Hi Roman,
I just pulled out some of my older membrane keypads from 1988 and 1992.
These have been 'beat to death' in retail industry distribution centers =
5
to 6 days per week, hundreds of presses per shift, 2 to 3 shifts per =
day.
On the keys that still work, the resistance is between 10 and 20 ohms.  =
The
manufacturers spec is <100 ohms guaranteed.  BTW, these are the all =
mylar
keypads, conductive paint traces and metal backplate.  If I have some =
time
this afternoon, I'll pull out some of my REALLY abused keepers and do =
some
tests on them.  Hope this helps your confidence level.

Bill


At 12:25 AM 06/01/2002 +1000, you wrote:
>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 =
process
>> 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 =
over
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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