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+<html devsite>
+  <head>
+    <title>Light Testing Circuit</title>
+    <meta name="project_path" value="/_project.yaml" />
+    <meta name="book_path" value="/_book.yaml" />
+  </head>
+  <body>
+  <!--
+      Copyright 2017 The Android Open Source Project
+
+      Licensed under the Apache License, Version 2.0 (the "License");
+      you may not use this file except in compliance with the License.
+      You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+      See the License for the specific language governing permissions and
+      limitations under the License.
+  -->
+
+
+
+<p>
+The file <a href="http://developer.android.com/downloads/partner/audio/av_sync_board.zip">av_sync_board.zip</a>
+contains CAD files for an A/V sync and latency testing
+printed circuit board (PCB).
+The files include a fabrication drawing, EAGLE CAD, schematic, and BOM. See <a
+href="latency.html">Audio Latency</a> for recommended testing methods.
+</p>
+
+<p>
+This PCB
+can be used to help measure the time between flashing the device's
+notification LED or screen backlight, vs. detecting an audio signal.
+When combined with a dual-channel oscilloscope and suitable test app,
+it can show the difference in time between detecting the light and audio.
+That assumes the LED or backlight response time and light detector's response time
+are negligible relative to the audio.
+</p>
+
+<p>
+This design is supplied "as is", and we aren't be responsible for any errors in the design.
+But if you have any suggestions for improvement, please post to the <a
+href="https://groups.google.com/forum/#!forum/android-porting">android-porting</a> group.
+</p>
+
+<p>
+Of course, this is not the only (or necessarily best) way to measure A/V sync and latency,
+and we would like to hear about your alternative methods, also at android-porting group.
+</p>
+
+<p>
+There are currently no compatibility requirements to use this particular PCB.
+We supply it to encourage your continued attention to audio performance.
+</p>
+
+<h2 id="images">Images</h2>
+
+<p>
+These photos show the circuit in action.
+</p>
+
+<img style="margin:1.5em auto" src="/devices/audio/images/breadboard.jpg" alt="breadboard prototype" id="figure1" />
+<p class="img-caption">
+  <strong>Figure 1.</strong> Breadboard prototype
+</p>
+
+<img style="margin:1.5em auto" src="/devices/audio/images/pcb.jpg" alt="an early run of the PCB" id="figure2" />
+<p class="img-caption">
+  <strong>Figure 2.</strong> An early run of the PCB
+</p>
+
+<img style="margin:1.5em auto" src="/devices/audio/images/display.jpg" alt="example display" id="figure3" />
+<p class="img-caption">
+  <strong>Figure 3.</strong> Example display
+</p>
+
+<p>
+This image
+shows the scope display for an unspecified device, software release, and test conditions;
+the results are not typical and cannot be used to extrapolate to other situations.
+</p>
+
+<h2 id="video">Video</h2>
+
+<p>
+This <a href="http://www.youtube.com/watch?v=f95S2IILBJY">Youtube video</a>
+shows the breadboard version testing circuit in operation.
+Skip ahead to 1:00 to see the circuit.
+</p>
+
+  </body>
+</html>