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!

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    \$\begingroup\$ 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? \$\endgroup\$ – Transistor Sep 3 '18 at 9:23
  • \$\begingroup\$ 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. \$\endgroup\$ – Garet Sep 3 '18 at 11:04
  • \$\begingroup\$ 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. \$\endgroup\$ – Garet Sep 3 '18 at 11:06

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

enter image description here

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.

  • \$\begingroup\$ It was really simple. Thank you! The schmitt trigger gate is to avoid bouncing problems, right? \$\endgroup\$ – Garet Sep 4 '18 at 9:06
  • \$\begingroup\$ @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. \$\endgroup\$ – Andy aka Sep 4 '18 at 11:04
  • \$\begingroup\$ 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 ? \$\endgroup\$ – Marc Brillault Mar 26 '20 at 1:08
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    \$\begingroup\$ Maybe you are looking in the wrong store and need to buy on line from RS, Farnell, Digikey or Mouser. \$\endgroup\$ – Andy aka Mar 26 '20 at 8:09
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    \$\begingroup\$ It's the same thing. \$\endgroup\$ – Andy aka Mar 26 '20 at 14:02

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