The __Inter-integrated Circuit  (I²C) Protocol__ (pronounced ''I-squared-C'') is a hardware serial interface (or "protocol") intended to allow multiple "slave" components to communicate with one or more "master" components. It used across many microprocessors and microcontrollers, including the [Raspberry Pi]. 

I²C permits sensors and other IO devices to be connected to the controller (and/or each other) with only four wires (or really only ''two'' if you don't count Vcc and ground): 

# __3-6V__ (Vcc)
# __SDA__ (Serial Data Line)
# __SCL__ (Serial Clock Line)
# __GND__ (Ground)

The Pimoroni "Breakout Garden" set of I²C sensors also includes an "__{{{INT}}}__" (interrupt) pin, ''AKA'' "{{{GCLK}}}" or "{{{GPIO4}}}".

!! To View the Current I²C Devices

To see what's connected on your Raspberry Pi, type (not including the {{{%}}} prompt):
{{{
   % i2cdetect -y 1
}}}
and you'll see something like:
{{{
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- 14 15 -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- 28 -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- 74 75 -- 77  
}}}


!! Known I²C Devices

Some well known I²C products. No two I²C may share the same address on an I²C bus, otherwise there will be contention.

|| Stock || Brand  || Description                               || 7 bit address         || Notes
| 1 | Pimoroni     | [RGB Potentiometer|https://shop.pimoroni.com/products/rgb-potentiometer-breakout] | 0x0E ‡                 | uses [Nuvoton MS51|NuvotonMS51]
| 1 | Pimoroni     | [RGB Encoder|https://shop.pimoroni.com/products/rgb-encoder-breakout] | 0x0F ‡                 | uses [Nuvoton MS51|NuvotonMS51]
| 1 | Pimoroni     | [IO Expander|https://shop.pimoroni.com/products/io-expander] | 0x18 ‡ | uses [Nuvoton MS51|NuvotonMS51]
| 2 | Pimoroni     | [LSM303D 6DoF Motion Sensor|https://shop.pimoroni.com/products/lsm303d-6dof-motion-sensor-breakout] | 0x1D / 0x1E †          |
| 1 | Pimoroni     | [LTR-559 Light & Proximity|https://shop.pimoroni.com/products/ltr-559-light-proximity-sensor-breakout] | 0x23                   |
| 3 | Pimoroni     | [VL53L1X Time of Flight|https://shop.pimoroni.com/products/vl53l1x-breakout] | 0x29               | range 40mm-4m
| 1 | Adafruit     | VL6180X Time of Flight Distance Sensor     | 0x29                   | range 5-100mm
| 2 | Adafruit     | [HT0740 10A Switch|https://shop.pimoroni.com/products/ht0740-breakout] | 0x38 / 0x39 † |
| 1 | Adafruit     | INA260 Current Sensor                      | 0x40 †                 |
| 2 | Pimoroni     | [11x7 LED Matrix|https://shop.pimoroni.com/products/11x7-led-matrix-breakout] | 0x75 / 0x77 †          | 77 will be in conflict with 5x5
| 4 | Pimoroni     | [5x5 RGB Matrix|https://shop.pimoroni.com/products/5x5-rgb-matrix-breakout] | 0x74 / 0x77 †       | 77 will be in conflict with 11x7
| 2 | Pimoroni     | [ADS1015 +/-24V ADC 3 Channel|Ads1015AnalogDigitalConverter] | 0x48 / 0x49 † |
| 2 | Adafruit     | ADS1015 12 bit ADC 4 Channel w Prog Gain   | 0x48 - 0x4B †          |
| 2 | PiBorg       | Thunderborg                                | 0x10 / 0x11 †          |
| 1 | PiBorg       | Ultraborg                                  | 0x36                   |
| 1 | Pimoroni     | [ICM20948 9-DOF Motion Sensor|https://shop.pimoroni.com/products/icm20948] | 0x68 / 0x69 † |
| 1 | Adafruit     | [BNO055 IMU Sensor|BNO055ImuSensor]        | 0x28 / 0x29            |
| 0 | Adafruit     | VCNL4010 Proximity Sensor                  | 0x13                   |
| 0 | Adafruit     | LSM9DS1 Accel Gyro Mag Temp 9-DOF          | 0x1C / 0x1E Accel, 0x6A / 0x6B for Gyro |
| 0 | Adafruit     | VL53L0X Time of Flight Distance Sensor     | 0x29                   | range 50-1200mm (2m on long range)
| 1 | Pimoroni     | [AS7262 6-channel Spectral Sensor (Spectrometer)|https://shop.pimoroni.com/products/as7262-6-channel-spectral-sensor-spectrometer-breakout] | 0x49              | 6 spectral channels (450, 500, 550, 570, 600, 650nm)


† jumper selectable
‡ software configurable

"Stock" is how many [Murray] has in his robot laboratory as part of exploratory design and development of the [KR01] robot.

!! Links

* [I2C|https://en.wikipedia.org/wiki/I%C2%B2C] on Wikipedia
* [Configuring I2C|https://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup/configuring-i2c] from AdaFruit 
* [I2C|https://learn.sparkfun.com/tutorials/i2c] on SparkFun
* [Adafruit's I2C Address List|https://learn.adafruit.com/i2c-addresses/the-list]
* [Raspberry Pi SPI and I2C Tutorial|https://learn.sparkfun.com/tutorials/raspberry-pi-spi-and-i2c-tutorial/all]
* [Pi clock-stretching bug|https://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html]
* [Adventures in I2C: clock stretching on the Raspberry Pi|https://www.recantha.co.uk/blog/?p=19880], A good article about the Pi and I2C
* [Raspberry Pi slave library for Arduino|https://github.com/pololu/pololu-rpi-slave-arduino-library], Pololu's library for Pi to Arduino comms via I2c

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[{Tag Hardware}]