🛠 Premier capteur sur le bus I2C

Objectives

Enable the I2C bus, scan the bus with i2cdetect, then read an environmental sensor from Python using smbus2. The BCM2711 exposes up to 6 I2C controllers; i2c-1 (pins 3 and 5) is the standard user bus.

Hardware

• Raspberry Pi 4B + BME680 (or BME280) sensor on a breakout board
• 4.7 kOhm pull-up resistors if the breakout board does not have them
• sudo apt install i2c-tools python3-smbus2

Complete code

# Activer I2C : sudo raspi-config -> Interface Options -> I2C (ou dtoverlay=i2c-rtc en plus)
sudo i2cdetect -y 1        # balayage du bus i2c-1

#!/usr/bin/env python3
# lecture_i2c.py - lire l'identifiant de puce du BME680
import smbus2

ADDR = 0x76               # 0x76 ou 0x77 selon la broche SDO du module
# 
bus = smbus2.SMBus(1)
chip_id = bus.read_byte_data(ADDR, 0xD0)
print(f"Chip ID 0x{chip_id:02X} (BME680 attendu : 0x61)")

Expected verification

i2cdetect -y 1 displays a table; one cell (often 76 or 77) appears: this is the sensor. The script displays Chip ID 0x61 for an authentic BME680. No cell appears: the bus is inactive, SDA/SCL wiring is reversed, or the module is not powered.

Common errors

• Forgetting to enable I2C in raspi-config and then rebooting: i2cdetect responds with Could not open bus.
• Reversing SDA (pin 3) and SCL (pin 5): nothing appears in the scan.
• Powering the sensor with 5 V on a bus expected to be 3.3 V: check the breakout board documentation.
• Wrong address (0x76 vs 0x77): the i2cdetect scan provides the correct one.
• No pull-up resistors on long cables: lines do not rise, resulting in random readings.