🛠 Interroger un capteur I2C sur le connecteur 40 broches

Objectives

Connect an I2C sensor or peripheral (OLED SSD1306, BME280, CO2 sensor…) to the 40-pin connector of the ROCK 3B and detect it with i2c-tools. The official documentation lists 3 I2C controllers on the connector (header function table); the exact pins depend on the muxing of your hardware revision — the number of functions varies between the CNX launch sheet and the current documentation, so we verify on the board.

Hardware

• Radxa ROCK 3B running Radxa OS (or mainline ≥ 6.11 with overlays enabled)
• 3.3 V I2C sensor (SSD1306 at 0x3c, BME280 at 0x76/0x77)
• 4 Dupont wires: 3.3 V, GND, SDA, SCL (identified by the connector's color code, official plan at docs.radxa.com)

Complete code

sudo apt install i2c-tools
# Activer le contrôleur I2C du connecteur (Radxa OS : outil rsetup)
sudo rsetup    # Interface/Overlay settings -> activer l'I2C du header, reboot

sudo modprobe i2c-dev
i2cdetect -l                     # lister les contrôleurs i2c-0, i2c-1...
# Identifier le bus du connecteur via le device tree :
for d in /sys/bus/i2c/devices/i2c-*; do
  echo "$d : $(cat $d/of_node/fullname 2>/dev/null)"; done
sudo i2cdetect -y N              # N = bus du connecteur repéré ci-dessus
sudo i2cget -y N 0x76 0xd0       # exemple : ID du BME280 -> 0x60

Expected verification

i2cdetect -y N displays a grid where the sensor's address appears (3c, 76, 77…); i2cget returns a consistent value (0x60 for the BME280). No UU if no kernel driver already claims the module.

Common errors

• Scanning the wrong bus: the RK809 PMIC (audio/power) sits on an internal bus, not on the connector — use of_node/fullname to find the bus wired to the header.
• I2C disabled by default: without an enabled overlay (rsetup under Radxa OS, &i2c2 status="okay" in mainline), i2cdetect -l shows nothing matching the connector.
• Relying on a pinout inherited from the ROCK Pi 4 or an old wiki: Radxa's documentation itself has evolved between revisions (Revision Details page) — check the V1.51 schematic of your board.
• Powering a 5 V module whose logic pins are not 5V-tolerant: stay at 3.3 V on this board.
• Two modules at the same address: plan for a TCA9548A multiplexer or shift the address (ADR).