Subject:
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Microphone on a Handyboard
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 27 Aug 1997 06:01:43 GMT
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Original-From:
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Randy Sargent <rsargent@newtonlabs!avoidspam!.com>
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Viewed:
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1292 times
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> Hi all, has anyone interfaced a microphone to an analog input of the
> HB? I've amplified the signal with an op-amp (LM386) but can't figure how
> to integrate the (AC) signal into a usable voltage range for the HB. I
> don't think that just rectifying the signal will work, but my electronics
> knowledge is sorely limited.
Assuming you've hooked the LM386's ground to ground and the + voltage to
5v, you should be set hooking the output of the LM386 to the analog input.
Do not insert a capacitor in series, as might be shown for hooking up the
LM386 to a speaker.
As I recall, the LM386 is pretty cool, because unlike other op amps, it
tends to center the output signal around half of the positive supply
voltage if you hook it up straightforwardly. This means that the voltage
you read from the A->D should be centered around a certain value when all
is quiet, and you should be able to see samples that go lower and higher
when there's noise.
Another advantage of the '386 (although not in this situation) is that it
has a high-current output; it can drive speakers or small motors. One
disadvantage, though, is that it's maximum gain is 200, which might not be
enough to get your microphone to make a big enough signal for the analog
input to measure easily -- depends on the microphone.
If you're not sure if you're getting a signal through to the A->D, try
blowing on the microphone or clapping right next to it. Both send really
strong signals.
-- Randy
----------------------------------------------------------------
Randy Sargent Newton Research Labs
Senior Design Engineer Robotic Systems and Software
rsargent@newtonlabs.com http://www.newtonlabs.com/
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