Bridging Arduino to AutobahnPython via Serial

This demo shows how to shuffle data between WAMP clients and a device connected via a serial port like Arduino to a machine hosting the WAMP server.

We use an Arduino device connected to a notebook, and a browser running somewhere.

Here are some videos - sorry, bad quality. But you should get the idea:

• http://www.youtube.com/watch?v=va7j86thW5M
• http://www.youtube.com/watch?v=aVJV2z-lQJE

Overview

Here is how stuff is connected:

  Arduino,
  other serial devices

     <= Serial over USB =>

  PC / Autobahn

     <= WebSocket/WAMP over Internet =>

  Browser (AutobahnJS),
  Python (AutobahnPython),
  Smartphone (AutobahnAndroid),
  ...

How it works

serial device => WebSocket/WAMP client

The Autobahn-based server will receive data from the device vi serial (over USB) and dispatch data received as WAMP PubSub events on topics upon which clients can subscribe.

WebSocket/WAMP client => serial device

The Autobahn-based server provides WAMP RPC endpoints which clients can call. The server will then forward the commands to the device via serial (over USB) to the device.

The protocol spoken on the serial wire is a very simple, small adhoc text based one.

The protocol spoken on the internet connection is WAMP http://wamp.ws over WebSocket.

We use WAMP running on top of standard WebSocket, since WAMP brings us simple RPC and PubSub .. higher level than raw WebSocket.

Discussion

Pros:

• Using serial means you can connect a lot of devices .. serial support is widespread.

Cons:

• You need to invent some small custom protocol for the comms on serial wire

• You must have a physical connection between the device and the PC/Autobahn server

For the reasons above, we plan to have a AutobahnAndroid implementation!

Thing is: there are (somewhat) emerging WebSocket implementations for Arduino already.

But what we want to have is full WAMP: http://wamp.ws

Now, to do it right, we want to use the binary message payload option that WebSocket brings, and not use JSON, but Bencode for payload format, since that is much more resource efficient, which matters on restricted devices (like Arduino). Therefor, we will first define a Bencode payload format binding for WAMP.

How to do it yourself

You will need AutobahnPython as server + PySerial for serial support in Python/Twisted.

Then, connect your serial device, run

python serial2ws.py

and open

http://localhost:8080/

in your browser.

Note: The serial2ws.py has a number of command line options for setting COM port, baudrate etc. Simply do a

python serial2ws.py --help

to get information on those.