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Some comments on Arduino Dock and I2C communication

  • The only method to communicate between the Omega and the Arduino Dock is via I2C

    In https://wiki.onion.io/Tutorials/Arduino-Dock/Using-the-Arduino-Dock it says:

    • Using I2C in a Sketch

      Right now the Onion Library joins the I2C bus with an address of 0x08 and listens for a write of 0xde 0xad (get it? 'dead' ha ha ha) when resetting. If you need a Sketch to use I2C, make sure to build this functionality into your I2C handling to comply with the Arduino Dock flashing procedure.

    This has a few implications:

    1. Since the Arduino can only join the I2C bus as a master (using Wire.begin()) or a slave (using Wire.begin(<i2c-addr>)) the above statement REQUIRES the Arduino to join the I2C bus as a slave using Wire.begin(0x08)

    2. Since it is required from the above that the Arduino lists for a write from the Omega of 0xde 0xad it is necessary to know what action the Arduino should take when it receives this message.

      From gleaning the code in https://github.com/OnionIoT/Onion-Arduino-Library/blob/master/Onion/OnionLibrary.cpp it is found that the code to be executed on the Arduino on receipt of this message is:


      It would be extremely helpful if this was described in the documentation.

    3. Because the Arduino HAS TO BE an I2C slave on address 0x08 as above, it is not possible for it to be an I2C master and control other I2C devices.

      This is not necessarily a big deal since the Omega can still use I2C to access any Arduino I2C shields that may be plugged into the Arduino Dock

      But again, it would be helpful if this was clear in the documentation

    4. Note that sending the 0xde 0xad message from the Omega to the Arduino can be performed by the following call to the code in https://github.com/OnionIoT/i2c-exp-driver/blob/master/src/lib/onion-i2c.c in the https://github.com/OnionIoT/i2c-exp-driver library:
      i2c_write(0, 0x08, 0xde, 0xad);

  • I am still relatively new to the Arduino world - I am guessing that if I have an Arduino sketch that is collecting data from I2C sensors such as BME280 or Gas sensors then the sketch won't work in with the Arduino dock R2 + Omega 2+? I would have re-write those sketches?

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