Touch Switch with MPF102 JFET

  
When the touch plate is contacted by a large object (human body, etc.), stray 60-?? pickup is rectified by D1 and D2, and produces a negative voltage across R2-C2 and the gate of Q 1. Q1 cuts off, causes Q2 to conduct, and the output goes low.
Touch Switch with MPF102 JFET - schematic

Q2 is held cut off since Q1 normally is conducting.




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