I built very sensitive static detectors for under a dollar and used
them to detect the Earth's field, power lines and a sweater ten feet
away.
These VN10KM FET based toys were sensitive to most kinds of plastic and
lasted for more than ten years on the original AA power cells. The
circuit
consists of a FET with a 30 ohm limiting resistor and a red light
emitting
diode, connected to a 3 volt battery. The gate is left floating but can
be influenced through a very high resistance made with a thick pencil
line
on a paper. My scrap of paper was one inch long and held with paper
clips
for terminals. The free terminal was centered across the battery with a
potentiometer. If everything is done correctly the LED will be dimly
lit.
A negative object will make it go out and a positive object will make
it
brighter.
Several hundred volts can be obtained in dry weather using a comb in hair. Since this is too much effort for too much voltage a plastic pen is substituted or a plastic bag is rubbed with a hand. The resulting device will easily control the instrument for a few minutes.
Wiggle the pen near the static sensor and watch the LED. Once the
kids
see this it they will want one.
Last edit September 2004.