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Simple timing circuit

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=766
Printed Date: July 23, 2025 at 3:13 AM


Topic: Simple timing circuit

Posted By: kleenaccord45
Subject: Simple timing circuit
Date Posted: May 14, 2002 at 10:29 AM

Anybody know how to get 7 sec. of +12volts from a constant source. A basic Timer circuit. I am thinking a capacitor or something of the sorts.



Replies:

Posted By: Big Dog
Date Posted: May 14, 2002 at 12:01 PM

Hey KleenAccord,

A simple timer could be built using a relay and two 4700mfd polarized caps.

Go here https://www.the12volt.com/relays/page5.asp and look at constant to momentary.  To lengthen the time replace the 1mfd with two 4700mfd polarized caps being careful to observe polarity.  Should give you about 7 secs.  Add another cap for extra time as needed.



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




Posted By: kleenaccord45
Date Posted: May 22, 2002 at 2:22 PM
OK

I went to RadioShack and got a 4700M Farad cap.(5.99 about the same diameter as a quarter)
I wired as follows

87- went to +12 (AT THE BATTERY)
30- My output
85- went to the top of the cap and the of the resistor
the bottom of the cap and the other side of the resistor went to GND (AT THE BATTERY)
86- this was my trigger - I gave it +12 (AT THE BATTERY)

My output remained at 12.58 for several minutes -NOT SECONDS.

Where did I go Wrong?
I am thinking that the cap bought is way to big

posted_image




Posted By: the12volt
Date Posted: May 22, 2002 at 2:25 PM
What size resistor did you use?




Posted By: kleenaccord45
Date Posted: May 23, 2002 at 7:15 AM
10k




Posted By: the12volt
Date Posted: May 23, 2002 at 8:19 AM

Hi Kleenaccord45, the values you've listed should be correct and it sounds like the resistor isn't bleeding off the charge of the cap and may be bad or have a poor connection. Double check the value of the resistor and your connections at the resistor and/or try another one.

the12volt 






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