timeing circut from pulse

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=780
Printed Date: June 11, 2024 at 7:04 AM

Topic: timeing circut from pulse

Posted By: bensalvage
Subject: timeing circut from pulse
Date Posted: May 15, 2002 at 9:37 AM

I want to turn a relay on and keep it on for about 4 seconds or so. I want to trigger this from a pulse of my remote. I know there is a circut for a relay that shuts itself off after 3 seconds, but that is with a constant source. I need to shut it off with just a single pulse.

-------------
Ben

Replies:

Posted By: Big Dog
Date Posted: May 15, 2002 at 10:11 AM

Hey Ben,

Here's what you can do....place a 4700mfd polarized cap on the coil of a relay, pins 85 and 86. If the trigger out from your module is negative the make sure it goes to the negative of the cap and the positive of the cap would go to B+ direct. Now you may wire pin 30 as your output and 87 as your input either to ground or B+. This set-up should give you about 3 seconds. Increase cap or add another in parallel to increase time.

-------------
Prepare your future. It wasn't the lack of stones that killed the stone age.

Posted By: Thinkster
Date Posted: May 16, 2002 at 2:10 AM

There is a circuit to do this. It's called a one-shot or monostable multivibrator. You can use an LMC-555 IC with a few resistors and capacitors (which you calculate the values of depending on the amount of time you need) here's some info on that IC: https://www.learn-c.com/lmc555.pdf

I have built many of these circuits for many different timer applications. These chips have 100's maybe even 1000's of applications!