momentary switch help

[markland556]

ok, so i want to set up a front pannel and i really rather would use momentary switches to turn on and off my leds and cold cathodes. Is this possible?? like you press it and it activates a relay, idk im kinda a noob to relays, but i know my share of electronics.

 

[Herulach]

essentially what youd need is 2 switches. And set up either a transistor or resistor to be bistable, id say a transistor, cos it wouldnt be all clicky then. basically, using a transistor, one switch closes the circuit to the base. Then you tap the emitter wire back round to the base as well, put your second switch on this wire, that way, push the first switch, its on, the second will make it go off.

 

[markland556]

well i kinda wanna have onr switch turn them on and off.

 

[The Brain]

It is possible to do what you want with a small digital logic circuit. What you need is a J-K flipflop.
Basically a J-K flip flop can be wired up such that its output will toggle everytime a pulse is provided to its clock pin.

I.e. One pulse -> Output goes high
Another pulse -> Output goes low

To properly use this circuit you would need a switch debouncer circuit (a capacitor and a resistor), and a power transistor.

 

[markland556]

well how about a circuit diagram

 

[mattg2k4]

Google will help you easily find many basic circuits such as that, and datasheets frequently have example circuits on them as well.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm has a couple of circuits that you should find useful.

 

[SarverSystems]

It doesn't HAVE to be a momentary switch, does it? Why not use a pushbutton?

I assume you want to stay away from the usual bat-handle, toggle switches that EVERYONE uses. Why not get a push-on push-off switch?

 

[aL Mac]

flip flop is the way to do it.

 

[markland556]

i want to use a momentary switch because it would be......... better.......

 

[cpemma]

A simple flip-flop method here.

 

[markland556]

that should work perfect, but i think the output is 12v, can i just supply +5v to the circuit or should i just take it from 12v to 5v with a resistor??

 

[cpemma]

5V may not be enough for that particular mosfet, but no problem if you use an NPN transistor like the 2N2222A (800mA max). You have 5V CCFL?

 

[markland556]

well if i splice the the +5v line then i can use the transistor.

 

[aL Mac]

that should work perfect, but i think the output is 12v, can i just supply +5v to the circuit or should i just take it from 12v to 5v with a resistor??

are you talking about the supply or output?! Most CCFL's are 12V that I know of but if you had one that was 5 V or something else you could just use a resistor as long as there wasn't too much current going through it. P = R i^2 or P = V^2 / R or P = V * i make sure that it's power P is less than what it is rated for or equal.

 

[markland556]

ok, nv it is 12v i just always make that mistake because they use the dam red wire going back. but anyway, i cause use that exact circuit if i just get a transistor that will allow 12v through when it gets that 12v signal. or should i just run the CC off the circuit directly, because i will also be hooking up some 5v leds and how would i do that, proably use a transistor.

 

[cpemma]

... i will also be hooking up some 5v leds and how would i do that, proably use a transistor.

If you hook "5V" LEDs directly to the 5V line I don't think they'll last more than a day before fading. 5V is, at best, the absolute maximum voltage they'll take; at worst it's the LEDs peak inverse voltage misquoted on some seller's page. Blue and white LED chemistry gives around 3.5V drop across the diode junction. So use a series resistor on either 5V or 12V psu lines. A resistor calculator here.

I don't understand the other question, there already is a transistor switch in the circuit.

 

[NleahciM]

It doesn't HAVE to be a momentary switch, does it? Why not use a pushbutton?

I assume you want to stay away from the usual bat-handle, toggle switches that EVERYONE uses. Why not get a push-on push-off switch?

Exactly. I don't think the OP realizes that bushbuttons can look and feel identical to a momentary switch.