This GATT server uses acceleration data from the ADXL345 to provide a Running Speed and Cadence service which works with Zwift.
- Raspberry Pi Zero W / WH installed with (at least) Raspbian Buster Lite
- ADXL345 accelerometer connected to Raspberry Pi
- Elliptical trainer or similar (tested with New Image Maxi-Glider 360)
- Power source (e.g. USB power bank)
Older versions of Raspbian may work but they will most likely require to have Bluez updated. The code may also work perfectly well on a different model of Raspberry Pi with a BLE dongle.
The accelerometer should be attached to one of the footrests and oriented in such a way that the acceleration is detected on the X-axis. (For both models of ADXL345 I have tried - one with pins at both ends, and one with a single row of pins - the pins should be parallel with the footrest.) I also have the Pi taped securely to the underside of the footrest along with a nano-suction power bank.
(Optionally) update the Pi:
apt-get update
apt-get dist-upgrade
Install the required packages:
apt-get -y install python3-pip
pip3 install adafruit-circuitpython-adxl34x
Place pielliptical.py in /usr/local/bin and make it executable:
mv pielliptical.py /usr/local/bin
chmod 755 /usr/local/bin/pielliptical.py
Using raspi-config enable I2C under Interfacing Options. I also set Desktop / CLI to Console under Boot Options, and Memory Split to 16 under Advanced Options as I don't require a graphical login. The Pi will need to be rebooted for these changes to take effect.
Run /usr/local/bin/pielliptical.py to test the script and verify that the device shows up (probably as raspberrypi followed by a number) within Zwift when searching for a Run Speed device. It can take a few seconds for initial detection. The raspberrypi device does not need to be calibrated within Zwift.
The device has been tested successfully with the following configurations:
- Zwift on Windows 10 + Zwift Companion on Wileyfox Swift 2X running LineageOS 15.1
- Zwift on Windows 10 + Zwift Companion on Amazon Fire 7 running LineageOS 14.1
- Zwift on Wileyfox Swift 2X running LineageOS 15.1
To have the service run automatically on boot, edit /etc/rc.local and insert the following before exit 0:
/usr/local/bin/pielliptical.py > /dev/null 2>&1
I also added tvservice --off above this line as I don't need HDMI output.
If the raspberrypi device still hasn't shown up in Zwift after a minute or so, try killing Zwift Companion entirely and restarting it, or restarting the Android device it is running on. (BLE seems to be less reliable than ANT+ in this regard.)
- Configure Pi to run entirely in read-only mode so it can be powered off safely
- Disable wi-fi entirely for faster startup
It should be possible to complete running workouts successfully with a minimum of practice.
I estimated that a cadence of 120 steps per minute was equivalent in effort to a 6-minute mile. It is suitably hard to maintain for a long period of time, even if it is easier than actually running due to the non-impact nature of an elliptical trainer. A simple formula is applied to the detected cadence to make it look more like an actual running cadence.
- There is probably something wrong with the Bluetooth advertisement, since the Pi cannot be detected in Zwift on Windows using a Bluetooth adapter, and is slow to be detected from Zwift on Android or via Zwift Companion.
The code in this repository is based on code taken from the BlueZ project. It is licensed under GPL 2.0.