I2C (Inter-Integrated Circuit)

A single pin GPIO has only two states, 0 and 1, which can be either driven by the computer associated with the GPIO pin, or driven by an external device connected to the pin. The timing of driving changes between the two states can be arbitary up to the resolution of the microcontroller that controls the GPIO.

As per the manual installation instruction for Install I2C library, you should install libi2c-dev and i2c-tools in order to interface with the I2C buses from linux, i.e.,

sudo apt-get install libi2c-dev i2c-tools

I2C via command line

The i2c-tools package provides the i2cdetect command line tool. This tool can be used to quickly detect and display the those devices on the bus that respond to the detect ping (1 is the I2C bus for this example):

sudo i2cdetect -y -r 1

Further information about the command line tool can be found from:

Important

As stated on the Ubuntu manual page for i2cdetect:
As there is no standard I2C detection command, i2cdetect uses arbitrary SMBus commands (namely SMBus quick write and SMBus receive byte) to probe for devices. By default, the command used is the one believed to be the safest for each address. See options -q and -r to change this behaviour.

I2C via C++

The most complete information and example for using the Linux user-space I2C functions is the I2C Driver for CPP provided as part of this repository.

The following may assist in if and when you develop you own custom use of the Linux user-space I2C functions:

I2C addresses

The following table lists the possible I2C address for the various sensor and actuator boards provided. The possible address are separated into three columns:

  • Default: the address of the component when hooked-up out-of-the-box.

  • Hardware Options: the possible addresses that can be configured by a hardware modification, usually by connecting or cutting pads on the breakout board.

  • Software Options: the possible addresses the can be configured through some form of software interface.

I2C Addresses per component

Component

Default Address

Hardware Options

Software Options

Pololu Simple Motor

Controller

0x0D (13)

None

Any 1

BMM150

Magnetometer

0x10 (16)

0x11 - 0x13

(17-19)

None

BMI088

Accelerometer

0x18 (24)

0x19 (25)

None

VL53L1X Laser

Distance Sensor

0x29 (41)

None

None

TCS34725 RGB

Colour Sensor

0x29 (41)

None

None

INA260 Current

Sensor

0x40 (64)

4 LBSs

0x41 - 0x4F

(64 - 79)

None

PCA9685 16-Channel

Servo Driver

0x40 (64)

6 LBSs

0x41 - 0x7F

(64 - 127)

None

PCA9685 All Call

I2C Bus Address

0x70 (112)

None

Any 2

BMI088

Gyroscope

0x68 (104)

0x69 (105)

None

ICM-20948 IMU

0x69 (105)

0x68 (104)

None

BMP390 Pressure

Sensor

0x77 (119)

0x76 (118)

None

1 Pololu provides a Windows based software that is used for setting the software defined I2C address.

2 This is a software defined address of the PCA9685 chip, however, it is enable on power-up with the default address indicated in the table. Hence the PCA9685 documentation provides the following remark: The default LED All Call I2C-bus address (70h or 0111 0000) must not be used as a regular I2C-bus slave address since this address is enabled at power-up