Touch Switch with MPF102 JFET

Posted on Apr 22, 2012

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
Click here to download the full size of the above Circuit.

Q2 is held cut off since Q1 normally is conducting.

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