<\/p>\n
The Solution<\/h2>\n
Rather than wait for my CABLE to fail, and having to replace my perfectly working spinning bike because of this, I wrote my own ANT+ to Bluetooth bridge in Go. This runs on Debian with a USB ANT+ dongle. The architecture is straightforward. An Ant module receives ANT+ events and puts them on a Channel from where the Bluetooth module reads them:<\/p>\n
\nhide footbox
\nskinparam sequenceArrowThickness 2
\nskinparam actorStyle hollow<\/p>\n
skinparam arrow {
\n FontSize 10
\n}
\nskinparam note {
\n FontSize 10
\n}<\/p>\n
actor “Trainer” as Trainer
\nparticipant “ANT+\\nModule” as ANT
\nparticipant “Event\\nChannel” as Channel
\nparticipant “BLE\\nModule” as BLE
\nactor “Zwift” as Zwift<\/p>\n
activate ANT
\nactivate Channel
\nactivate BLE<\/p>\n
Trainer -> ANT : broadcast\\nANT+ raw data
\nnote over ANT: Parse ANT message,\\nextract payload<\/p>\n
ANT -> Channel : write\\n(RPM, Power, Time)
\nChannel <- BLE : read\\n(RPM, Power, Time)
\nBLE -> BLE: process to\\n(NREV, TREV, Power)
\nBLE -> Zwift: send\\n(NREV, TREV,\\nPower)
\n\" usemap=\"#plantuml_map\"><\/p>\n
The key challenge: ANT+ broadcasts instantaneous RPM, while Bluetooth requires cumulative revolution counts and a last-revolution timestamp.<\/p>\n
Technical Challenges<\/h2>\n
Three issues required custom solutions:<\/p>\n
- \n
- USB reliability<\/strong>: The ANT+ library’s USB handling wasn’t robust enough, so I wrote my own to support hot-plugging the dongle.<\/li>\n
- Recovery from bicycle pauzes<\/strong>: When the bike stops transmitting (e.g. during a break), the bridge now detects 10 seconds of inactivity and reinitializes automatically. Without this it did not recover.<\/li>\n
- Restarts or crashes of the bridge<\/strong>: When the bridge restarts it resets the bluetooth interface. This causes the bike to automatically reconnect. There must be a proper way to do it but life is too short to find out.<\/li>\n
- Crash robustness<\/strong>: A script runs the bridge and simply restarts it when it crashes. Crashes still can occur occasionally although haven’t seen them while cycling.<\/li>\n
- Sleep prevention<\/strong>: Wrapped the bridge in
systemd-inhibit<\/code> to prevent the PC from sleeping mid-ride:
\nsystemd-inhibit --what=idle:sleep --why=\"Do not interrupt cycling\" $( dirname $0 )\/bin\/bridge \"$@\"<\/code><\/li>\n<\/ul>\nPhysical challenges<\/h2>\n
During initial development I was a lot on the bike trying to get the ant+ data to show. After development I was still a lot on the bike.<\/p>\n
Conclusion<\/h2>\n
The bridge has been running reliably across sessions from 30 minutes to over 2 hours. The code is available here<\/a> and supports ANT+ dongles that identify as “Dynastream Innovations”. It’s not perfect, but it works well \u2014 pull requests welcome.<\/p>\n","protected":false},"excerpt":{"rendered":"
As a regular Zwifter, I use a Life Fitness IC5 spinning bike (2020) that broadcasts power and cadence over ANT+. The Problem Modern devices only support Bluetooth, requiring an ANT+ bridge such as the North Pole Engineering CABLE or the … Continue reading
- Recovery from bicycle pauzes<\/strong>: When the bike stops transmitting (e.g. during a break), the bridge now detects 10 seconds of inactivity and reinitializes automatically. Without this it did not recover.<\/li>\n