Raspberry Pi Cycle Computer

This is a simple script to use a Raspberry Pi's GPIO pins in conjunction with a reed switch to create a simple cycle computer, which will write stats out to an InfluxDB instance.

It was created with an exercise bike in mind: I have an under-desk setup and it was bugging me that I couldn't see how much use I actually make of it, so I decided to build a replacement cycle computer

Pre-Requisites

It's assumed that you already have

A Raspberry Pi (I prototyped on a 3 and then then used a Zero 2W)
Installed an OS and configured connectivity on your Pi (examples)
Installed the RPi.GPIO library

Setup Instructions

Install Telegraf

curl --silent --location -O \
https://repos.influxdata.com/influxdata-archive.key \
&& echo "943666881a1b8d9b849b74caebf02d3465d6beb716510d86a39f6c8e8dac7515  influxdata-archive.key" \
| sha256sum -c - && cat influxdata-archive.key \
| gpg --dearmor \
| sudo tee /etc/apt/trusted.gpg.d/influxdata-archive.gpg > /dev/null \
&& echo 'deb [signed-by=/etc/apt/trusted.gpg.d/influxdata-archive.gpg] https://repos.influxdata.com/debian stable main' \
| sudo tee /etc/apt/sources.list.d/influxdata.list
sudo apt-get update && sudo apt-get install telegraf

Add the telegraf user to the gpio group

adduser telegraf gpio

Clone this repo down and move into place

git clone https://github.com/bentasker/wifi_cycle_counter.git
sudo mv wifi_cycle_counter /usr/local/src/

Config

The easiest way to get started is to copy config/telegraf.conf.example to /etc/telegraf/telegraf.conf and then edit it

sudo cp /usr/local/src/config/telegraf.conf.example /etc/telegraf/telegraf.conf
sudo nano /etc/telegraf/telegraf.conf

You will need to

Update the plugin config section to provide the path to count.py (if you installed in a different location)
Update the output section with details of your InfluxDB instance

Starting

Once you're ready, you should just need to restart Telegraf (note: not reload - we need Telegraf to pick up the new group)

systemctl restart telegraf

Config Vars

The script has a range of configuration vars, each of which can be set in the environment section in Telegraf's config

GPIO_NUM: which GPIO should we bind to (default is 4: pin 7)
CYCLES_PER_CALORIE: how many rotations per calorie (default 7)
POLL_INTERVAL: How often should the script calculate how many rotations have happened? (default 5)
WRITE_INTERVAL: How often should the script write out a set of stats (should be >= POLL_INTERVAL, default 30)
WRITE_NO_CHANGE: Should we write a point even if there have been no rotations (default true)
CALCULATE_DISTANCE: Should we calculate distance and speed?
WHEEL_RADIUS: What wheel radius (in cm) should we use to calculate distance/speed (default 5.6)
SPEED_FORMAT: What unit should we use for speed (mph, kph, cm/s. Default mph)
INFLUXDB_MEASUREMENT: InfluxDB measurement to use in generate line protocol (default: "cycle_activity")
INFLUXDB_EXTRA_TAGS: Additional tags to inject into line protocol (default: "". Example "foo=bar,sed=zoo")
PRECISION: Number of decimal places to include in floats

Visualisation

An example Grafana dashboard is provided.

bentasker/wifi_cycle_counter