ArduRower

The project was created on the basis of the ESP32 board (Heltec WiFi Kit 32 - cheap ESP32 board with OLED & LiPo battery interface) for equipping chinese clones of waterrower like Incline, XtremepowerUS, Hunter, Fit-On or DIY rowing machines with a 0.96-inch OLED screen and bluetooth interface. The device have emulates the work of the original WaterRower S4 equipped with a bluetooth comm module. Tested work with the Coxswain app, which allows to record and export your workouts to Garmin Connect and/or Strava, work with Kinomap, HOLOFIT and probably other applications that support the FiTness Machine Service protocol better known as FTMS. To connect to your rowing machine, you only need to attach two GND and GPIO2 wires to the RPM sensor (you can add 1kΩ resistor or similar on each wire for protection ESP32 board). You can also connect the battery to GPIO33 through a divider of two resistors: 220kΩ resistance connects to "+" of LiPo battery and GPIO33, 100kΩ resistance to GND and GPIO33

It is possible to write directly to the Garmin Connect using the Connect IQ DataField ArduRower-IQ https://apps.garmin.com/en-US/apps/0e10bae1-9753-4915-b856-040d0cbdd82a

Rower side based on sketch WaterRino: https://github.com/adruino-io/waterrino
Bluetooth side on sketch WaterRower S4BL3 Bluetooth BLE for S4: https://github.com/vibr77/wr_s4bl3_samd