Help with a momentary contact switch

Hi everyone. I'm currently working on a new Instructable, and I've hit a small wall. What I'm looking for is a momentary contact switch that closes for a second, then opens again on its own independently of the actuator -- and I can't quite figure out how to do it.

To clarify, here's the operation:
You lift the receiver (or handset, or whatever you like to call it) on an old telephone, and the buttons -- normally held down by the receiver -- lift up to create the contact so the telephone knows you've answered and the call connects. Well, this phone isn't going to be connected to the telephone network any more, but what I want is for a contact to be closed momentarily when you lift the receiver, and then opens again automatically on its own even if you haven't put the receiver back down.

I also want the same contact to be made when you eventually do put the receiver back down -- so you replace the receiver, a contact is made momentarily, and then opens again on its own, even though the receiver buttons remain down.

I hope that makes sense, and that someone has a bit of advice on how to achieve this. Thanks in advance!

EDIT: Been continuing my research, and found the following: http://www.simprojects.nl/toggle_to_momentary.htm
Can anyone confirm if this will achieve what I'm looking for? Thanks again.

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Goodhart6 years ago
Yes, I have actually used something similar. There are mechanical "mometary switches" (not thinking of the kind you push then release) that make contact but as you push them break the contact, but that would be harder to make last for a full second.
graffitiwriter (author)  Goodhart6 years ago
Well, I say a full second, but that's kind of misleading now I read it back. It's more a case of creating a "quick button press" from a switch that might stay open or closed for extended periods. Do you have any links or details to the mechanical switches you mentioned? Thanks.
The switch I was thinking of, isn't used much any more, and would act similarly to a "keyboard" switch, where there is not "repeating" when pressed, it makes contact then releases immediately. I don't think that is what you are looking for.

Circuits that latch "until a condition is met" or "until a condition changes"  are not difficult to create with a capacitor, a few resistors and a transistor (or maybe a triac).   Or, if it needs to latch, maybe like this one?  
Goodhart,
It may be that the mechanical "push through" switch you mention is exactly what I need. If you push and hold, it makes a momentary contact. Once you release, it makes a momentary contact. Do you have any suggestions for such a switch action? Who to contact?
graffitiwriter (author)  gvanbuskirk6 years ago
What you're describing is exactly what I'm looking for, but so far it would appear they don't exist. I'm planning on testing out the simple circuit that activates a relay momentarily through an electrolytic capacitor whenever the switch is activated (in either direction). I'll report back when I've given it a test.

The downside of the relay approach means I'll now need to power my Instructable, but that's not a particularly big deal.
depending on how much power you have a available or how much is needed, you may be able to accomplish the same effect with two transistors (one NPN one PNP).
It sounds like such a simple (and unusual) mechanical switch does not exist -- although I'm surprised and will not stop looking. An electronic implementation would work, but does require power. Thanks for commenting.
Well, I am trying to conceive of why you'd want a switch to make contact a second time as you release the button?
It seems that most Android phones short the microphone contacts to indicate a headphone cord button press. This makes the corded mic inoperable if used in the familiar PTT format. I want to make an adapter cable that can signal the start and end of speaking w/o a second unnatural button press. Might still be something we can do within the Android programming for the only 4 contacts we can easily access. It is only a game. What fun.
I was thinking, something "could" be rigged/built to accomplish it easily enough (well, fairly easily) but it might be bulky and cumbersome.
DoublePulseSW.bmp
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