Hardware / GPIO Map

Pin assignments for PCB rev 6.3 / factory firmware 2.9.2 (see Device Overview). A different PCB revision could wire things differently. Items marked unconfirmed have not been measured on a unit.

Outputs

GPIO	Role
GPIO9	valve driver input A
GPIO10	valve driver input B
GPIO40, 39, 41, 42	the four LEDs (which is which is unconfirmed)
GPIO15, GPIO2	unidentified outputs, probably the second driver IC's inputs (unconfirmed)

Inputs

GPIO	Pull	Active level	Role
GPIO6	pull-up	low	front button: wakes the unit and keeps it awake (also a wake pin)
GPIO17	pull-up	low	unidentified; a press appears to restart the unit (long press does something else), probably an external key pad (unconfirmed)
GPIO13	pull-up	low	bottle eject switch (also a wake pin)
GPIO7	pull-up	low	float switch (also a wake pin)
GPIO16	pull-down	high	external power sense (also a wake pin)
GPIO18, GPIO19, GPIO20	pull-up	n/a	hardware-variant straps (below)

Pulls are what the board design expects; the active level follows from the pull (the idle level is the pulled level) and is unconfirmed on a unit. Wake behavior is on Power and Sleep.

Hardware variant straps (GPIO18 / GPIO19 / GPIO20)

Three pins select the valve variant: id = g18 + 2*g19 + 4*g20.

• 0 (all low): simple valve, no feedback.
• 7 (all high): latching valve with position feedback.

Other values leave the valve drivers unused. The straps look like external resistors on the PCB, so a unit's variant can be read off the board or by reading the three pins. GPIO19/20 are also the S2's native-USB pins.

Valve driver

• Simple valve: open = GPIO9 low + GPIO10 high; closed = both low.
• Latching valve: the same pins are driven with short reverse pulses, with a feedback line polled for about 700 ms after each move and one retry if it is slow. This points to a motorized valve with position or stall feedback. The ESPHome config does not implement it.

A dispense runs: battery check, count the start, valve open, hold for the dose time, valve closed, count the finish.

Battery

The battery is sensed on ADC1 channel 7 = GPIO8 at 11 dB attenuation. A good reading is the average of 16 samples converted to millivolts with the ESP-IDF calibration, then multiplied by about 3.02 (the divider ratio; unconfirmed, measure the battery and the BAT_ADC pad). The battery range is 2200 to 3000 mV; the unit treats 20% as low and 10% as critical, and blocks dispensing below 20%.

Dose time

The dose time is probably counted in tenths of a second (unconfirmed).