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.

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.

feklee / MultiTrans