Monday, January 6, 2014

Arduino Yun - Introduction + Controlling GPIO via a web server

My Arduino Yun arrived over the weekend and I was surprised by how small it was compared to my Pi or Galileo. It is roughly the size of a credit card (see below).



Some of the things I really like about this:

  • Built in Wifi, micro SD card reader and  Linux OS (Linino)
  • Small form factor - ideal for applications that I am interested in like robotics and home automation
  • Easy Wifi setup in any new location
  • Ability to program sketches over Wifi and use the console terminal wirelessly to see events happening in the sketches.

This is a great guide to get started: http://arduino.cc/en/Guide/ArduinoYun. I used it to setup WiFi and allow open REST API access.

My first goal was to set up a USB webcam and install motion on my Yun. I achieved this by using the package management to install the necessary driver and packages
opkg install kmod-video-uvc motion

I plugged in my webcam via a USB hub and I was happy to see that it showed up after using dmesg and lsusb.

I started up motion and was able to see that it streams to a Firefox browser seamlessly. Goal #1 accomplished.

Next, I wanted to use a web browser to control GPIO to enable my next project which is a web controlled robot. So I wrote a simple sketch that uses browser buttons to turn the on board LED on and off. The sketch can be downloaded  here.

To get this to work I had to do one step that was not clearly documented anywhere. I had to manually create a soft link in my /www/ folder for sd:
ln -s /mnt/sda1 /www/sd

Another key thing to note here, is that your sketch folder needs to have a www sub folder with the index.html and zepto.min.js file in it. When your sketch is uploaded via WiFi, the contents of the www folder and automatically copied to /www/sd/<sketchname> folder

The REST calls to /arduino are made from the index.html file. To undestand what the REST API is, I would encourage you to read up on it in the getting started URL mentioned above.

If you view the source of the html, you will see this:


<script type="text/javascript">

    function ledon()
   {
       $('#content').load('/arduino/ledon');
   }
   function ledoff()
  {
      $('#content').load('/arduino/ledoff');
  }

</script>


It basically passes the ledon/ledoff commands to the Arduino once the buttons are pressed. The sketch simply looks for this and manipulates the GPIO:


if (command == "ledon") {
       digitalWrite(13, HIGH);
 }

else if (command == "ledoff") {
       digitalWrite(13, LOW);
}

After you have uploaded the sketch over to your Yun, you can use any browser to go to http://your_yun_name.local/sd/webled

You should see these buttons which will allow you to control the on board LED.


Hope this helps others who are trying to attempt something similar.

6 comments:

  1. Thanks man, that's exactly what I was looking for!

    toni

    ReplyDelete
    Replies
    1. Glad to hear that it helped you. Good luck!

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    2. This comment has been removed by the author.

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    3. Thanks very much for this blog post. It's very clear.
      It isn't necessary to create a soft link if you put the folder "www" in "/mnt/sda1/arduino". In this case, the link to www/sd is automatically created. (http://forum.snootlab.com/viewtopic.php?t=519&p=4788)

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    4. Thanks for this tutorial, excelent.
      Yes, its true, www/sd is automatically created.
      I dont need create the "www" in "/mnt/sda1/arduino".

      Regards

      Delete
  2. Many many thanks for the nice tutorial and the very clear explanations.
    I hope to see more from you on Arduino Yún.

    ReplyDelete