Convert a toggle switch into a momentary response

Question

I'm working on a project and I need to use a toggle switch to control a device that expects a momentary signal.

What I want is send a momentary pulse when turning it on and off. Ie: swith off to on: positive pulse, switch on to off: positive pulse again.

I've got do this with a small arduino-like board but I'm looking for a pure hardware alternative.

My knowledge of electronics are quite small. I thought about using an inverter (NOT gate) to detect both latches (low and high) in the toggle switch plus a few more components, but I'm not sure how to design it.

Any ideas?

Thank you!

Doing this in hardware makes no sense if the switch is wired to the micro-controller input as you can detect a change of state in software. What is the problem with the software approach? — Transistor, Sep 03 '18 at 09:23
The switch is not wired to the micro-controller. I did a test with a micro-controller to see if I was capable of solve it. — Garet, Sep 03 '18 at 11:04
Actually, there are two separate system that I want to combine. A controller with some switches plus other features and a machine that expects momentary signals. I want to add a small box between both system to convert the latch signal of the toggle switches to a momentary response without modify any of the two systems. — Garet, Sep 03 '18 at 11:06

score 3 · Answer 1 · answered Sep 03 '18 at 11:58

3

You could use a schmitt trigger EXOR gate like this: -

Every time the input waveform changes state you get a positive pulse at the output and the duration of that pulse is determined by the RC time constant.

answered Sep 03 '18 at 11:58

Andy aka

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It was really simple. Thank you! The schmitt trigger gate is to avoid bouncing problems, right? – Garet Sep 04 '18 at 09:06
@Garet No, the schmitt trigger is fundamental in turning a rising or falling edge at the input into a positive pulse whose width is determined by R1 and C1. – Andy aka Sep 04 '18 at 11:04
Hi, I'm looking for the very same thing, but I cannot find it in any store (i'm guessing there are already premade chips for that ?) Are ther other names to find something like this ? – Marc Brillault Mar 26 '20 at 01:08
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Maybe you are looking in the wrong store and need to buy on line from RS, Farnell, Digikey or Mouser. – Andy aka Mar 26 '20 at 08:09
Is EXOR similar to XOR ? Or are these two different things ? – Marc Brillault Mar 26 '20 at 13:34
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It's the same thing. – Andy aka Mar 26 '20 at 14:02
Oh, thanks, that's mainly why I couldn't find it. And many thanks for the shops suggestion ! – Marc Brillault Mar 26 '20 at 14:10

Convert a toggle switch into a momentary response

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