Thread: momentary switch -> latching circuit?

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.

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

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.

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

DPDT Illuminated Pushbutton IP65 Red

DPDT Illuminated Pushbutton IP65 Green

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

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

Originally Posted by 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

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.

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

Originally Posted by 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

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??