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Need Help with simple Automotive Circuit

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Live4Redline

New Member
I'm trying to make a simple circuit module that i can tie into an already existing push button switch that will turn ON/OFF an external relay. I've looked into getting a latching relay for the task but i can't find anything that match's my needs.

Its a 12v relay that I'm trying to activate with a 5v signal from the push button switch. When i push the button i want it too turn the relay on and hold it on. When I push the button again i want it too turn the relay off. Rinse and repeat.

It seems like a simple task but i can't figure out what I need to make it happen. I'd also like to try and make this as cheap and RadioShack friendly as i can.



Does anyone think they can give me a hand? I would be greatly appreciative.
 

MikeMl

Well-Known Member
Most Helpful Member
Any chance you will settle for two buttons: One to turn on the relay, the other to turn it off?
 

MikeMl

Well-Known Member
Most Helpful Member
That makes it harder. Are you familiar with a CMOS D flipflop (74HC74, or 4000 series equiv)?
 

MikeMl

Well-Known Member
Most Helpful Member
Ok, more questions. Is the existing switch a mechanical snap-action switch (i.e. does it click audibly when pushed)?

How many poles does it have? (spare pins on the back that are not wired)?

In the existing circuit, is one end of the switch connected to ground or to 5v?

Can you use the existing 5V to power the extra logic (just a few mA; the 12V relay will not be powered by the 5V)?
 

dougy83

Well-Known Member
What about a little relay logic? Have a look at the attached circuit. It works (I hope it works) with a clean switch contact; if you only have the switched 5V signal, then use an additional 5V relay to provide the clean switch contact.
 

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MikeMl

Well-Known Member
Most Helpful Member
What about a little relay logic?...
That presumes that he has a spare set of switch contacts that are not already being used to switch something else. That is not the impression I got...
 

Live4Redline

New Member
Ya... the switch i'm required to use is already in place and thats half the problem. Its a two pole switch that when pressed makes contact between the sig wires and tells the controler that the button has been pushed. It may be easier to just swap the operating voltage to 12v so that i don't get any odd side effects from the controller.

Now i liked Mike2545's idea... i'm not 100% sure how i would have to wire in the entire thing and if it would work for a 12v line as well.
 

KMoffett

Well-Known Member
Here is a unique little 12v push-on/push-off relay circuit that might work for you.

Ken
 

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