QT113-D Touch Sensor Help

Guido

Has anyone tried the QT113-D Touch Sensor sold by Parallax. I have been playing around with it and I can not gain any or much sensitivity. Using the max size cap, .01 and a touch field about the size of a quarter, I can only trip it by touching it using a 1/16" of Glass. Any more distance and I can not seem to get it to work.I have also wired the Gain (Pin 5 ) to +5vdc. Any Help would be appreciated.
Thank You
Guido
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Chris Savage

Guido,

·· Have you followed some of the guidelines in the Datasheet for increasing the sensitivity?· Also note that some materials work better than others.· Glass is typically an insulator (And an extremely good one) so it won't work as well as some other materials.· The datasheet recommends using a bigger electrode, or reducing panel thickness or altering composition for some improvements.


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Chris Savage
Parallax Tech Support
csavage@parallax.com


Post Edited (Chris Savage (Parallax)) : 9/7/2005 2:46:02 PM GMT

Paul Baker

The touch sensor operates off of a capacitive effect, where the electrode is one plate of the capacitor and your finger or metal object forms the second plate. Capacitor values are determined by the suface area of each plate, the dielectric material and dielectric thickness. The dielectric is the insulation material between the two plates. Changing any of these parameters effects the capacitance and the ability of the sensor to detect a change. There are many types of glass in existance and each has thier own dielectric constant, for instance many impurity laced glasses have a higher dielectric constant than pure amorphous silicon dioxide (silica glass=3.8). Also many natural materials produce a higher dielectric constant, quartz (4.2) and mica (7.0) are excellent examples. Plastics such as acrylic (2.8-4) and lucite (2.5-2.8) and polyester have dielectric constants on par with glass but can be made to much thinner thicknesses without serious risk of breaking as in glass, so the capacitance is raised through alteration of a different parameter, Even polyvinylidene chloride (Saran Wrap) can achieve excellect dielectric properties because of it's very low thickness.

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·1+1=10

Post Edited (Paul Baker) : 9/7/2005 3:50:26 PM GMT