How do I make a " momentary switch " work like a continuous-current switch?

[LieutenantCracker]

I want to make a " momentary switch (button)" work as continuus-current switch-- in the same way that a typical rear-window defroster button works, in a car; INSTEAD of using a toggle, rocker, or clicking-pushbutton, continuous - current switch.

Obviously there'd be a relay involved but, how would I wire a controller, such as this?
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SKIN PROBLEMS FORUMS

[shorod]

A typical rear window defroster switch is also on a timer. Are you wanting something that is on a timer, or a momentary switch that is a press to turn on, press again to turn off? How much current are you looking to switch? Are you wanting something off-the-shelf, or something you would build?

-Rod

[LieutenantCracker]

No, not something on a timer-- I just used the defrose button as an example.

I imagine building it myself would be more economical, as I have little to no money to spend @ the moment... or in the forseeable future. I already have several of this type of switch / button-- even ones specifically from from Grand Marquis' and Crown Vic's (traction control [full-size button], rear window defrost; as well as some two-wire lead buttons = trunk open, trac ctrl, fuel door, etc).
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Lovely Wendie99

[LieutenantCracker]

. . . . . Oh, forgot to answer your 1st question: I'm not exactly sure how much current I'd be running. It would be for two medium-sized, and two small halogen fog / driving lights.
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Brunette Pregnant

[RahX]

Just curious, not trying to discourage or attack, are you trying to make it blend with the rest of the buttons already in the vehicle? I could probably look at a diagram on Monday for the T/C or something similar and see how the button actually operates XXX device.

[danielsatur]

A gate signal on a SCR can trigger an electronic circuit to turn on.

[shorod]

Originally Posted by danielsatur

A gate signal on a SCR can trigger an electronic circuit to turn on.

Yeah, the only problem with that in a DC application is the source voltage would need to be removed to toggle the device off. So the circuit would need to be provided its source current from an ignition switched circuit. One press of the momentary switch would turn the device on, but a subsequent press would NOT turn it off. The ignition key would need to be cycled to turn it off. If that is fine for this application, that's a relatively inexpensive solution. If he needs the on/off capability we'll need to try something different.

-Rod

[Selectron]

Originally Posted by LieutenantCracker

I want to make a " momentary switch (button)" work as continuus-current switch-- in the same way that a typical rear-window defroster button works, in a car; INSTEAD of using a toggle, rocker, or clicking-pushbutton, continuous - current switch.

Obviously there'd be a relay involved but, how would I wire a controller, such as this?

What you're looking for is a latching relay circuit. If you're not restricted to the use of just one switch, and if you have both a momentary normally-open and a normally-closed switch available then the latching circuit on this page would do the job.

A good selection of basic relay circuits on this page, including two latching circuits using a single momentary switch. The price you pay for using the one switch though is that it requires multiple relays - four in total in the first circuit plus two diodes, or the second circuit dispenses with the diodes but requires a fifth relay. That's all a bit clumsy and bulky though and would need careful construction if it was to be reliable in operation.

There are latching relays available but I think they require the use of two switches. There will be other solutions too but they're likely to require the addition of a few components - resistors, capacitors, diodes, maybe a transistor or two for coil switching purposes, and I don't know if you would want to go to that level of complexity. Somewhere in the house I have a textbook containing nothing but relay circuits - delayed-on, delayed-off, etc., and that's sure to include a latching circuit or two but I can't find it right now, probably because I haven't used a relay in a circuit in over a decade. A Google search containing the words latching relay circuit would probably lead you to some other solutions.