🛠 Lire un capteur I2C (Weather Board Zero)

Objectives

Enable the I2C bus on the ODROID-C4 under Armbian mainline and read a BME680-type environmental sensor (Hardkernel Weather Board Zero, ~$2): address detection with i2cdetect, register reading in Python via smbus, and declarative activation of overlays in armbianEnv.txt.

Hardware

• ODROID-C4 running Armbian current (kernel 6.6)
• Weather Board Zero (or any BME-class sensor in an I2C module) — 40-pin connector, 3.3 V logic
• sudo apt install -y i2c-tools python3-smbus device-tree-compiler
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Full code

# 1) Activer I2C (Armbian) puis redémarrer
sudo sed -i 's/^#*overlay_add=.*/overlay_add=i2c0/' /boot/armbianEnv.txt
sudo reboot
# 2) Détecter le capteur
i2cdetect -l        # lister les bus
i2cdetect -y 0      # le capteur répond à 0x76 ou 0x77

#!/usr/bin/env python3
# lecture_bme.py - CHIP_ID + température brute (démo non calibrée)
import smbus, time
BUS, ADDR = 0, 0x77   # adapter selon i2cdetect
bus = smbus.SMBus(BUS)
chip_id = bus.read_byte_data(ADDR, 0xD0)
assert chip_id == 0x61, f"chip id inattendu {chip_id:#x}"

def read_reg24(reg):
    msb, lsb, xlsb = bus.read_i2c_block_data(ADDR, reg, 3)
    return (msb << 12) | (lsb << 4) | (xlsb >> 4)

while True:
    t = read_reg24(0x24) / 16384.0 - 50.0
    print(f"température brute ≈ {t:6.2f} °C (CHIP_ID={chip_id:#04x})")
    time.sleep(2)

Expected verification

i2cdetect -y 0 displays a grid with a non-empty cell at 0x76 or 0x77. The Python script prints a temperature line and the CHIP_ID 0x61 every 2 seconds; Ctrl+C stops it cleanly. The raw value is approximate (demonstration without BME680 calibration table) but should change when you warm the sensor with your finger.

Common errors

• OSError: [Errno 121] Remote I/O Error: wrong address or bus — recheck the i2cdetect output, test -y 1.
• No bus listed: the i2c0 overlay is not enabled in /boot/armbianEnv.txt or the machine has not rebooted.
• Trying to read the connector's ADCs at the same time: ADC inputs are limited to 1.8 V maximum, not 3.3 V!
• Plugging in the Weather Board while powered on: turn off the power before connecting a module to the 40-pin connector.
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