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 teachtech@bc.sympatico.ca Vancouver,Canada Faster horses, younger women, older wiskey, and more money! ---------- | From: Nigel Orr | To: PICLIST@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