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555 Circuit Help Needed

H

Howard

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.
 
J

Jim Gregory

Howard said:
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.

You will need to modify /lengthen the 'audio' presence after amplifying it
to 'crushing' and rectifying its envelope to a DC level. Then, by a RC time
constant with electrolytics, make sure it ramps up fast and discharges
(decays) slower. This 'stretched' DC level will have to be amplified enough
to hold a relay on for about 5 secs. That's the gist. The 555 timing
function might be superfluous when audio is punchy and continuous.
Jim
 
L

LVMarc

Howard said:
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.

5 seconds is pushing the slow side and the R values to thelimimts. You
may want to add counter or use a time delay chip more suited to
##seconds, LSI logic makes a fine series of these delay timers...

Marc
 
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