Author Topic: Momentary Pushbutton that releases even if the user doesn't let go  (Read 589 times)

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Offline AsellithTopic starter

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I need a push button that can release even if the user doesn't let go. An actual switch would be great. The other option I am working on is trying to make a circuit that does that. Any help would be great.
Jonathan Bowen
CorSec Engineering
www.corseceng.com

Offline mstacho

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Re: Momentary Pushbutton that releases even if the user doesn't let go
« Reply #1 on: August 03, 2011, 11:36:35 AM »
So you need the user to press the button, the system transitions into some other state for a set time, and then quickly transitions right back even if the user didn't release the button, right?  is that not just a monostable multivibrator? http://en.wikipedia.org/wiki/Multivibrator

Does that do what you're talking about?

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline AsellithTopic starter

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Re: Momentary Pushbutton that releases even if the user doesn't let go
« Reply #2 on: August 03, 2011, 11:45:17 AM »
Yes I've been looking at that. I really wish I could find a physical switch that did this but I guess I'll have to work out the schematics for it and just use a 555 or something.
Jonathan Bowen
CorSec Engineering
www.corseceng.com

Offline corrado33

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Re: Momentary Pushbutton that releases even if the user doesn't let go
« Reply #3 on: August 03, 2011, 02:26:43 PM »
You wanted a physical pushbutton switch that would force itself back up after a certain amount of time to become "unpushed"? 

Offline Soeren

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Re: Momentary Pushbutton that releases even if the user doesn't let go
« Reply #4 on: August 03, 2011, 09:29:34 PM »
Hi,

A simple R1-C-R2 circuit should do. Button is isolated from the input via a small cap and a pull-up resistor at each side of the cap discharges it when the button is released. When pressed, the other side of the cap will go low for whatever RC time selected (R2) and then rise. If the input is sensitive, add a protective diode (cathode to positive side, anode to input).

If you need the pulse to go high and rest low, just use pull-downs instead and move the eventual diode so cathode goes to input and anode goes to 0V.
Regards,
Søren

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