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Simple timer circuit needed to control relay in Car.

 
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wingnut
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Joined: 18 Jul 2009
Posts: 1

PostPosted: Sat Jul 18, 2009 2:55 am    Post subject: Simple timer circuit needed to control relay in Car. Reply with quote

Hey guys

A mate brought a new car the other day. the previous owner has installed some extra security. A small hidden switch that controls a relay turning the fuel pump on/off.

Then problem is he has to wait for the turbo timer to do its thing before he can cut power to the fuel pump.


So I need some help designing a circuit that does the following:
- when switch is on ===> relay is on
- when switch is off ===> stay on for 2 mins, then turn off.
and it should run on 12volts.

I thinking of using a 555 timer but am not really sure how.

It should be quite simple but i can't get my head round it,, any help would be much appreciated.

Cheers
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Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Tue Jul 21, 2009 12:23 pm    Post subject: Re: Simple timer circuit needed to control relay in Car. Reply with quote

wingnut wrote:
Hey guys

A mate brought a new car the other day. the previous owner has installed some extra security. A small hidden switch that controls a relay turning the fuel pump on/off.

Then problem is he has to wait for the turbo timer to do its thing before he can cut power to the fuel pump.


So I need some help designing a circuit that does the following:
- when switch is on ===> relay is on
- when switch is off ===> stay on for 2 mins, then turn off.
and it should run on 12volts.

I thinking of using a 555 timer but am not really sure how.

It should be quite simple but i can't get my head round it,, any help would be much appreciated.

Cheers


You could use a 555 but it would probably be simpler to just charge a cap when ACC is turned on and have the cap keep a transistor biased. The transistor would then use hard power to energize the fuel relay.

This way when the ACC was removed the cap would slowly discharge and eventually turn off the transistor and the relay would drop out.
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