visus
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teensy-audio


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