One shot switch that latches open after one pulse?

Thread Starter

Maxwell Lucas

Joined Feb 21, 2018
I’m an occasional electronics tinkerer, and I’m trying to figure out a switch which closes for one momentary pulse, then latches open until a second switch is opened/power removed. I think I’m not quite finding the right terms to search for, or the results are buried by more common configurations.

I’m modifying an alarm clock so that the alarm must be deactivated by a keyed switch. Keys to be stored a distance from the alarm clock. I’d also like to limit it to one push of the snooze button, just to silence the alarm while retrieving the key.

So I have the keyed switch, closed while the alarm is on. Would like to have another momentary switch, closes for a quarter of a second or so then open despite any further button presses until power is removed by the keyed switch.

I’m pretty sure I could do this with a 555 or maybe something even simpler, but not sure exactly how. Found plenty of info on latching a circuit on after a momentary button press, but not about latching off.

Any help would be much appreciated, thanks.


Joined Jan 29, 2010
hi Max,
Welcome to AAC.
The logic you require is a Bi-stable latch , [ also known as a Flip/Flop]
A HEF4013 D Type latch is one example.



Joined Aug 27, 2015
For the momentary switch that only closes once, you need a transistor, a 1,000u electrolytic a few resistors a tactile switch and a 9v battery.
Connect the collector and emitter across the terminals of the snooze. The 1,000u will have charged via a 3M3 and is connected to the base via a 1k resistor. When you push the button the 1,000u gets discharged into the base and will not work again for 10 minutes.