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Waveform straight out of audio device is not really good, you need to pass it to a schmitt trigger, preferably HC-type (if you are using C-MOS ... HC has threshold around 2.5V (for VCC 5V), while HCT, has it much lower - so noise from audio device (there is some) may trigger it and then you will have multiple pulses. Or, you should use comparator (opamp with some positive feedback to have small hysteresis for noise immunity).
You have to have a look at waveform with oscilloscope to be sure what is really going on.
Last edited by bojan; 05-05-2012 at 07:40 AM.
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