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Will play the C above middle 'C'. Type
0 0 beep <exe>
to end it.
4.2.4 Audio In
The FIGnition Audio circuit is also designed to be able to sample 1-bit digital audio inputs.
In this case, Port D6 is set up as an input and audio from a computer, MP3 player or other
audio device is set to play a simple audio encoding of digital data.
Here, it works in the opposite direction. The two resistors hold the voltage at about 2.5v.
An audio input has a waveform which ranges from +1v to -1v. A +1v peak of a wave
charges capacitor C7 by an extra 1v, raising the input voltage to 3.6v, enough to be read
as a 1 by the AVR. This voltage then decays over time towards 2.5v. A -1v will then dis-
charge the capacitor by -1v lowering the input voltage to 1.5v; low enough to be read as a
0 by the AVR.
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