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<title>Raspberry Pi camera/LED demo</title>
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</head>
<body class="article">
<div id="header">
<h1>Raspberry Pi camera/LED demo</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_overview">Overview</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The <a href="/">demo</a> consists of web app providing access to a webcam and a LED attached to a RaspberryPi.
The device is assumed to have a limited bandwidth towards the server hosting the web app.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_objective">Objective</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The demo shows how to use websockets to communicate bidirectionally with an embedded device using standard protocols.</p>
</div>
<div class="paragraph">
<p>It also shows that it&#8217;s possible to use Smart.c to develop also the cloud endpoint and expose WebSocket and RESTful APIs
easy to integreate with modern web stacks.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_how_it_works">How it works</h2>
<div class="sectionbody">
<div class="imageblock">
<div class="content">
<img src="docs/arch.png" alt="arch">
</div>
</div>
<div class="paragraph">
<p>There are two components, once with runs on the device (<code>device_side</code>) and one that runs on a stronger machine
and with more bandwidth (<code>cloud_side</code>).</p>
</div>
<div class="paragraph">
<p>The device app connects to the cloud app via websocket and sends a new jpeg frame as fast as the underlying <code>raspistill</code> camera
grabbing application can handle. The device automatically attempts reconnecting.</p>
</div>
<div class="paragraph">
<p>The cloud side serves the webapp static pages and serves an MPJEG image on <code>/mpjg</code>.
The MPJEG image handler blocks all the clients until a JPEG frame arrives via websocket
Sergey Lyubka's avatar
Sergey Lyubka committed
457
and then every client will receive a copy of the frame.</p>
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</div>
<div class="paragraph">
<p>The web app can turn on and off the LED via a RESTful api accessible via the <code>/api</code> handler.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_installation">Installation</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_server_side">Server side</h3>
<div class="listingblock">
<div class="content">
<pre>git clone https://github.com/cesanta/mongoose
cd mongoose/examples/web_demo
make cloud_side &amp;&amp; ./cloud_side 0.0.0.0:8080</pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_raspberry_pi">Raspberry Pi</h3>
<div class="paragraph">
<p>The instructions provided here are tailored for the Raspbian distribution.</p>
</div>
<div class="sect3">
<h4 id="_dependencies">Dependencies</h4>
<div class="dlist">
<dl>
<dt class="hdlist1">jpegoptim</dt>
<dd>
<p>apt-get install jpegoptim</p>
</dd>
<dt class="hdlist1">camera</dt>
<dd>
<p>run raspi-config and enable camera</p>
</dd>
</dl>
</div>
</div>
<div class="sect3">
<h4 id="_led">LED</h4>
<div class="paragraph">
<p>In order to access the led on your <a href="http://www.qdh.org.uk/wordpress/?page_id=15">HotPi</a>
board you need to export the gpio pins:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>for i in 22 23 24; do
  echo $i &gt;/sys/class/gpio/export
  echo out &gt;/sys/class/gpio/gpio$i/direction
  chgrp pi /sys/class/gpio/gpio$i/value
done</pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="_build_and_run">Build and run</h4>
<div class="listingblock">
<div class="content">
<pre>git clone https://github.com/cesanta/mongoose
cd mongoose/examples/web_demo
make device_side &amp;&amp; ./device_side yourserver:8080</pre>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<div id="footer">
<div id="footer-text">
Last updated 2014-11-03 21:30:06 GMT
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