Momentary latching relay

Hi,

Im in a bit of a jam,

Given im very noobish when it comes to things like this my knowledge of circuit design go's about as far as one of those dick smith's kits.......


What im trying to achieve is a circuit then operates of a momentary switch that will ground or give + 12v to a relay and when i push the button a second time it will cut the circuit leaving the relay dead etc.

This entire circuit will preferable run off 12v dc as its needed for an automotive application.

Thanks in advance,

Dave.

You may not need any latching relay nor ÷2 circuitry if you can select a push-on push-off switch, like the ones usually meant for the rear glass defroster.

Yes i did consider this option, but it is for a cruise control unit.

The BCM usually handled this side of things, Im aiming to get all the functionality of the stalk control to work including the momentary on/off switch.

( cruise is from a different model car with a high end BCM, the car its going to has a low end bcm which does not support this feature )

Then build a divide by 2 circuit. There is many schematics on the net, like this one :
http://www.discovercircuits.com/DJ-Circuits/on-off-latch.htm
Search for latching switch or pushbutton.

I did and have found many simular, i was and still am unsure of what to use. I will give this one a go.

As i said my knowledge of circuits and circuit design is limited at best.

Externet said:

Then build a divide by 2 circuit. There is many schematics on the net, like this one :
http://www.discovercircuits.com/DJ-Circuits/on-off-latch.htm
Search for latching switch or pushbutton.

Click to expand...

Can you explain simply what a divide by 2 circuit is ? Im keen to learn.

Hi.
The single cycle of turning on - off the relay takes two pushes of the button. That takes 2 pulses into a 'divide by 2' circuit = 1 cycle. It is also called a flip-flop circuit.
The compfuser am now on has no Java and cannot confirm the link am supplying fits your question. I have seen many in that site before and are well made animations that should work for you.
Just give it a try and will check this thread later.

http://www.falstad.com/circuit/e-divideby2.html

That site is a wealth of tutorials.

Yes, checked that link. CLK is your pushbutton input; Q should be able to directly drive the cruise control input. The box shown as D flipflop can be half a 4013 integrated circuit. The link below shows the pinout in order to implement it; and powers directly from an automobile supply.
In other words, only one part to interface your single pushbutton to activate/deactivate the cruise. No relays should be needed.

http://commons.wikimedia.org/wiki/File:4013_Pinout.svg

I used a 556 timer wired as a flip flop in an automotive project and it worked great.

I built two similar circuit
http://docs.google.com/Doc?docid=0AbLPpongh6DzZDRtbnI5d185Zm52Z3o5Z2c&hl=it

http://andreapg.altervista.org/on-off.jpg

The first circuit works fine if the coil turns off within 0.003 seconds, so it can fail easily. Than I prefer the second solution.