Switch debouncing

Abstract Dissonance · 2005-12-28T01:27:30+00:00

For one of my projects I decided to use a momentary switch(where its held on as long as you push it in and when you release it will disconnect... I think its called momentary switch). The switch basically selects presets and I will have a couple of them. The idea is like the buttons on a blender where you press one and it mechanically turns off all the others. I'm trying to do the same thing digitally. i.e., if I press button A it will turn off all the others(only one will be on ofcourse). I do this by basicaly using toggle FF's.The main issue I have, I think, is the switch debouncing part of it. I've look on some web sites and they basicaly give a few methods such as a simple filter circuit(which I think won't work on mine because of the switch type) and an monostable vibrator. Anways, I feel that I can do this with just some resistors and capactiors. By looking at the idea for a monoastable vibrator where they used a capacitor to "slow the change" I figure I can sorta do the same.Basicaly the way I see it is that when the switch bounces it will discharge a capacitor... the more bouncing the more discharge. By setting the capacitor to slowly charge but discharge quickly when the switch is pressed the voltage across the capacitor is 0... any bouncing will discharge the capacitor as it slowly charges. By using a schmitt trigger then I can get a high only after the capacitor has charged enough. By setting the time constant one should be able to get rid of the bouncing(its effect is to length the time it takes to charge).The circuit is ---- Schmitt Trigger - Out |V --- R1 --+-- Switch --- R2 --- GND | --- C1 -- GNDWhat I'm wondering is if this is an effective circuit(i.e., if its practical). I can simulate it and it seems like it would work but I have no idea if it will work in the real world(and I have no components to test it but will order some soon after I get a general idea what I need).I figure the only problem is that if...

Dec 28, 2005 21 Replies

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Abstract Dissonance 20 years ago

Ok, I'll keep that in mind. I'm not to familiary with all the different types of switches and stuff and not sure which is the best method. I actually might end up switching to a rotary style switch so I can save some space but get more poles(?).

Thanks, AD

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Abstract Dissonance 20 years ago

yeah. I was using low values of R2. I think I put it there to limit the current and to actually see the thing charge.

I'm not familiar with that.

heh. Ok, I'll try it and see what happens. So basicaly you are making a filter and a using a diode as a sort of voltage limiter(so basicaly the bouncing will have to overcome the diode but since you put a cap and resistor there to reduce the voltage and filter it it will not have enough to do it?).

Thanks again, AD

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