RS485 Hardware Network 2 – Multi-Byte Communication

Edit: I don’t really make a point of saying it, but the common ground between the modules isn’t nesesarry.

Here’s a video of the software running on the boards.

So for this example,  there are 4 bytes being transmitted from the master to the slaves.

  1. Start of Transmission (0xDB)
  2. ID of the slave to talk to
  3. The type of command
  4. The data that is transmitted

A transmission to set the pwm value of the green led on the slave with the ID 1 to 100 would be:

This is the schematic of the circuit for this example:

This is the code running on the master Arduino:

This is the code running on the slave Arduinos:

5 Comments

  1. Hi,

    I notice that you have a common ground between all three RS485 modules. My understanding is that RS485 is a balanced (longish range) two wire link, is that correct or have I confused it with RS232. I ask because I have a project in mind which uses some commercial RS485 modules and an arduino.

    Regards Alan

    1. Hi Alan,
      You’re correct, the common ground isn’t necessary. You are also not the first person to point out this error, I’ll make a post updating the schematic soon.
      Best,
      Devon

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