1 reply to this topic

[RARusk]

I am looking for a specific type of momentary switch. In a regular momentary switch the contacts stay closed as long as you hold down the switch.

What I am looking for is a momentary switch where the contacts re-open (after a short time - less than a second) even if you are still holding down the switch. I don't know what the name of this type of switch or the specific property is.

I am trying to finish off an old project and this is the last major obstacle to complete it.

[Stephen Moss]

I assume that once they have re-opened you want the contacts to stay open with the switch still held down. In 20 years of working with circuits and repairing equipment I have never heard of a switch with contacts that would re-open by themselves, they may exist but I am doubtful that is the case. I would suggest you look at a 555 timer wired as a monstable, use the switch as the trigger and the output state of the 555 changes for a time determined by the Reistance and Capacitance values used before returning to its default state where it will stay until re-triggered.

I hate 555 timers as in my experiance they either work first time or are complete bastards to get going, plus the defaut output is High (i.e. +5V) so you many need to invert it depending on your application, personally I would program a PIC instead as you can set the default state to whatever you want (+5V or 0V) and they don't need external components if you use one with an internal RC clock. Something like a 12F683 would do provided you don't want the output to change back (contacts re-opening) in less than 10uS (a nice, safe, round value).

Edited by Stephen Moss, Wed Aug 31, 2011 2:03 AM.