Horn Circuit Timer

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=73404
Printed Date: May 06, 2024 at 5:19 PM

Topic: Horn Circuit Timer

Posted By: pjs826
Subject: Horn Circuit Timer
Date Posted: February 24, 2006 at 7:29 AM

I'm glad I happened upon this site. It seems as if there is plenty of good information here.

I installed Remote Keyless Entry on a 1994 Grand Am. It was a basic system. I added a couple relays and tied the parking lamps into the unlock circuit and the horn into the lock circuit. The parking lamps work fine, but the horn seems to blow for about two seconds. I would like to cut the horn time down to a chirp, if possible. I've read about 555 timers, but they seem a little involved.

I was wondering if I couldn't cut down the time the horn sounds by installing a capacitor and resistor on the coil side of relay #1.

I've included my schematic and a capacitor schematic.

Will the capacitor and resistor work to cut down my time? I'm not sure of the size of the capacitor or resistor. Any ideas?

Thanks.

posted_image

Replies:

Posted By: tacalin
Date Posted: February 24, 2006 at 10:42 AM

100 uF and 220 Kohm.

Posted By: pjs826
Date Posted: February 24, 2006 at 8:46 PM

tacalin wrote:

100 uF and 220 Kohm.

Thanks.

Is there some formula to arrive at these numbers? or is it practical working experience?

Posted By: dualsport
Date Posted: February 24, 2006 at 10:02 PM

You can get a rough idea by multiplying the resistance of your relay coil by the value of the capacitor-
If for instance your relay coil is 750 ohms, multiply it by 100E-6 (100 divided by 1 million), to get an approximate time, in seconds, that it will pulse. Just for a ballpark approximation-

The resistor doesn't affect the really time of the pulse much, but it does control how long it will take for the circuit to reset itself after your control input is removed, and allow you to pulse the relay again.

If you use a very large resistor, you have to wait a longer time to allow the capacitor to discharge before you can pulse it again. If you use too small a value though, then you start affecting the timing of the pulse, making it shorter.

Posted By: pjs826
Date Posted: February 25, 2006 at 7:14 AM

Thank you.

Hopefully, I'll be fixing this today.

Posted By: pjs826
Date Posted: February 25, 2006 at 1:55 PM

All finished.

Installed a 10K ohm resistor and a 470uF capacitor. Horn chirp is perfect. Not too long or loud.

Thanks for the help. posted_image