Alexandre Guimar=E3es wrote:
>=20
> Hi, Roman
>=20
> > plated contacts (basically 0 ohms) but i'm concerned
> > that if I go into production the commercial membrane
> > keypad might be a little high for contact ohms, or
> > worse still be ok when sold, but start failing as
> > the carbonised contacts wear and their resistance
> > slowly increases, which I have seen when repairing
> > remote controls etc.
> >
> > Wasn't there someone on the list that works for a
> > keypad manufacturer? Hoping for advice. :o)
> > -Roman
>=20
>     You cannot count on the resistance not varying with time... Most
> membrane manufacturers use silver ink to make the contacts and the proc=
ess
> leads to big variations in resistance. I have some inside information
> because I have made many developments for a keypad manufacturer. How
> critical is the resistance variation ? The contacts should never go ove=
r 100
> ohms.


Thanks Alexandre, that is handy info. The design
will tolerate 100 ohms per contact or so, but i'm
still nervous about contact change in resistance
over time. Would be nice if someone could say
"yes definitely about 100 ohms new, then increasing
to 300 ohms after 10,000 presses etc". :o)
-Roman

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