by yonghui » Thu Sep 15, 2011 12:55 pm
hello,
i m not interested to read the whole document. but from the 1st few paragraph, i see that the circuit measure the skin resistance. from my guess the touch pad is just as simple as 2 conductive metal plate. the resistance in skin determine the small current through the base of the BJT transistor. this cause slightly larger changes of the current in collector or emitter of the BJT. current fluctuations in emitter cause the voltage across the emitter resistor to change and the IC shud be an opamp?that compare the voltage with standard calibrated reference voltage; then decoded by the ic and displayed by the LED for the voltage level.
if u are measuring physical finger press that cause the stress, then the sensor i recommended can be used.
else if u are measuring skin resistance, the sensor cannot be used.
of course the circuit given in the document still can be used for both case but with some calibration of the resistor value.
regards,
yh
thanks®ards,
yh