diff --git a/docs/images/composed_devices.dot b/docs/images/composed_devices.dot
index 5a1fe74..ad06867 100644
--- a/docs/images/composed_devices.dot
+++ b/docs/images/composed_devices.dot
@@ -21,4 +21,6 @@ digraph classes {
     Robot->Motor;
     Motor->DigitalOutputDevice;
     Motor->PWMOutputDevice;
+
+    Servo->PWMOutputDevice;
 }
diff --git a/docs/images/composed_devices.pdf b/docs/images/composed_devices.pdf
index d1178ac..387e179 100644
Binary files a/docs/images/composed_devices.pdf and b/docs/images/composed_devices.pdf differ
diff --git a/docs/images/composed_devices.png b/docs/images/composed_devices.png
index ad25571..692c1b1 100644
Binary files a/docs/images/composed_devices.png and b/docs/images/composed_devices.png differ
diff --git a/docs/images/composed_devices.svg b/docs/images/composed_devices.svg
index 1fd2dff..0afda6d 100644
--- a/docs/images/composed_devices.svg
+++ b/docs/images/composed_devices.svg
@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
-<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+<!-- Generated by graphviz version 2.36.0 (20140111.2315)
  -->
 <!-- Title: classes Pages: 1 -->
-<svg width="672pt" height="188pt"
- viewBox="0.00 0.00 672.00 188.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<svg width="708pt" height="188pt"
+ viewBox="0.00 0.00 708.00 188.00" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
 <g id="graph0" class="graph" transform="scale(1 1) rotate(0) translate(4 184)">
 <title>classes</title>
-<polygon fill="white" stroke="none" points="-4,4 -4,-184 668,-184 668,4 -4,4"/>
+<polygon fill="white" stroke="none" points="-4,4 -4,-184 704,-184 704,4 -4,4"/>
 <!-- RGBLED -->
 <g id="node1" class="node"><title>RGBLED</title>
-<polygon fill="#298029" stroke="#298029" points="56,-180 0,-180 0,-144 56,-144 56,-180"/>
+<polygon fill="#298029" stroke="#298029" points="55.5,-180 0.5,-180 0.5,-144 55.5,-144 55.5,-180"/>
 <text text-anchor="middle" x="28" y="-159.5" font-family="Sans" font-size="10.00" fill="#ffffff">RGBLED</text>
 </g>
 <!-- LED -->
@@ -26,13 +26,13 @@
 </g>
 <!-- PWMLED -->
 <g id="node3" class="node"><title>PWMLED</title>
-<polygon fill="#298029" stroke="#298029" points="172,-108 114,-108 114,-72 172,-72 172,-108"/>
+<polygon fill="#298029" stroke="#298029" points="171.5,-108 114.5,-108 114.5,-72 171.5,-72 171.5,-108"/>
 <text text-anchor="middle" x="143" y="-87.5" font-family="Sans" font-size="10.00" fill="#ffffff">PWMLED</text>
 </g>
 <!-- RGBLED&#45;&gt;PWMLED -->
 <g id="edge2" class="edge"><title>RGBLED&#45;&gt;PWMLED</title>
-<path fill="none" stroke="black" stroke-dasharray="5,2" d="M56.1322,-143.876C71.1684,-134.724 89.8671,-123.342 106.06,-113.485"/>
-<polygon fill="none" stroke="black" points="108.038,-116.379 114.76,-108.19 104.398,-110.4 108.038,-116.379"/>
+<path fill="none" stroke="black" stroke-dasharray="5,2" d="M55.5454,-144.233C70.6832,-135.019 89.664,-123.465 106.071,-113.479"/>
+<polygon fill="none" stroke="black" points="108.158,-116.305 114.88,-108.116 104.519,-110.326 108.158,-116.305"/>
 </g>
 <!-- LEDBoard -->
 <g id="node4" class="node"><title>LEDBoard</title>
@@ -51,7 +51,7 @@
 </g>
 <!-- LEDBarGraph -->
 <g id="node5" class="node"><title>LEDBarGraph</title>
-<polygon fill="#298029" stroke="#298029" points="237.5,-180 156.5,-180 156.5,-144 237.5,-144 237.5,-180"/>
+<polygon fill="#298029" stroke="#298029" points="237.25,-180 156.75,-180 156.75,-144 237.25,-144 237.25,-180"/>
 <text text-anchor="middle" x="197" y="-159.5" font-family="Sans" font-size="10.00" fill="#ffffff">LEDBarGraph</text>
 </g>
 <!-- LEDBarGraph&#45;&gt;LED -->
@@ -66,7 +66,7 @@
 </g>
 <!-- ButtonBoard -->
 <g id="node6" class="node"><title>ButtonBoard</title>
-<polygon fill="#298029" stroke="#298029" points="332.5,-180 255.5,-180 255.5,-144 332.5,-144 332.5,-180"/>
