Re: [uCsimm] SIMM hardware question

From: daniel haensse (daniel.haensse@fhk.usz.ch)
Date: Wed Feb 21 2001 - 09:43:22 EST


Am Mit, 21 Feb 2001 schrieben Sie:
> On 2001.02.20 16:38:27 +0000 Jean-Marie Bussat wrote:
> >
> > > I am working on a project in which I need to process inputs from a couple
> > > relays (i.e. the relay is either open or closed by an external source). Is
> > > it acceptable to simply use the relay to feed +3.3V from the uCgardener to
> > > one of the PDx pins, or does it need 5V, or is something else needed?
> >
> >
> > But, if you plan to use them in an interrupt driven system (i.e. you
> > will look for an edge/change of the contact state), you will need an
> > "anti-ringging" circuit since when a relay contact closes or opens,
> > it doesn't not do that in a very "clean" way. You may have successive
> > closing/opening of the contact before it reach its mechanical stable
> > state. This may generate spurious interrupts that may confuse your
> > program.
> > "anti-ringging" circuits can be as simple as a R/C network or it
> > can be made using a monostable. It also exists some integrated
> > circuits that are doing this job (I dont remember any reference...).
>
> Could you not just wait for a few ms (maybe quite a few) and then test
> the input to make sure it's valid?
yes, detect the edge, wait some time until the mechanics is debounces
and then take a sample (just don't wait to long, maybe you can take a second
sample some us later and compare it to the first). Works perfect without any
external components.

Dani
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