🛠 Lire un capteur I2C (BME280 température/humidité)

Objectives

Enable the I2C bus on the Raspberry Pi 5, detect a BME280 environmental sensor (temperature, humidity, pressure), and read its measurements in Python. On the Pi 5, I2C is provided by the RP1 chip; the main I2C0 bus is on GPIO2 (SDA, physical pin 3) and GPIO3 (SCL, physical pin 5).

Hardware

• Raspberry Pi 5 running 64-bit Raspberry Pi OS
• BME280 sensor in an I2C module (address 0x76 or 0x77)
• Dupont cables: SDA to pin 3, SCL to pin 5, VCC to 3V3 (pin 1 or 17), GND to pin 6
• The module has built-in pull-up resistors; the pins operate at 3.3 V logic levels

Complete Code

# 1) Activer I2C : sudo raspi-config -> Interface Interfacing Options -> I2C
#    ou dans /boot/firmware/config.txt : dtparam=i2c_arm=on
sudo apt install -y i2c-tools python3-smbus
sudo reboot

# 2) Vérifier la présence du capteur (0x76 ou 0x77 attendu)
i2cdetect -y 1

#!/usr/bin/env python3
# lire_bme280.py — lecture brute des registres du BME280 sur I2C bus 1
import smbus, time

BUS = smbus.SMBus(1)
ADDR = 0x76   # 0x77 si les broches SD0/AD0 sont câblées autrement

def read_regs(reg, n):
    return BUS.read_i2c_block_data(ADDR, reg, n)

# Calibration (une seule fois au démarrage)
dig = read_regs(0x88, 24) + read_regs(0xE0, 7)
BUS.write_byte_data(ADDR, 0xF2, 0x01)              # oversampling humidité
BUS.write_byte_data(ADDR, 0xF4, 0x27)              # mode normal
BUS.write_byte_data(ADDR, 0xF5, 0x00)
time.sleep(0.5)

while True:
    data = read_regs(0xF7, 8)                       # T, P, H bruts
    print("octets bruts T/P/H :", [hex(b) for b in data])
    time.sleep(2)

Expected Verification

i2cdetect -y 1 displays a box at 76 (or 77). The script displays the raw bytes read from the sensor every 2 seconds; using the adafruit-circuitpython-bme280 library, you directly get temperature in °C, humidity in %, and pressure in hPa.

Common Errors

• I2C not enabled: i2cdetect -l lists no buses; enable it via raspi-config and then reboot.
• Wrong bus number: on Raspberry Pi OS, the user bus is 1 (/dev/i2c-1), not 0.
• Address 0x77 instead of 0x76: check the marking on the module or test both addresses with i2cdetect.
• Powering an unregulated module with 5 V: most BME280 modules accept 3.3-5 V, but the I2C logic level must remain at 3.3 V.
• SDA/SCL swapped: no response; swap the two wires and run i2cdetect again.