i2cscan

Lightweight I2C bus scanner for embedded Linux. Detects all devices on the bus and identifies known chips by reading their ID registers.

Works on any Linux system with I2C support — Armbian, OpenWrt, Debian, Buildroot, Yocto — from a single statically linked binary. No runtime dependencies.

Features

• Scans one or all I2C buses
• Detects devices using the same SMBus probing strategy as i2cdetect
• Identifies known chips by reading hardware ID registers (BME280, BMP280, MPU6050, LIS3DH, etc.)
• Falls back to address-based identification for devices without readable chip IDs (DS3231, SSD1306, EEPROM, etc.)
• Per-bus timeout protection — a hung bus won't block the entire scan
• Single static binary, no dependencies on i2c-tools

Building

Native (on the target board)

gcc -static -O2 -o i2cscan src/i2cscan.c

Cross-compile for aarch64

aarch64-linux-gnu-gcc -static -O2 -o i2cscan src/i2cscan.c

Requires kernel headers with linux/i2c-dev.h and linux/i2c.h at build time. At runtime, only /dev/i2c-* device nodes are needed.

Prerequisites

The I2C device nodes must exist on the target system.

Armbian / Debian:

sudo apt install i2c-tools
sudo modprobe i2c-dev

OpenWrt:

apk add kmod-i2c-core kmod-i2c-dev

Verify with ls /dev/i2c-*.

Usage

i2cscan --bus <n>       # scan a specific bus
i2cscan --bus-all       # scan all available buses
i2cscan --help          # show help

Example output

I2C scan
========

/dev/i2c-1:
  0x50  EEPROM (24Cxx)
  0x68  DS3231 (RTC) / MPU6050 / PCF8523
  0x76  BME280

/dev/i2c-3:
  (no devices found)

How it works

Detection uses SMBus ioctls, matching the behavior of i2cdetect -y:

Address range	Probe method	Why
0x30–0x37	SMBus quick write	Safe for devices that interpret reads as commands
0x50–0x5F	SMBus quick write	Safe for EEPROMs (avoids accidental reads)
All others	SMBus read byte	General-purpose detection

After a device is found, i2cscan tries to read known chip ID registers (e.g. 0xD0 for Bosch sensors, 0x75 for InvenSense IMUs, 0x0F for ST sensors). If no register match is found, it falls back to a table of well-known fixed addresses.

Supported chips

Identified by register

Chip	Register	ID	Typical address
BME280	0xD0	0x60	0x76 / 0x77
BMP280	0xD0	0x58	0x76 / 0x77
BMP180	0xD0	0x55	0x77
BME680	0xD0	0x61	0x76 / 0x77
MPU6050	0x75	0x68	0x68 / 0x69
MPU6500	0x75	0x70	0x68 / 0x69
MPU9250	0x75	0x71	0x68 / 0x69
ICM-20689	0x75	0x98	0x68 / 0x69
LIS3DH	0x0F	0x33	0x18 / 0x19
LSM6DS3	0x0F	0x6A	0x6A / 0x6B
LSM6DSO	0x0F	0x69	0x6A / 0x6B
LIS3MDL	0x0F	0xBB	0x1C / 0x1E
HMC5883L	0x0A	0x48	0x1E

Identified by address

Address	Likely device
0x23	BH1750 (light sensor, ADDR=LOW)
0x27	PCF8574 (LCD/GPIO expander)
0x38	AHT20 (temperature/humidity)
0x3C–0x3D	SSD1306 (OLED display)
0x44–0x45	SHT3x (temperature/humidity)
0x48–0x4B	ADS1115 / TMP102 / PCF8591
0x50	24Cxx EEPROM
0x51	PCF8563 (RTC) / EEPROM
0x5C	BH1750 (light sensor, ADDR=HIGH)
0x68	DS1307 / DS3231 (RTC) / MPU6050 / PCF8523
0x76–0x77	BME280 / BMP280 / MS5611

Adding new chips

Edit the tables in i2cscan.c:

• known_chips[] — for devices with a readable ID register (preferred)
• known_addrs[] — for fixed-address devices without ID registers

License

MIT