My Decathlon Domyos bike measures power and cadence and sends it over Bluetooth FTMS. My Apple Watch can record power, but only from Cycling Power sensors. Different protocol, so my indoor rides had heart rate and nothing else.

I made this thing where the ESP works as a BLE connector, gets data from the Bike and sends it to my apple watch with different protocol that apple watch can read. That way no additional apps needed, and everything ends up in apple health.

Why the ESP32-C3 (Super Mini)

- It only needs BLE, and the the C3 does have it, also it's the smallest so you could hide it better if you get power from the bike to it

- Native USB, no USB-UART chip. That made browser flashing easy

- About 3€, small, onboard LED for status.…