i2C: home page

[last updated: 2025-05-12]
i2c on DigiSpark
i2c on rPi for GMC
SPI vs. i2c
i2c: minimum code
Programming Wire.h library commands:
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• i2C (Inter-Integrated Circuit) is a protocol for serial communication.
  It is usually used between components in an embedded system (which already share power and ground lines).
  In such a system, it only requires 2 signal lines
      (if it is not being used in an "embedded" system, then at least the ground lines must be connected between master and slave):
  • SCL = serial Clock (usu pin A5)
  • SDA = serial Data (usu pin A4)
  • SDA & SCL lines need pullup resistors,
    however the Wire.h library enables the Arduino's internal pullups
    when initializing with Wire.begin().
• Two or more nodes communicate according to:
  • one master
    (however there are ways to use more than one master - see details later)
  • one or more slaves
• Range is probably 1 - 3 meters.
  • researching this subject on the net reveals lots of different opinions:
  • The answer apparently depends mostly on capacitance between the wires.
  • There are reports of achieving 25m or even more.
  • At some point I'll just get some longer wires and test it myself...
• Most common library is built-in Wire.h
• Programming Wire:

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