Herbert Graf <mailinglist2@FARCITE.NET> wrote:
> Stave wrote:
> > Ah ! One of my pet peeves.
> > If you didn't do it backwards, there wouldn't be a delay. Why are you
> > waiting for the switch to finish bouncing ? Start acting as soon as you
> > detect the first closure and then ignore any activity for the worst case
> > bounce time.
> > This has been taught wrong since Adam was a boy and nobody has
> > thought about it since.
>
> It hasn't been taught "wrong". Power supply glitches (or any other form of
> noise) can cause a button to "appear" to be pressed, your technique would
> trigger on such a "button press". It's worse for a device to respond to a
> false button press then to not respond at all in many cases. Guess you
> didn't think about that.

No, Steve has it right. Leading edge switching makes a huge difference in
customer perception, even at the 50 - 100 ms level.

If you have so much crap floating about in your system that a power supply
transient can look like a bouncing switch, then you've got worse problems
than user perception. You need to deal with that separately (e.g., filters,
hysteresis, and in extreme cases, double-throw switches), and not rely on
the switch debounce function to hide it.

-- Dave Tweed

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