Long wire capacitive touch sensor switch
Est wrote 10/22/2015 at 00:24 • 2 pointsI needed to connect a touch pad to the touch sensor IC with a wire long about 15 cm. Both the wire and the pad are sensible to the touch and this may be annoying as the user can activate the touch switch placing his hand near the wire instead to the pad. To make the wire not sensible to the touch i tried to shield the wire with a audio coaxial cable used for microphones but this decreased the sensitivity of the capacitive sensor and it was not able anymore to be activated trough the thick plastic above the sensing pad. I guessed that the capacitance of the cable decreased the sensitivity of the IC, so i made by myself a coaxial cable with a thick insulation between the shield and the internal wire and it did work.
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Another thing you can do is this: instead of having the shield be ground, drive it with a buffered version of the sensing signal. Because there is no voltage difference between the sensing node and the shield, the cable's capacitance that used to decrease your sensitivity will instead be ignored. Look up "driven shield" for more details.
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Thank you. Good tip, i will not try it this time tough, as i had already done the PCB.
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Nicely done!
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