+<polygon fill="#298029" stroke="#298029" points="332.25,-180 255.75,-180 255.75,-144 332.25,-144 332.25,-180"/>
 <text text-anchor="middle" x="294" y="-159.5" font-family="Sans" font-size="10.00" fill="#ffffff">ButtonBoard</text>
 </g>
 <!-- Button -->
@@ -81,7 +81,7 @@
 </g>
 <!-- TrafficLightsBuzzer -->
 <g id="node8" class="node"><title>TrafficLightsBuzzer</title>
-<polygon fill="#298029" stroke="#298029" points="455.5,-180 350.5,-180 350.5,-144 455.5,-144 455.5,-180"/>
+<polygon fill="#298029" stroke="#298029" points="455.25,-180 350.75,-180 350.75,-144 455.25,-144 455.25,-180"/>
 <text text-anchor="middle" x="403" y="-159.5" font-family="Sans" font-size="10.00" fill="#ffffff">TrafficLightsBuzzer</text>
 </g>
 <!-- TrafficLightsBuzzer&#45;&gt;Button -->
@@ -126,23 +126,33 @@
 </g>
 <!-- DigitalOutputDevice -->
 <g id="node13" class="node"><title>DigitalOutputDevice</title>
-<polygon fill="#298029" stroke="#298029" points="542,-36 430,-36 430,-0 542,-0 542,-36"/>
-<text text-anchor="middle" x="486" y="-15.5" font-family="Sans" font-size="10.00" fill="#ffffff">DigitalOutputDevice</text>
+<polygon fill="#298029" stroke="#298029" points="577.5,-36 466.5,-36 466.5,-0 577.5,-0 577.5,-36"/>
+<text text-anchor="middle" x="522" y="-15.5" font-family="Sans" font-size="10.00" fill="#ffffff">DigitalOutputDevice</text>
 </g>
 <!-- Motor&#45;&gt;DigitalOutputDevice -->
 <g id="edge12" class="edge"><title>Motor&#45;&gt;DigitalOutputDevice</title>
-<path fill="none" stroke="black" stroke-dasharray="5,2" d="M533.427,-71.6966C525.798,-63.2198 516.477,-52.8636 508.124,-43.5826"/>
-<polygon fill="none" stroke="black" points="510.685,-41.1959 501.394,-36.1043 505.482,-45.8787 510.685,-41.1959"/>
+<path fill="none" stroke="black" stroke-dasharray="5,2" d="M542.326,-71.6966C539.285,-63.8132 535.617,-54.3042 532.239,-45.5464"/>
+<polygon fill="none" stroke="black" points="535.462,-44.1748 528.597,-36.1043 528.931,-46.6939 535.462,-44.1748"/>
 </g>
 <!-- PWMOutputDevice -->
 <g id="node14" class="node"><title>PWMOutputDevice</title>
-<polygon fill="#298029" stroke="#298029" points="664,-36 560,-36 560,-0 664,-0 664,-36"/>
-<text text-anchor="middle" x="612" y="-15.5" font-family="Sans" font-size="10.00" fill="#ffffff">PWMOutputDevice</text>
+<polygon fill="#298029" stroke="#298029" points="700,-36 596,-36 596,-0 700,-0 700,-36"/>
+<text text-anchor="middle" x="648" y="-15.5" font-family="Sans" font-size="10.00" fill="#ffffff">PWMOutputDevice</text>
 </g>
 <!-- Motor&#45;&gt;PWMOutputDevice -->
 <g id="edge13" class="edge"><title>Motor&#45;&gt;PWMOutputDevice</title>
-<path fill="none" stroke="black" stroke-dasharray="5,2" d="M564.573,-71.6966C572.202,-63.2198 581.523,-52.8636 589.876,-43.5826"/>
-<polygon fill="none" stroke="black" points="592.518,-45.8787 596.606,-36.1043 587.315,-41.1959 592.518,-45.8787"/>
+<path fill="none" stroke="black" stroke-dasharray="5,2" d="M573.218,-71.8761C585.923,-62.8931 601.664,-51.7625 615.423,-42.0341"/>
+<polygon fill="none" stroke="black" points="617.544,-44.8209 623.689,-36.1898 613.503,-39.1053 617.544,-44.8209"/>
+</g>
+<!-- Servo -->
+<g id="node15" class="node"><title>Servo</title>
+<polygon fill="#298029" stroke="#298029" points="675,-108 621,-108 621,-72 675,-72 675,-108"/>
+<text text-anchor="middle" x="648" y="-87.5" font-family="Sans" font-size="10.00" fill="#ffffff">Servo</text>
+</g>
+<!-- Servo&#45;&gt;PWMOutputDevice -->
+<g id="edge14" class="edge"><title>Servo&#45;&gt;PWMOutputDevice</title>
+<path fill="none" stroke="black" stroke-dasharray="5,2" d="M648,-71.6966C648,-63.9827 648,-54.7125 648,-46.1124"/>
+<polygon fill="none" stroke="black" points="651.5,-46.1043 648,-36.1043 644.5,-46.1044 651.5,-46.1043"/>
 </g>
 </g>
 </svg>