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[SOLVED] Pulsed output from switch open and switch close

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maxxsinner

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Hope someone with a little more experience can help me with this one. :-D

I am looking to design a circuit that has the following -

  • On the open of a door, a pulse output switches a relay for a few microseconds
  • On the close of the same door, a pulse output switches the same relay for a few microseconds


I was thinking that a microswitch connected to a couple of 555 timers with the input trigger to one through an inverter would do it but wondering if I am overcomplicating it?

Appreciate any feedback.
 

If you use a change over microswitch and wire both the the NO and NC contacts together, then the switch will only be open during the change over time of the contacts, it'll be small though in the millisecond range rather then microseconds.
Frank
 

Thanks Chuckey. I will give that a go.
 

The fastest you will get a relay switching is a few milliseconds - if you drive it strongly with a high current. More likely you might manage 5 to 10 ms.

If using the shorted-microswitch approach (nice idea Chuckey) then you might still want the 555's as pulse stretchers - otherwise the relay is never likely to get enough time to switch from the short pulse from the microswitch.

What are you trying to achieve with this? There might be a better way.
 

Thanks for the feedback FoxyRick.

What are you trying to achieve with this? There might be a better way.

Well short story long is that there is a bunch of us making full size virtual pinball machines. We are trying to emulate a real cabinet as much as possible and one of the things that I personally would like to do is when the coin door is opened on the front of the pinball cabinet, it sends a pulse to the keyboard encoder to simulate a key press, this in turn activates the rom to react as a real pinball cabinet would and go into control menus etc.

Then when the door is closed again, it needs to simulate the same keypress to be able to tell the rom that the door is shut and resume normal operations.

Complete overkill on my behalf, but a firm believer at start at overkill and work your way back :-D

Any suggetions other than a 555 I am certainly open to. Love having a reason to break out the breadboard.
 

Re: Pulsed output from switch open and switch close - [Solved]

I can confirm this works perfectly gents. A 10kΩ resistor in series with a 10µF capacitor on the trigger with both the NC and NO brigded (talk about thinking outside the box there Chuckey :-D) and the 555 fires one shot and ignores the button being held in. On release of the button it fires again for the preset time.

Your help is very much appreciated. Thanks!
 

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