🛠 Lire un capteur sur le bus I2C

Objectives

Enable the I2C bus of the BCM2835, detect a sensor (example: BME280 temperature/pressure/humidity) on I2C0 of the P1 connector, and read a measurement from Python using smbus.

Hardware

• Raspberry Pi Model B Rev 2, Raspbian legacy 32-bit
• I2C sensor 3.3 V (BME280 or equivalent), pull-up resistors if the module does not have them
• SDA on GPIO0 (P1-3), SCL on GPIO1 (P1-5), 3.3 V and GND. I2C0 is indeed on GPIO0/1 on this board; no reliable default address without i2cdetect.
• sudo apt install i2c-tools python-smbus

Complete code

# 1) Activer I2C: dans /boot/config.txt ajouter la ligne puis redemarrer
sudo nano /boot/config.txt
#   dtparam=i2c_arm=on
sudo reboot
# 2) Scanner le bus (adresse attendue: 76 ou 77 pour un BME280)
sudo i2cdetect -y 1

#!/usr/bin/env python
# lire_temp.py - lecture brute d'un registre via smbus
import smbus

bus = smbus.SMBus(1)                 # i2c-1 (le seul expose sur P1)
ADDR = 0x76                          # adresse trouvee a l'etape i2cdetect
try:
    who = bus.read_byte_data(ADDR, 0xD0)
    print("chip id: 0x%02x" % who)   # 0x60 pour un BME280
except IOError:
    print("Pas de reponse sur l'adresse %02x" % ADDR)

Expected verification

i2cdetect -y 1 displays the sensor address in the grid; the Python script prints the chip ID (0x60 for a BME280). No XX should remain everywhere in the grid.

Common errors

• dtparam=i2c_arm=on forgotten or reboot omitted: i2cdetect responds "Could not open file /dev/i2c-1".
• SDA/SCL swapped: nothing appears in the scan, the sensor does not "respond".
• 5 V sensor powered at 3.3 V (or vice versa on the lines): check the logic level, the board is 3.3 V.
• Wrong address (0x76 vs 0x77 depending on the SDO pin): scan before coding.