Cadence controlled LED bike lights

I built some cadence controlled LED bike lights this week to put on my bike for this weekend’s Dunwich Dynamo – an annual overnight cycle ride from London to the coast.

Here is a quick demo of the thing in action:

Hardware

The cadence on the bike is measured by a Wahoo fitness cadence sensor, which detects each time the pedal passes it, as a magnet is fitted to the pedal. The Wahoo fitness sends a signal wirelessly via the ANT+ protocol, typically used for bike computers to display the info on the handlebar.

I used a Raspberry Pi computer with a Suunto USB Ant-stick to pick up the ANT+ signal, and also a Wifi USB dongle so that I could VNC from my phone into the Raspberry PI to make tweaks whilst I was on the ride.

The LED light itself was a strip I’d bought off of eBay.

I used an 13,000mAh Anker battery pack to supply power to both the Pi and the LED strip light.

Software

The code was based on:
Python ANT library – https://github.com/mvillalba/python-ant/
Tom Wardill’s HRM code – https://github.com/tomwardill/developerhealth
Haotianwooo’s Cadence code – https://github.com/haotianwooo/ant_raspberry/blob/master/only_cadence.py
Bibliopixel LED library – https://github.com/ManiacalLabs/BiblioPixel/

Implementation

The LEDs and Pi were wired up as follows:

Pi 5V – 5V on USB powers supply, +5V on LED strip
Pi MOSI – DI on LED strip
Pi SCLK – CI on LED strip
Pi GND – GND on USB power supply, GND on LED strip

Reference: https://learn.adafruit.com/raspberry-pi-spectrum-analyzer-display-on-rgb-led-strip/led-strip-and-rgb-led-software

To get the Suunto USB stick up and running, follow: https://www.johannesbader.ch/2014/06/track-your-heartrate-on-raspberry-pi-with-ant/

Install Python-ANT and the Bibliopixel LED library

I set it to run automatically when the Pi boots up, and installed TightVNCServer so I could log into in from my phone (set up phone tethering as a known wi-fi network on the Pi).

It worked well on the night, and the battery pack lasted the distance – it went from 100% to ~50% over the 11½ hours it was switched on.

My code used on the night ride can be found here: https://github.com/jimlondon/cadence-led/