendant.
  • double-sided tape for the battery.
Using metal or other conductive-based material for the lanyard may result in shorting the CPB causing the project to not work properly. Try using a material like plastic or a textile-based fabric like yarn.

This guide was first published on Jan 25, 2022. It was last updated on Jul 14, 2024.

This page (Overview) was last updated on Mar 08, 2024.

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