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