Playing With High Voltage Static Electricity

Although static electricity may amount to thousands of volts it is generally safe because the circuit impedance is so large that high currents rarely develop, or are limited to very short times. A person can easily and safely carry thirty thousand volts. This voltage is commonly produced by a rug in winter.

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.