i2c-devices is a library for using I2C devices.


Usage of I2CDevice class directly:

require "i2c"
require "i2c/driver/i2c-dev"
device = 0x60, driver:"/dev/i2c-1"))

# like i2c-tools's i2cget command
length = 3
device.i2cget(0x01, length)

# like i2c-tools's i2cset command
device.i2cset(0x01, 0x11, 0x12 ... )

or pre-defiend device driver class:

require "i2c/device/acm1602ni"

lcd =

lcd.put_line(0, "0123456789ABCDEF")

with driver class

require "i2c/device/mpl115a2"
require "i2c/driver/i2c-dev"

mpl ="/dev/i2c-0"))
p mpl.calculate_hPa

or GPIO backend driver (this is very slow)

require "i2c/device/mpl115a2"
require "i2c/driver/gpio"

mpl =
    sda: 23, # pin 16 in raspberry pi
    scl: 24, # pin 18 in raspberry pi

p mpl.calculate_hPa



Generic class for manipulating I2C device. address, driver: driver)

  • address : Integer : 7-bit slave address without r/w bit. MSB is always 0.
  • driver : I2CDevice::Driver : backend driver class. (default: I2CDevice::Driver::I2CDev)

I2CDevice#i2cset(*data) #=> Integer

Write data to slave.

Returns Integer which is bytes length wrote.

I2CDevice#i2cget(param, length=1) #=> String

This method read data from slave with following process:

  1. Write param to slave
  2. re-start
  3. Read data until NACK or length

Returns String.


This depends on /dev/i2c-* (i2c-dev) feature on Linux. You may load i2c-dev kernel module.

  • path : String : Path to /dev/i2c-*


This depends on /sys/class/gpio feature on Linux and implements by bit-banging. sda, scl: scl, speed: speed)

  • sda : Integer : Pin number of SDA.
  • scl : Integer : Pin number of SCL.
  • speed : Integer : I2C clock speed in kHz. (default: 1)

Pin number of sda and scl is not real pin number but logical pin number. Eg. In Raspberry Pi, specifing sda: 23, scl: 24 means using 16 and 18 pin.

You can specify 100 kHz or 400 kHz (or more) to speed but speed is rate-limited by host CPU speed. Typically, this module fall short of requirements of I2C spec (in Raspberry Pi, clock speed is about 1.3kHz). But most slave devices support DC~100kHz clock speed.


Currently this library depends on Linux's i2c-dev or sysfs with GPIO feature.

  • I2CDevice::Driver::I2CDev /dev/i2c-0 (i2c-dev), default
  • I2CDevice::Driver::GPIO /sys/class/gpio (GPIO)


  • More supported devices