Relay to energize after 4 pulses

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Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=28416
Printed Date: July 15, 2025 at 12:39 PM

Topic: Relay to energize after 4 pulses

Posted By: cctyler
Subject: Relay to energize after 4 pulses
Date Posted: March 15, 2004 at 2:41 PM

Im trying to power a few extra sirens/peizos for my alarm, but I don't want the extra sirens to chirp when the regular siren chirps. I only want the extra sirens to go off when the alarm is triggered and the regular siren is going full tilt.

So I need a relay that can pass off 4 pulses (thats the maximum # of pulses my alarm gives off for any command, starter,warn away, arm) but once is sees a constant pulse, to stay energized.

Ex: when I disarm the alarm, I get 2 pulses from the siren output. When the alarm is triggered, I get a constant pulse from the siren output. The relay needs to ignore the pulses and only be activated when it sees the constant siren output.

Make sense? I was thinking about a timer relay, but I haven't seen many around. As long as the pulses weren't long enough that the relay counts them as seconds. Would using a cap and a resistor work just as well? I think it all depends on the length and interval of pulses correct?

Anyone than can help, much appreciated,

Thanks.

Replies:

Posted By: cctyler
Date Posted: March 19, 2004 at 3:44 AM

So I need something to delay the signal coming from the siren output. Can a cap and resistor do this?

Posted By: NowYaKnow
Date Posted: March 19, 2004 at 8:56 AM

You could try the diagram below. Basically if the alarm is armed and the door is open (ie: alarm going off) the extra sirens sounds. The first diagram assumes the door trigger in your car is positive. If your already using the ground out when armed for something else make sure to diode isolate it!

posted_image

Posted By: NowYaKnow
Date Posted: March 19, 2004 at 8:59 AM

Here's the diagram if you are using a negative door trigger in the car.

posted_image

Just an idea I have never actually tried this circuit but it should give you a starting point. It works in theory so give it a try and see what happens. Good luck,

Mike

Posted By: markcars
Date Posted: March 19, 2004 at 10:18 AM

This last circuit will sound the sirens only when a door is opened while alarm is armed. I think cctyler wants the sirens to sound on a full trigger, not just only when a door is opened. For example, when the shock sensor triggers the alarm, this won't sound the sirens.

It is a good starting point. Just more triggers need to be connected as required(with isolation for each of course). If you have dual-zone sensors, you can connect the second zone of each sensor to the relay input, connecting to where you see the -ve door trigger input. This way only a "full-tilt" like you put it will sound the extra sirens. I will try to put up an pic supplementing what you see above if I get the time to draw it.

Posted By: xetmes
Date Posted: March 19, 2004 at 10:59 AM

easiest way I would think of.. program a microcontroller to ignore any input that doesnt last a certain length. You could also set a monostable timer up for longer than each pulse, have the pulse trigger it then when finished check again, if it is still active the alarm must not be chirping, It may be hard to calibrate to be just right though.... just some ideas...