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PICList Thread
'Help connecting a microphone to a PIC'
1997\09\24@133616 by Hisham Abboud

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Hello,

I have an application which requires that a PIC
microcontroller monitor the volume level on a microphone.
It doesn't need to record or anything, simply monitor
the volume level and take some action based on whether
the level is above or below a certain threshold.
This cannot be done with a comparator since the threshold
can be set at will by software inside the PIC.

Are there any schematics available on how to connect
a microphone to the A/D port of a PIC?  Do I need a
pre-amp?  What else would I need?

Thanks in advance.

               Hisham.


--------------------------
Hisham A. Abboud
Cedrus Corporation.         On the Web: http://www.cedrus.com

1997\09\24@180904 by Steve Smith

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Use a simple duel op-amp to give some gain to the mic and then drive a the
second op-amp as a presicion rectifier to charge a cap on an analouge input
this is a simple VU meter / PPM meter giving an analouge output to a '71 or
similar. Gives a proportinal voltage to sound presure level (loudness). cost
is low <$0.30

Cheers Steve.....

1997\09\24@185222 by Harrison Cooper

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ok....how about making a window monitor....using two opamps, with a
digital pot controlled by the micro?

{Quote hidden}

1997\09\25@031738 by Keith Dowsett

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At 13:36 24/09/97 -0400, you wrote:
>Hello,
>
>I have an application which requires that a PIC
>microcontroller monitor the volume level on a microphone.
>It doesn't need to record or anything, simply monitor
>the volume level and take some action based on whether
>the level is above or below a certain threshold.
>This cannot be done with a comparator since the threshold
>can be set at will by software inside the PIC.
>
>Are there any schematics available on how to connect
>a microphone to the A/D port of a PIC?  Do I need a
>pre-amp?  What else would I need?
>
>Thanks in advance.
>
>                Hisham.

One solution occured to me. If you want to avoid a-to-d the cheapest
solution is to use a software pwm and a comparator. Of course this assumes
you have enough idle time/interrupts to run PWM.

The rectified audio signal is used to charge one RC system, and the pwm from
the PIC to charge another. The comparator simply compares the two values.

If you already have an op-amp to amplify the microphone you could probably
replace it with a dual op-amp for only a few cents, then use the second op
amp as a comparator (no feedback, but beware of offset voltages). Using a
quad op-amp would allow you to use one as a precision rectifier too.

Just my early morning musings,

Keith.

------------------------------------------------------------
Keith Dowsett         "Variables won't; constants aren't."

E-mail: kdowsettspamKILLspamrpms.ac.uk  or .....kdowsettKILLspamspam.....geocities.com

WWW: http://kd.rpms.ac.uk/index.htm
    www.geocities.com/CapeCanaveral/Lab/8979

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