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