Introduction

MultiTrans is a multi channel transceiver, for AVR based Arduinos connected by wire or via IR.

Features

• Transceiver: Transmit and receive simultaneously via a single pin. (No clock line needed.)

• Multi channel: Multiple pins can transceive simultaneously.

• Collision detection: One pin can start sending without worrying if the other side is sending as well. Collisions are automatically detected and circumvented. No information is lost.

• Infrared option: Bi-directional communication through air, if needed. Further communication channels may be possible as well but have been untested.

• Maximum uni-directional data rates on an Arduino Uno / Pro Mini:

  • Communication with one peer: 12 kbit/s

  • Communication with four peers: 3 kbit/s

  Bi-directional data rates are a little less than half of the above rates in each direction.

Limitations

• Buffers:

  • The buffer on the transmitting end can contain 256 bits at the most. For each character, 21 bits are necessary. This equates to 12 characters.

  • The buffer on the receiving end can only contain up to 255 pin change events.

  • Flushing the buffer on the receiving end takes some time.

  The system is thus best used for short bursts of data with sufficient idle time in between.

• No built-in error checking. You may want to implement your own error checking, to take care of:

  • If you have a flaky connection between the Arduinos, for example due to bad electrical contacts, then bits may get lost.

  • Theoretically, i.e. if timing is perfectly right, the collision detection built into MultiTrans may fail resulting in bit loss.

• It only works with AVR based Arduinos. In fact, code so far has only been tested with the Arduino Pro Mini and the Arduino Uno.

• Timers are occupied:

  • 8-bit Timer/Counter2 (TC2), for transmitting

  • 16-bit Timer/Counter1 (TC1), for receiving

Examples

• Simple: bi directional communication between two Arduinos

  

• Triangle: Arduinos communicating in a triangle

  

• Stress test (advanced): for testing maximum and minimum data rates with five Arduinos all communicating simultaneously

  

• IR: bi directional communication through air

  

Character encoding

Transmitted are individual characters. Timing diagram:

There is no additional protocol.

Coding conventions

Coding conventions are based on the Arduino Style Guide for Writing Libaries with additions:

• Class (not struct) member variables (not constants) are prefixed with an underscore.

• Identifiers of template parameters:

  • types: T, U, V, …

  • typed parameters: t, u, v, …

• Constants follow the same naming conventions as variables.

• Maximum line length: 80 characters

• Maximum identifier length: 32 characters

• To avoid naming conflicts with other Arduino libraries, #pragma once instead of include guards is used, except for the top level include file.

• Comments are written with Markdown syntax.

License

Except where noted otherwise, files are licensed under the WTFPL.

Copyright © 2018–19 Felix E. Klee

This work is free. You can redistribute it and/or modify it under the terms of the Do What The Fuck You Want To Public License, Version 2, as published by Sam Hocevar. See the COPYING file for more details.