GPIO Pin Map Reference

Overview

This is the consolidated pin reference for the beacon. It brings together the radio, GPS, OLED, buttons, status LED, and any other GPIO the firmware uses, in one place. Use it when wiring the board or checking a clone layout.

Pin numbers follow the ESP32 package used on the dev board. Not every dev board maps pins identically; confirm against your board’s silkscreen.

Full Pin Table

Function	GPIO	Direction	Notes
Radio SCK	18	output	SPI clock
Radio MISO	19	input	SPI MISO
Radio MOSI	23	output	SPI MOSI
Radio CS	5	output	chip select
Radio RST	14	output	reset
Radio BUSY	21	input	must be wired
Radio DIO1	2	input	RX/TX events
Radio TCXO	—	power	1.6V if present
GPS TX	12	output	ESP TX to GPS RX
GPS RX	22	input	ESP RX from GPS TX
GPS VCC	3.3V	power	3.3V only
OLED SCK	15	output	SPI clock for OLED
OLED SDA	13	output	SPI MOSI for OLED
OLED RES	4	output	reset
OLED DC	16	output	data/command
OLED CS	17	output	chip select
SW_MODE	33	input	mode button
SW_SEL	32	input	select button
SW_UP	35	input	up button
SW_DN	34	input	down button
Status LED	—	output	onboard or external
Battery ADC	—	input	battery voltage read

A few pins are labeled with their function rather than a fixed number where the implementation uses a board-specific pad or an onboard resource. Confirm on your schematic.

Direction Notes

• GPIO 34 and GPIO 35 are input-only on many ESP32 packages. That is why the down button is on 34 and the up button is on 35: they only need to read a press.
• GPIO 22 is used for GPS RX on the current firmware because it works as an ESP TX on the chosen UART. Earlier prototype wiring put the GPS RX on 34, which caused a pin-side error; the current assignment fixes that.
• The radio BUSY pin is input-only in function but must be connected to a real GPIO so the library can read it.

SPI Bus Separation

The beacon uses two SPI buses:

• The radio uses SPI on the pins in the table above.
• The OLED uses its own SPI pins, separate from the radio.

This keeps the OLED from interfering with the radio during TX. Do not share the radio’s SPI pins with the OLED.

UART Separation

The GPS uses UART2, separate from the USB serial console. This keeps GPS NMEA data off the debug console and lets the USB serial remain available for logging.

Button GPIOs

The four buttons use the GPIOs in the table. Their firmware behavior is:

• SW_MODE on 33.
• SW_SEL on 32.
• SW_UP on 35.
• SW_DN on 34.

If you clone the board, keep these assignments unless you also update the firmware pin definitions.

Safety Notes

• Do not drive 5V into a 3.3V pin.
• Do not leave the radio BUSY pin floating.
• Keep the GPS power at 3.3V.

Related Pages

• GPIO Pin Map — the board-level pin mapping.
• Wiring & Connectors — how to make the connections.
• NEO-6M GPS Module — GPS pin details.
• Radio Library and SX1262 — radio pin details.