momentary switch -> latching circuit?

[Sprint]

had a look on google, but cant find anything that i can comprehend

basically i have 2 momentary pushbutton switches that i need to use to control 2 circuits, but ideally i would have a push on - push off latching switch.....

is there any way i can do this with a reasonably simple circuit?

[bee utey]

You can't just use latching push buttons? Jaycar SPST cat SP-0178. Otherwise look at heated rear window relays, I believe some cars have a momentary switch controlling such a relay. Also VW used latching relays back in the 70's to control their hi/lo from a simple momentary contact on the column stalk. Shouldn't be hard to find one.

[rovercare]

You need to explain what you are controlling, there is many ways of achieving what you want, but knowing what the cct needs to do, would be helpful:p

[Utemad]

The fog light switch on a 97-98 Disco1 is momentary with a latching relay of some kind. I found this out when I pinched one to use as a spotlight switch as my 94 model fog light switch isn't momentary.

[Blknight.aus]

first guess is that what you want is a DPDT latching push button switch.

DPDT Illuminated Pushbutton IP65 Red (http://www.jaycar.com.au/productView.asp?ID=SP0745&CATID=28&form=CAT&SUBCATID=652)

DPDT Illuminated Pushbutton IP65 Green (http://www.jaycar.com.au/productView.asp?ID=SP0749&CATID=28&form=CAT&SUBCATID=652)

both those are rated for 5A at 250Vac and have a 12v light in them to indicate they are on.

[Sprint]

alternative switches arent an option, im trying to keep to the factory switches which are, unfortunately, only momentary

for the purpose of this exercise, i need the momentary switch to turn a relay on with the first press and off witht he second

[mike_ie]

alternative switches arent an option, im trying to keep to the factory switches which are, unfortunately, only momentary

for the purpose of this exercise, i need the momentary switch to turn a relay on with the first press and off witht he second

At risk of pointing out the obvious, the solution is as simple as replacing whatever relay you are currently using for the fog lights with a latching relay. If your fog light setup isn't currently using a relay, then you now have an excuse to install one. The latching relay will be turned on and off by the pulse voltage from the momentary switch - no other circuitry is required.

There are plenty of other ways to do this, but they all boil down to building your own latching relay - a standard relay with a resistor and big capacitor comes to mind as a solution. But if you can buy an off the shelf latching relay, that's what I'd be doing. IF you can't get a big enough latching relay to drive your fog lamps directly, then you can use a small latching relay to drive the main fog light relay, thus avoiding the possibility of burning it out.

[Sprint]

who said it was for foglights?

problem with a latching relay, is that to my understanding, is that once you trigger it, you need to kill the power to turn the relay off

[mike_ie]

who said it was for foglights?

problem with a latching relay, is that to my understanding, is that once you trigger it, you need to kill the power to turn the relay off

Apologies, I took the word "foglights" from another post here. A standard relay only turns off when you cut the power to the coil, a latching relay on the other hand gets turned on by a 12v pulse (pressing the momentary switch), and turned off by the next 12v pulse (pressing the switch again). From what you describe, this is exactly what you want, no??

[pop058]

What about a simple changeover relay. One pulse to change it one way and the next to change it back. One set of contacts are used to do what ever you require and the other set left vacant ??

[mike_ie]

I knew that I had heard of them being used somewhere else before - Volkswagen Beetles use the same setup toggle between heads and dims.

Google gives me this:
http://www.oldvolkshome.com/headrelay.pdf


It is used on VW Beetles to toggle between low and high beams so it will handle a fair amount of current. It mechanically latches in alternating positions each time you push the switch connected to the terminal labeled "brown wire" in the drawing, with the other side of the switch connected to ground. The wire labeled white with black stripe would be connected to the +12V source thru an appropriate fuse. The coil is only energized when you push your switch.

[Sprint]

What about a simple changeover relay. One pulse to change it one way and the next to change it back. One set of contacts are used to do what ever you require and the other set left vacant ??

garden variety changeover relays wont work in this case, they only switch over while energised


hmm..... looks like its time to go to bed with a copy of the ashdowns book and hope the answer lies within

[mike_ie]

A little more googling tells me that the exact relay you are looking for is Relay "434" - 1C0 941 597. Apparently it's also used in Audi's.

[Blknight.aus]

Jaycar latching relay (http://www.jaycar.com.au/productView.asp?ID=SY4060&keywords=latching+relay&form=KEYWORD)

[bee utey]

who said it was for foglights?

problem with a latching relay, is that to my understanding, is that once you trigger it, you need to kill the power to turn the relay off

The VW headlight relay was used in Kombi's until at least 1979, that's probably the newest kombi I have dismantled in my youth. Visit your local pick-a-part style wrecker and look at all the early VW products on offer.

