The __Inter-integrated Circuit  (I%%sup 2%%​C) 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     | LTR-559 Light & Proximity                  | 0x23                   |
| 1 | Pimoroni     | VL53L1X Time of Flight (ToF)               | 0x29                   | range 40mm-4m
| 1 | Adafruit     | VL6180X Time of Flight Distance Sensor     | 0x29                   | range 5-100mm
| 1 | Pimoroni     | 11x7 LED Matrix #1                         | 0x75                   |
| 1 | Pimoroni     | 11x7 LED Matrix #2                         | 0x77                   |
| 1 | Pimoroni     | 5x5 RGB Matrix                             | 0x74 / 0x77            | 77 will be in conflict with 11x7 #2
| 1 | Pimoroni     | [ADS1015 +/-24V ADC 3 Channel|Ads1015AnalogDigitalConverter] | 0x48 / 0x49     |
| 2 | Adafruit     | ADS1015 12 bit ADC 4 Channel w Prog Gain   | 0x48 - 0x4B (jumpers)  |
| 1 | PiBorg       | Thunderborg                                | 0x10 / 0x11            |
| 1 | PiBorg       | Ultraborg                                  | 0x36                   |
| 1 | Pimoroni     | ICM20948 9-DOF Motion Sensor               | 0x68 / 0x69            |
| 1 | Adafruit     | BNO055 Absolute Orientation Sensor         | 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)

"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
* [Raspberry Pi SPI and I2C Tutorial|https://learn.sparkfun.com/tutorials/raspberry-pi-spi-and-i2c-tutorial/all]


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[{Tag Hardware}]