I suspect it could relate to operation of the contact between conductive to=
p wiper=20
contact and lower resistive element... similar to minimum "wetting current"=
 required=20
for switches and relays to keep contacts "clean", without meeting the minim=
um spec=20
it might work for a while but with reduced lifetime (contact resistance inc=
reases to=20
the point of being un-usable). As 3.3V is so common it would be worth askin=
g the=20
manufacturer specifically, there may be a trick such as adding capacitance =
to the=20
wiper to increase wetting current. On the other hand I could be completely =
going=20
down a wrong track here in which my comments are worthless~!

On 10 May 2011 at 18:58, Sean Breheny wrote:

> Hi all,
>=20
> A colleague of mine is looking at using a membrane strip potentiometer
> as a touch sensor. This is a three-terminal device, just like a
> typical pot, except that the wiper is only connected when pressure is
> applied. In effect, the wiper is actually whatever point or points of
> contact are made between the top foil layer and the bottom resistive
> layer.
>=20
> We were both puzzled to discover that the datasheet for this part
> lists both a max and a MIN voltage. Max voltage is obvious for thermal
> reasons. However, we are not sure why a minimum voltage is listed.
> They list their standard product as rated from 5V to 30V and then they
> state that custom products can be made with ratings ranging from 1V to
> 60V. This seems to indicate that the 5V lower spec is not simply a
> typical value listed for convenience but that there would really be
> some undesirable condition to using a lower voltage.
>=20
> My colleague would like to run this at 3.3V since that is the system
> voltage in his device. Does anyone here have any idea why there would
> be a minimum voltage spec and what the impact of operating this device
> at 3.3V (when 5V is the minimum rating) would be? The only idea I was
> able to come up with is that perhaps there is a certain amount of
> voltage noise present due to operation of the part and that 5V is the
> lowest voltage at which the accuracy specs would not be affected by
> the ratio of the supply voltage to the voltage noise.
>=20
> Sean
> --=20
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> http://mailman.mit.edu/mailman/listinfo/piclist
>=20

--=20
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


--=20
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View/change your membership options at
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