Use a tone detector and a microphone preamp (can be bandpass at the same
time). Tone detector can be 567 or CD4046, preamp LM358 is enough. Is the
buzzer the loudest source around ?

Peter

On Thu, 15 Aug 2002, Patric Anveg=E5rd wrote:

>Hi,
>
>I am currently evaluation different options to be able to recognice a
>buzzer sound from a speaker. For different reasons i would prefer to do
>this with passive electronics only. Does anyone have any experience with
>this kind of problem? It is only one buzzer signal that I need to detect.
>The frequency is unknown at the moment... As an output from the passive
>electronics I would like to have a change in the logic voltage level.
>Since I am really not an expert (by far) on analog electronics I have
>really only found one suggestion that I think might work: Band pass the
>speaker signal at the buzzer frequency and than integrate the signal to
>be able to accept the signal after a certain amount of time.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads