Re: 555 Circuit Help Needed

On Tue, 06 May 2008 08:41:18 -0700, Howard wrote:

Hello to all and thanks for reading. I am attempting to build a 555
circuit that will "listen" to audio output from a computer speaker (hard
wired to the speaker) and fire a relay and hold it for 5 seconds after
the music stops.

I put a Bowden 555 circuit together that fires the relay when a push
button is pressed and holds it for a 5 second time period.

I am looking for suggestions on a circuit that will replace the manual
push button, thus allowing the relay to remain energized while music is
playing.

Any help appreciated.

Search around the web for an "audio detector" circuit. You need to
rectify the audio and compare the DC level with a threshold. The output
of the comparator will "push the button". You may find that you'd want
to filter the audio first, to get the best missed event vs. false alarm
rate.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
.

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