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51 lines
2.2 KiB
51 lines
2.2 KiB
8 years ago
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<script type="text/x-red" data-help-name="AudioOutputPWM">
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<h3>Summary</h3>
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<div class=tooltipinfo>
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<p>Transmit audio using Teensy 3.1's PWM pins. Two pins are
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used for coarse and fine pulses, to be combined by scaled
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resistors.</p>
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</div>
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<h3>Audio Connections</h3>
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<table class=doc align=center cellpadding=3>
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<tr class=top><th>Port</th><th>Purpose</th></tr>
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<tr class=odd><td align=center>In 0</td><td>Audio Channel</td></tr>
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</table>
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<h3>Functions</h3>
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<p>This object has no functions to call from the Arduino sketch. It
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simply streams data from the its input port to the PWM pins.</p>
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<h3>Hardware</h3>
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<p>The following circuit is recommended.</p>
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<p align=center><img src="img/pwmdualcircuit.jpg"></p>
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<p>Signal range is approx 1.55 Vp-p.</p>
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<p>These resistor values assume approx 20 ohms output impedance
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on the digital pins. The 127K resistor may be adjusted or
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trimmed for variation in output drive and tolerance on the
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475 ohm resistor.</p>
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<p>A plastic film (Polypropylene, Polyethylene, Polyester, etc) or
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C0G/NPO ceramic capacitor should be used for filtering. Low
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quality ceramic (X7R, Y5V, Z5U, etc) can cause signal distortion.</p>
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<h3>Examples</h3>
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<p class=exam>File > Examples > Audio > HardwareTesting > PassThroughMono
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</p>
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<h3>Notes</h3>
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<p>This object only works properly when Tools > CPU_Speed is set to
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48 or 96 MHz. Other speeds aren't supported and will likely fail
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in strange ways.</p>
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<p>The PWM carrier frequency is 88.2 kHz. The suggested circuit
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will only slightly filter the carrier. Extra filtering will be
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required for a clean signal without the ultrasonic PWM carrier.
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</p>
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<p>Analog signals created by filtering PWM waveforms use the digital
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power supply as their reference voltage. Any noise on the digital
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power line can directly couple to the output signal. The built-in DAC or
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<a href="http://www.pjrc.com/store/teensy3_audio.html" target="_blank">audio shield</a>
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should be used when higher quality signals are needed.</p>
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</script>
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<script type="text/x-red" data-template-name="AudioOutputPWM">
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<div class="form-row">
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<label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
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<input type="text" id="node-input-name" placeholder="Name">
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</div>
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</script>
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