Adds an interface for the Virtufit water resistance row 1000 rowing machine to provide custom stats.
Electrical Interface
Two magnetic sensors configured for quadrature encoding of direction and velocity. The cable spool has two magnets on it and provides around nine data points on each stroke.
The sensors are connected to a 3.3V input pullup and pull the line low when the magnet passes it. There is a glitch when the magnet is directly underneath, which can cause issues at low speed and requires a debounce filter on the input.
Software Interface
Serial 115200 baud, prints columns of data.
Data Schema
A row is recorded at the end of each tick (after a magnet has passed the second sensor).
workout_time_usec
Time since beginning of workout.
stroke_time_usec
Time since beginning of current stroke.
tick_duration_usec
Time it took for the magnet to pass from one sensor to the next (from falling edge on sensor A to falling edge of sensor B of the electrical signal). Positive values are produced during the drive, and negative during the recovery.
inst_power
Instantaneous force exerted on the handle. Calculated by the speed of the belt squared, with the speed of the belt being calculated as the inverse of the tick duration.
stroke_power
Integral of the drag forces for current stroke, calculated here with a running sum for simplicity.
inst_spm
Approximation of strokes per minute based on speed of previous stroke.
BLE FTMS
TODO.