For a change, this simple touch-sensitive switch does not operate by detecting the resistance of the skin between two points or measuring the change in capacitance, but it reacts to heat instead. The negative temperature coefficient of a silicon diode is utilized for this purpose.
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Diodes are normally used to rectify signals, but they are also suitable for other applications. Here we use a property which is normally considered to be undesirable, namely that an ordinary silicon diode has a negative temperature coefficient of about –2 mV/°C.