🛠 Capteur I2C : température et pression avec BME280

Objectives

Enable the I2C bus on the Raspberry Pi 3 A+, detect a BME280 sensor (temperature/humidity/pressure), and read it using Python. The 40-pin connector exposes I2C0: SDA = GPIO2 (pin 3), SCL = GPIO3 (pin 5), 3.3 V power supply — 3.3 V logic only, no onboard ADC.

Hardware

• Raspberry Pi 3 A+ running Raspberry Pi OS Bookworm
• BME280 module (I2C, address 0x76 or 0x77 depending on the ADDR pin configuration)
• 4 Dupont wires: SDA→pin 3, SCL→pin 5, VCC→3.3 V (pin 17), GND→pin 25
• >

Complete Code

# 1) Activer I2C : sudo raspi-config -> Interface Interfacing Options -> I2C
#    ou sans menu :
sudo sed -i 's/^#*dtparam=i2c_arm=on/dtparam=i2c_arm=on/' /boot/firmware/config.txt
sudo apt install -y i2c-tools python3-smbus
sudo reboot
i2cdetect -y 1        # le capteur doit répondre (0x76 ou 0x77)

#!/usr/bin/env python3
# lire_bme280.py — lecture brute des registres (adresse 0x76)
import smbus, time

BUS, ADDR = smbus.SMBus(1), 0x76

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

# configuration capteur (oversampling x2, mode forcé)
BUS.write_byte_data(ADDR, 0xF2, 0x01)          # ctrl_hum
BUS.write_byte_data(ADDR, 0xF4, 0x27)          # ctrl_meas
BUS.write_byte_data(ADDR, 0xF8, 0x00)          # config
while BUS.read_byte_data(ADDR, 0xF3) & 0x08:   # busying ?
    time.sleep(0.01)

t = read_regs(0xFA, 3)
temp = ((t[0] << 16 | t[1] << 8 | t[2]) >> 4) / 100.0
print(f"Temperature : {temp:.2f} C")

Expected Verification

i2cdetect -y 1 displays an address (0x76 or 0x77) in the grid; the script displays a temperature consistent with the room (20–30 °C). In a thermal chamber, the value follows the setpoint.

Common Errors

• I2C not enabled: i2cdetect -l lists nothing → enable dtparam=i2c_arm=on and reboot.
• Sensor at 0x77 while the script assumes 0x76: check the module's ADDR pin.
• SDA/SCL swapped: i2cdetect finds nothing and the bus remains stuck.
• Stay at 3.3 V on both the power supply and logic sides on the 3 A+.