Switch 120V AC triggered by audio

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Switch 120V AC triggered by audio

Post by markcox » Wed Feb 18, 2004 8:08 pm

At work our alarm system sounds an audible alarm (horn) My boss wants to have it trigger a strobe light also. Its in a really noisy enviroment so the persons working there might not here an alarm. Is there an easy way to turn on the strobe by using the audio signal? My boss thinks you can just hookup a stobe light and it will work. Anyway I was thinking of a relay but I don;t believe audio will be able to drive it. <p>Would anyone have a circuit for this type thing?<p>Thanks

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Re: Switch 120V AC triggered by audio

Post by myp71 » Wed Feb 18, 2004 9:11 pm

Try "the clapper" maybe the alarm will trigger it :D :D <p> -

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Re: Switch 120V AC triggered by audio

Post by Chris Smith » Wed Feb 18, 2004 9:31 pm

Use the same power to run and trigger both.

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Re: Switch 120V AC triggered by audio

Post by Edd » Thu Feb 19, 2004 11:26 am

You might have to drop a couple of front bezel screws to investigate this. The way you worded it sounds like this is not a dedicated speaker/horn associated with your PA system. Instead it is a dedicated alarm transducer only, and these are normally actuated from a 24VAC control line fed to them. If, perchance the units type happens to be the popular fire engine red FEDERAL brand, older units typically used the Klaxxon horn……(submariners-DIVE_DIVE_DIVE)…or the later units versions have contained an internal electronics alarm generator circuit (with several optional tonal sequences) and its power driver circuitry feeding a hefty internal all weather speaker.
If this is your case , a version of this unit is made WITH a strobe flash mounted on the front of the units grill. This should be available surplus from an alarm installer, etc. About 6 months ago our monthly electronics fleamarket produced 3 of the newer units for me at a buck a pop…..I only wanted their strobe units.<p>73's de Edd
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Re: Switch 120V AC triggered by audio

Post by markcox » Fri Feb 20, 2004 7:59 am

Thanks for the reply's
After some more investigation it seams this it is a horn type of system I measured 12.7v DC while the horn was on and 1.3 while it was off It pulses about every 2 sec.<p>I wish to switch 120vac using that input. Is there an easy way to hold the relay on while the 12v is pulsing? I was thinking a capacitor might hold the relay on long enough?<p>Thanks

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Re: Switch 120V AC triggered by audio

Post by MrAl » Fri Feb 20, 2004 10:09 am

Hello there,<p>If you use a diode and capacitor that
might work. Diode anode to +12v signal and
cathode to cap + terminal.
The cap you will need has to provide a
time constant of about 3 seconds, so measure
the resistance of your relay and divide
3 by that resistance (ohms) to get the cap
value (farads). You should have a relay
that has a 12v dc coil and contacts rated
at 120vac for whatever current you need.<p>Take care,
LEDs vs Bulbs, LEDs are winning.

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Re: Switch 120V AC triggered by audio

Post by dacflyer » Sat Feb 21, 2004 9:30 am

ok,, i work on strobes a lot here for general and aircraft....even the runway landing strobes you see flashing in a line... then things are huge!
upto 1,500 volts with a 10k trigger
most strobes have to have a sec or so to charge up before able to flash,,especially the cheap ones. you can find 12 volt strobes...but they are usually puny , and the good ones are expencive and require more current...
you might be more apt to use a 12volt relay and a 500watt light...the outdoor quartz type maybe?
that way you get a fast responce... and its still bright too.... hope this helps ya...let me know

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Re: Switch 120V AC triggered by audio

Post by jollyrgr » Wed Feb 25, 2004 3:42 pm

What type of alarm is this for? There should be some sort of switch closure, constant source, etc. that goes live while the alarm is being sounded. <p>Aside from that, I'd go with an optocupler or solid state AC relay. Here is an example of a solid state relay:<p>http://www.allelectronics.com/cgi-bin/c ... RLY-41U&ty pe=store<p>You would place a cap in parallel to the "coil" input of the relay. Isolate the relay and capacitor by using a series diode. This will prevent the horn from drawing power out of the diode but allow the relay to remain energized.<p>Check the RELAYS section at the above link for more versions.<p>You could also use a high power relay from an automotive parts store if you only plan on switching 12 or so volts. These are found near the stereos and with the other electronic switches, wiring, etc. Get a "generic" relay used for off road lighting. The car specific relays are often quite expensive.<p>As far as using a strobe light....<p>You could parallel a 12 volt strobe light with the horn as is.<p>[ February 26, 2004: Message edited by: Jolly Roger ]</p>
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Re: Switch 120V AC triggered by audio

Post by rsteortz » Tue Mar 09, 2004 8:02 pm

Hey Mark,
Check the voltage on the horn when it alarms. It could be AC or DC. Then find a strobe unit that works on the same voltage then wire it across the horn.

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