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PICList Thread
'Voice operated switch'
1999\01\18@012146 by Steve Ridley

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Hello PICsters

I would like to build a circuit to detect whether someone has spoken into a
microphone. Basically I have a PIC based message recorder and I want to know
if the user has said anything or not. I think this is called a "voice
operated switch". The switch needs to generate a logic level that I can
detect at a PIC input. This circuit does not have meet rigorous standards
and the less components the better. Any ideas ?

Steve Ridley
Blue Ocean Telecommunications

1999\01\18@032605 by Gerhard Fiedler

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At 17:23 01/18/99 +1100, Steve Ridley wrote:
>I would like to build a circuit to detect whether someone has spoken into a
>microphone. Basically I have a PIC based message recorder and I want to know
>if the user has said anything or not. I think this is called a "voice
>operated switch". The switch needs to generate a logic level that I can
>detect at a PIC input. This circuit does not have meet rigorous standards
>and the less components the better. Any ideas ?

how's an opamp with a diode as a precision rectifier, followed by a RC low
pass, and then into a schmitt trigger input of the pic?

ge

1999\01\18@064705 by Nigel Orr

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At 17:23 18/01/99 +1100, you wrote:
>I would like to build a circuit to detect whether someone has spoken into a
>microphone. Basically I have a PIC based message recorder and I want to know
>if the user has said anything or not. I think this is called a "voice
>operated switch". The switch needs to generate a logic level that I can
>detect at a PIC input. This circuit does not have meet rigorous standards
>and the less components the better. Any ideas ?

Have a look at the 16c62x range, with analogue comparators.  I've had them
reliably triggering on a mic level signal, with no external circuitry at
all!  You can even bring one of the comparator outputs out on another pin
for debugging.

Nigel

1999\01\18@092545 by Mike Keitz

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On Mon, 18 Jan 1999 00:24:45 -0800 Gerhard Fiedler <spam_OUTlistsTakeThisOuTspamHOME.COM>
writes:

>how's an opamp with a diode as a precision rectifier, followed by a RC
>low
>pass, and then into a schmitt trigger input of the pic?

I would try a simple circuit first, then make it complicated only if
necessary.  First you may need to add an an amplifier to get a signal of
3 or 4 Vpp.  Apply the signal through a capacitor and 100K resistor in
series to a PIC input pin.  Connect a 1 M resistor from the pin to
ground.  With no signal, the 1 M resistor holds the pin low.  When signal
is present, the protection diode helps rectify it so peaks reach the high
threshold of the pin.  Software samples the pin rapidly and if it reads
high, starts or resets a timer that indicates voice is present.  In
effect the software acts as another rectifier diode, low pass filter and
shcmitt trigger combination.  PIC pins will tolerate "analog" inputs OK.
The PIC may draw a couple mA more Vdd current due to the partly biased
pin, but only while signal is present.


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1999\01\18@094659 by WIL REEDER

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Hi Nigel & original post
I have heard of using piezo disk directly on a pin as a sound activated
wake up for PIC.
I use vox circuits regularly and the simplest set up is just a mike and 1
transistor preamp with a rectifier on the output! sometimes a small load is
required (1m0) to allow the rectified voltage to decay in an appropriate
time frame. I think that Bob Blick has a preamp on his site that would work
for you (bobblick.com I believe)
Hope this helps


Wil Reeder
.....teachtechKILLspamspam@spam@bc.sympatico.ca
Vancouver,Canada
Faster horses, younger women, older wiskey, and more money!
----------
| From: Nigel Orr <nigel.orrspamKILLspamNCL.AC.UK>
| To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
| Subject: Re: Voice operated switch
| Date: Monday, January 18, 1999 3:45 AM
|
| At 17:23 18/01/99 +1100, you wrote:
| >I would like to build a circuit to detect whether someone has spoken
into a
| >microphone. Basically I have a PIC based message recorder and I want to
know
| >if the user has said anything or not. I think this is called a "voice
| >operated switch". The switch needs to generate a logic level that I can
| >detect at a PIC input. This circuit does not have meet rigorous
standards
| >and the less components the better. Any ideas ?
|
| Have a look at the 16c62x range, with analogue comparators.  I've had
them
| reliably triggering on a mic level signal, with no external circuitry at
| all!  You can even bring one of the comparator outputs out on another pin
| for debugging.
|
| Nigel

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