I have fond memories of the little "lie detector" circuit I made
back in high school.  A little cmos 4009 hex inverter configured
with two inverters as an oscillator that used a nice PCB pattern
to include your finger resistance to help determine frequency,
and the remaining 4 inverters in parallel as an LED driver.

But it only worked SOMETIMES, depending on how you squeezed it.
Turns out that the osc and the LED driver weren't actually
CONNECTED to one another.  If your fingers were in the right
places on the BACK pcb, they conducted enough signal to make
CMOS happy.  Otherwise; not.  An educational experience!

BillW

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