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-   -   One time Pulse with a 555 Timer (http://www.physicsforums.com/showthread.php?t=145344)

scottietohottie Nov25-06 05:41 PM

One time Pulse with a 555 Timer
 
1 Attachment(s)
Hello

I currerntly have this circuit -

http://www.physicsforums.com/attachm...1&d=1164497449
circuit1.jpg

I am trying to keep it as simple as possible. I have scoured loads of site etc, an have even found the circuit I want, or should I say it is described as the one I want.
:uhh:

I have replaced R with a potentiometer to make the output variable, but the aim is to make this a one time circuit. I want to push a current through the circuit it fire for a variable amount of time (via the potentiometer), then stop even though the trigger has not.

I have been told that this is done with the use of and extra capacitor, resistor, LED and Transistor (used as a not gate) to get this to work. So far all of the layouts I have been given have not worked. Any ideas would be great.
:biggrin:

Thanks
Scott

scottietohottie Nov27-06 03:13 AM

So I am guessing that the answer is is harder than I thought. Darn. Any ideas what could produce a similar action?

berkeman Nov27-06 09:55 AM

Sorry, what exactly is the function that you want to generate? When you push a button, you want a single pulse output, where the width of the pulse is variable with a potentiometer? Is it at each button push, or is there a reset or something needed to get ready for the next fire? You'll need to start with debouncing your switch, of course. Do you know how to do that? What is the range of output pulse widths you want to generate? To what accuracy?

scottietohottie Dec10-06 04:48 PM

Sorry took so long (Computer crashes are gay hum k). I have a constant input and I want to convert it to a single pulse, the length is between 0.25 secs to 10 sec or near as can be. A switch is thrown that gives a constant input which will trigger the circuit to give an output of the same power (12 car battery) for T (where T is time between 0.25 and 10 secs). Had so much fun tring to get the answer to this question.


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