Arduino Yun Serial to WebSocket Bridge

This code is based largely on the following post: http://niltoid.com/blog/raspberry-pi-arduino-tornado/. The following topics in the Arduino forum were also helpful:

• WebSockes with Yun?
• Tty for serial port to Arduino from Linino

This bridge was designed to use BreakoutJS with an Arduino Yun without the use of Breakout Server (since the server is running directly on the Yun). This code could easily be adapted for your own purposes.

This bridge will work for applications the require sending and receiving binary data. The bridge receives a stream of bytes from the arduino and broadcasts a string of comma separated values to all listenting web clients (in your client app, simply split the received string on the comma). On the inverse it receives a string of comma separated values (an array of unsigned bytes sent as a string) from each web client and sends a string of chars (non delimited) to the arduino.

This is experimental code. Try it at your own risk. If you have ideas for improvement, please start a discussion or open a pull request.

In order to use this bridge you'll first need to install a few things on your Yun:

1. ssh into your Yun:

   On a mac:

   $ ssh [email protected]

   Enter your password when prompted

2. Install dependencies:

   You'll need to install pyserial, pyopenssl, python-openssl. Enter the following 3 commands.

   $ opkg update
   $ opkg install python pyserial
   $ opkg install pyopenssl
   $ opkg install python-openssl

3. Install Tornado WebServer (this is used as the WebSocket server):

   Download the Tornado using curl and follow the commands below to build:

   $ curl -o /tmp/tornado 'https://pypi.python.org/packages/source/t/tornado/tornado-3.1.1.tar.gz' -k
   $ cd /tmp/
   $ tar xvzf tornado
   $ cd tornado-3.1.1
   $ python setup.py build
   $ python setup.py install

   I'm currently only using the server for WebSockets, but you can optionally host static web pages from the server as well. I have commented out that functionality. See comments in the code to enable.

4. Copy the contents of linino/breakout/ to your Yun.

   This will copy the breakout directory to the home directory in your Yun's Linino linux installation. You can change the destination to copy them elsewhere. Google "scp" if you're not familiar with the use of secure copy.

   $ scp -r ./breakout [email protected]:~/

   Enter your password when prompted

5. Compile and upload arduino/StandardFirmataYun

6. Disable Arduino bridge serial communication:

   Because this code essentialy hijacks Serial1 (which is what the Arduino Bridge library uses to communicate with linino) you'll need to prevent the linino bridge from accessing Serial1. The following steps will get that set up (but heed the warning!!!).

   Note that performing the following step is necessary to get Firmata to work with WebSockets on the Yun. However if you do this, you will not be able to use the Arduino Bridge library until you undo this change.

   It may be wise to make a backup before modifying this file. Do not ever delete the inittab file or you may brick your Yun.

   $ cd /etc/
   $ vim inittab

   In the inittab file, comment out the line beginning with ttyATH0:

   ...
   # ttyATH0::askfirst:/bin/ash --login
   

   $ reboot -f

   At this point you'll need to close your session and log back in via ssh after a couple of minutes. If you have trouple ssh'ing into your Yun after this, see the troubleshooting section below.

7. Run the script

   $ cd ~/breakout   # or whever you copied the files to
   $ python server.py

   In the near future this will launch automatically when your Yun boots, but I'm keeping it this way for now while it's alpha.

8. Open one of files in examples\getting_started\ in a text editor.

   You'll need to updeate the hostname (1st parameter passed to IOBoard constructor) to the name or IP address of your Yun.

   Serve the file from a local webserver. You should be able to interact with your Yun. Note that at this time only a single client can reliably connect to a single Yun. If you uncomment line 29 of breakout/server.py you can establish a 2 client websocket connections to a single Yun. However any more than 2 greatly diminishes performance. I'm looking into the cause of this.

Troubleshooting

I've had difficulty establishing a ssh connection from time to time. If you absolutely cannot connect again after editing inittab, try this:

1. Load an example sketch that doesn't use Serial such as: Examples -> Basics -> BareMinimum
2. Power cycle the Yun and wait a couple of minutes for a full boot
3. ssh into the Yun (should work now)
4. Reupload StandardFirmataYun to the board

I know this is super annoying but it's the only thing I've found that works (somewhat reliably) so far.