Button/switch debouncing

[xnihilo]

Hi guys,

I was wondering what delay I should use in debouncing a switch.
I'm using 100ms debouncing, but that seems like overkill.

Would 1ms be enough? Or would 10ms be enough.
I guess it depends on the switch/button I use but I have no mean of knowing the bouncing of a given switch.

Thanks for any answer.

Regards

[Darrel Taylor]

Some interesting (although Long) reading.

A Guide to Debouncing
http://www.ganssle.com/debouncing.pdf

Pretend it's a Playboy magazine, and just look at the pictures.
<br>

[xnihilo]

Yes, I've just finished to read that. Interesting. 10ms should be enough.

Is this piece of code right? (a lever microswitch connects ground and RA0 of a PIC16F684 (input with WPU enabled for this pin)

start:

while trigger = 1
pause 10
wend

Thanks

[Darrel Taylor]

NO. It'll take more than that.

You need to test it again after the pause to make sure it's the same, and you should debounce both edges.
Or a single pulse of any length, could re-trigger another keypress.
<br>

[Rob]

Hi xnihilo,

in the past I have used something like:

Start:

If Trigger = Pressed then
For CountByte = 0 to 9
Pause 1
If Trigger = NotPressed then Start
Next CountByte
' Trigger is still pressed so do code here........
Endif

End

This approach works well for me, checking the button 10 times at 1ms intervals, and will give you a starting point.

Of course, there is always the PBP Button command...

Hope this helps

Rob

[Melanie]

I think in the simplest form it's overkill...

Look, you're not trying to ignore static from a localised lightning strike, just trying to detect that a Button has been pressed... so simply...

	If UserButton=0 then
		Pause 10
		Goto ButtonPressed
		endif

The IF statement checks if your Button has been pressed... The PAUSE simply ensures that you don't check for the press again within a set time period (which should be longer than your worst-case anticipated debounce time). Now, for user entry, I like to have a 100mS pause, this gives a nice 10cps repitition rate if you keep your finger on the button. If you only want ONE keypress, then simply check that it's been released first before doing anything else...

	While UserButton=0:Wend

If you have a scenario where you have problematic static, then check for a Button Press once, pause a while, and check it's still pressed some time later. Static is momentary, so you will eradicate an awful lot of false triggering with something like...

	If UserButton=0 then
		Pause 10
		If UserButton=0 then Goto ButtonPressed
		endif

[Patrick Pending]

Hi xnihilo,

Of course, there is always the PBP Button command...

Rob

I have noticed quite a few Picbasic Pro programs which use a button de-bounce routine instead of the button command. If it's not a silly question, when and where should I not use the Button command?

Thanks,