[mike_ie]

Jaycar latching relay (http://www.jaycar.com.au/productView.asp?ID=SY4060&keywords=latching+relay&form=KEYWORD)

Yeah, I took a look on Jaycar too and spotted that one.This is where it would be good to know what exactly you are trying to drive with this circuit. If it's a low current circuit, then there are more options available. On the other hand, if it's a high current application then the options are considerably narrowed down. Considering that you are using stock switches it could be heated seats, spotlights, fog lights, all which draw a decent number of amps. CAre to fill us in, or do we need to guess :p

[Basil135]

Yeah, I took a look on Jaycar too and spotted that one.This is where it would be good to know what exactly you are trying to drive with this circuit. If it's a low current circuit, then there are more options available. On the other hand, if it's a high current application then the options are considerably narrowed down. Considering that you are using stock switches it could be heated seats, spotlights, fog lights, all which draw a decent number of amps. CAre to fill us in, or do we need to guess :p

The other option is to use the Jaycar IC relay to drive another larger relay. Mind you, this starts to get a little trickier in the wiring, and you would probably need to enclose it all in a box -

Depending upon the application...:confused:

[VladTepes]

He's not saying because its one of those James Bond secret gadget missile kind of things....

[rogan]

Special Applications with SPDT Relays, Diagrams (http://www.the12volt.com/relays/page5.asp#lsp)

[mike_ie]

He's not saying because its one of those James Bond secret gadget missile kind of things....

Dunno, how much current does an ejector seat draw??? :confused:

[Blknight.aus]

oh about an amp or so to initiate the explosives.

[Sprint]

havent listed the end use because atm i havent decided exactly what i want to run from the circuit, but for the purpose of this, imagine i want to trigger a regular automotive relay..... from that i can turn on/off whatever i need to

what i am certain of, is that i have no other use for a momentary switch, but the bezel and switches are available to take up what would otherwise be a blanking panel

[mike_ie]

havent listed the end use because atm i havent decided exactly what i want to run from the circuit, but for the purpose of this, imagine i want to trigger a regular automotive relay..... from that i can turn on/off whatever i need to

what i am certain of, is that i have no other use for a momentary switch, but the bezel and switches are available to take up what would otherwise be a blanking panel

Then the easiest solution is to grab one of the VW relays I described earlier, and wire the switch directly to that. Next easiest solution, grab one of the Jaycar latching relays, and use that to drive the coil of a standard automotive relay.

[Sprint]

considering where i am, it's gonna be easier to hit the local jaycar shop than find a wrecker with VW's.....

[mike_ie]

Dammit, I did a bit more digging on the Jaycar relay and fond that it's not a true latching relay. The pdf they provide doesn't give a pinout of the relay, however the following link does:

http://info.tactnet.co.jp/shinmei/e/product/pdf/E_RSB.pdf

Pin 1 is coil 1 positive (12v)
Pin 16 is coil 1 negative
Pin 2 is coil 2 positive (12v)
Pin 15 is coil 2 negative

Why two coils? If you apply momentary 12V to coil 1, the contacts will "set" (toggle) to the other position and stay there, even if you disconnect the 12V.
If you then apply a momentary 12V to coil 2, the contacts will "reset" (toggle back) to the original position.

In other words, you can't operate this relay with a single momentary switch, which you want to do :( So it's back to the VW relay until I find something else.

You can do it with for standard relays seriesed up..... else we're getting into the realm of more complex circuitry....

[mike_ie]

Alright, how good is your understanding of electronics, because there are a couple of ways of doing this. If you know anything about IC's, then the simplest is to use a 7404 hex inverter from Jaycar to toggle a standard relay on and off with a pushbutton circuit.

[sniegy]

Like the rest of us, I am not sure what you want to do, But from just turning on relay, why not just buy (i will assume you have either a D1 or D2 as you do say factory switches that are momentry) (this is all James Bondish isnt it;)) the latching switches from a wrecker/dealer. They are all the same size (you may have to shave the alignment tags as they are tagged to go into certain slots) & the front covers come off & can be replaced with a blank cover(from the one you remove) & be tagged anyway you like).
D1 Driving light or rear wiper switch
D2 cruise control switch

They arent that expensive.

Cheers.

[paulz]

I went through a similar exercise with original Disco momentary switch(es) for reversing/work light and spots using the Jaycar latching relay. For a high current application the latching relay can drive another automotive relay. You can find a simple circuit in siliconchip.com.au May 2010 - circuit notebook. Uses the Jaycar latching relay, with a couple of diodes, resistors and capacitors. Cheap and the relay only draws current when being switched ie/ momentary

[VladTepes]

Lets say I wanted to do a similar thing to this thread - using momentary swirches - one in dash and one at rear of vehicle - driving a rear work light. What would I need and how to wire it ?

It would need to be able to be switched on AND off from either or both switches.
(that is, ON at dash then OFF at dash or ON at dash then OFF at rear or...)

[Blknight.aus]

youd use a pair of push to change SPDT switches.

[paulz]

Lets say I wanted to do a similar thing to this thread - using momentary swirches - one in dash and one at rear of vehicle - driving a rear work light. What would I need and how to wire it ?

It would need to be able to be switched on AND off from either or both switches.
(that is, ON at dash then OFF at dash or ON at dash then OFF at rear or...)
No problem, switching dash and rear of vehicle use the siliconchip.com.au May 2010 circuit put forward in above July 2010 post. The only change is to wire both your momentary switches (dash + rear) in parallel; that is both switches connected to same point in circuit.