Hi Brent, Thanks for the reply. Wetting current was my first thought, but I ruled it out because the minimum voltage spec is NOT between the wiper and the resistive element, but across the resistive element, so the minimum voltage spec would not guarantee any current flow through the contacts which make and break. Sean On Tue, May 10, 2011 at 7:21 PM, Brent Brown wro= te: > I suspect it could relate to operation of the contact between conductive = top wiper > contact and lower resistive element... similar to minimum "wetting curren= t" required > for switches and relays to keep contacts "clean", without meeting the min= imum spec > it might work for a while but with reduced lifetime (contact resistance i= ncreases to > the point of being un-usable). As 3.3V is so common it would be worth ask= ing the > manufacturer specifically, there may be a trick such as adding capacitanc= e to the > wiper to increase wetting current. On the other hand I could be completel= y going > down a wrong track here in which my comments are worthless~! > > On 10 May 2011 at 18:58, Sean Breheny wrote: > >> Hi all, >> >> 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. >> >> 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. >> >> 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. >> >> Sean >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > -- > 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: =A0brent.brown@clear.net.nz > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .