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I2C bus

The pins and clock of one I2C bus, set once and shared by every node on it. A display and a sensor can sit on the same bus, each at its own address.

Each I2C node has an I2C bus field. Pick a bus, or add one with +. A new bus takes the lowest bus number not yet used in the flow.

Settings

  • bus — the chip's I2C peripheral number. Default 0. Each bus number is used once per flow.
  • scl pin / sda pin — the GPIO pins. Required, and different from each other.
  • frequency (Hz) — the clock. Default 100000, which suits most sensors. Displays that can take it run at 400000.

Behavior

Changing a bus changes it for every node on it. The bus's two pins are claimed like any other pin, so no other node can use them (see Hardware is shared).

runtime.shared('i2c', 0) in a function node returns the flow's bus 0, already set up, to talk to a device that has no node of its own. It raises KeyError if no node in the flow uses that bus.

Errors

These stop the deploy:

  • No SCL or SDA pin: I2C bus 0 has no SCL pin set.
  • The same pin for both: I2C bus 0 uses pin 5 for both SCL and SDA.
  • Two bus settings with the same number, both in use: Two I2C bus settings both say bus 0.
  • A pin or bus number the board can't use for I2C. See What gets checked.