GPIO Pin Reference

Complete pin assignment table using BCM (Broadcom) numbering:

BCM Pin	Direction	Function	Connects To
17	Output	Select S0	S0 on all 6 muxes
27	Output	Select S1	S1 on all 6 muxes
22	Output	Select S2	S2 on all 6 muxes
23	Output	Select S3	S3 on all 6 muxes
	Input	Mux 0 SIG	Black storage zone
7	Input	Mux 1 SIG	Board files a–b
8	Input	Mux 2 SIG	Board files c–d
9	Input	Mux 3 SIG	Board files e–f
10	Input	Mux 4 SIG	Board files g–h
11	Input	Mux 5 SIG	White storage zone
	I2C	OLED SDA	OLED display data
3	I2C	OLED SCL	OLED display clock
	Input	Start button	Active-low, pull-up enabled
21	Input	Stop button	Active-low, pull-up enabled
24	Input	Reset button	Active-low, pull-up enabled

All GPIO pin assignments for sensors and operator UI

Note

The mux pin assignments can be overridden by passing custom arrays to the BoardScanner constructor. The button defaults are defined in button_controller.h; the OLED defaults are defined in display_controller.h. If you need to change them, update the corresponding default constants and rebuild.

Raspberry Pi Header Pin	BCM GPIO
Pin 11	GPIO 17 (S0)
Pin 13	GPIO 27 (S1)
Pin 15	GPIO 22 (S2)
Pin 16	GPIO 23 (S3)
Pin 3	GPIO 2 (OLED SDA)
Pin 5	GPIO 3 (OLED SCL)
Pin 7	GPIO 4 (Mux 0)
Pin 26	GPIO 7 (Mux 1)
Pin 24	GPIO 8 (Mux 2)
Pin 21	GPIO 9 (Mux 3)
Pin 19	GPIO 10 (Mux 4)
Pin 23	GPIO 11 (Mux 5)
Pin 38	GPIO 20 (Start button)
Pin 40	GPIO 21 (Stop button)
Pin 18	GPIO 24 (Reset button)

BCM to physical header pin mapping

Warning

Do not confuse BCM GPIO numbers with physical header pin numbers. The mux SIG inputs now use replacement GPIOs 4, 7, 8, 9, 10, 11 on physical header pins 7, 26, 24, 21, 19, 23. These pins overlap the Raspberry Pi SPI alternate function, so keep SPI disabled or unused for this wiring test.