Need help building circuit

[chopperdog]

Hello everyone.
New here.
I am trying to build what I think is a farily basic circuit, but I don't know how to do it.
I need a switch that will close for a very short time, then reopen. For an example, close for .25 seconds, then open for .75 seconds. I would like for this to happen, and continually repeat, and all of this only when a push switch is selected.
This is a 12 volt circuit.
The purpose is to momentarily stumble an engine.

Any help would be greatly appreciated.

Thanks,
Chopperdog

 

[bychon]

This is normally done with a chip called 555 or LM555, NE555, SE555. Anyway, you make an oscilator with this chip and the result is a square kind of wave which changes at the rate and times you told it to with 2 resistors and a capacitor. That will be used to control something more powerful, like a relay.

Here's a "data sheet". It tells all about the timer chip.

 

[Dragon Tamer]

This forum also has a 555 calculator built into it, so you can calculate what values you need to use to get the desired frequency. I would recomend modifying the duty cycle of the output for your specific circuit.

 

[chopperdog]

Thanks for the replies.
I will try to familiarize myself with the 555 chips.

 

[chopperdog]

Could a 555 chip handle the 12 volts of a car battery, or would that result in too much amperage?
I read on a site that the 555 chip can handle up to 15 volts.

 

[Hero999]

Ye, an NE555N can be connected to a car battery, the only thing you need to add is a fuse to prevent the battery blowing up if there's a short circuit.

 

[chopperdog]

Thanks again for the help.
Is it possible this is an existing circuit design? I have seen 555 designs, but haven't found this yet.

The idea is to close a switch for a very short period of time, .25 seconds or so, and then open the switch for about 1 second, and repeat this cycle as long as a momentary switch is held down.
This whole idea is to simply stumble the ignition of a car motor.
I understand the 555n should work, but I'm not totally sure how I would wire in the 12 volts, ground etc.
Also, I am assuming that I would need 2 incoming 12 volt positive lines. 1 for the power to the circuit, the other being the supply that is shorted out when the switch is closed.
Any help is greatly appreciated.

Thanks,

Chopperdog

 

[MikeMl]

If you were going to do this manually with a normally-closed switch, where would you wire it? Would it go between +12V (IGN Switch) and the coil through a ballast resistor? Opening the normally-closed switch would effectively momentarily turn off the ignition? I think you want the switch to Open a circuit, not Short something.