Touch switch circuit - has single LC resonant circuit and differential amplifier

摘要

This touch switch circuit is less critical towards component tolerance and environmental variations by having only a single LC-resonant circuit with a high value coupling resistor to the switch. A differential amplifier is provided to form an oscillator. The oscillator comprises a differential amplifier (2) and a single LC-resonant circuit (14) and is coupled to the touch switch (22) via a resistor of 100-100 K ohms and a d.c. blocking capacitor (20). An adjustable shunt resistor (34) provides variable sensitivity.