How to Design Schematic Circuit of Electroscope.

 An electroscope is an instrument that can be used for detecting the presence

of an electric static charge. We describe here an electronic version of the

traditional electroscopHne that is made with gold foils placed into a glass

jar. This circuit can also be used for "snitfing" high voltage without actually

making contact with dangerous circuitry.

A metal ring, which constitutes the sensor, is simply poked into the electric

field. This operation must be done with caution to avoid contact with the conductors carrying the high voltage.

You can use the device in experiments with high voltage generators (Van de

Graaff accelerator) and in many other applications athome or school.

The circuit is portable, powered from four M cells or a 9V baftery.

Presence of a static charge or a strong field created by high-voltage lines is

indicated by an LED.

The schematic diagram of the Electroscope is shownin Figure l.The circuit

uses four gates of a 4093 lC that work as buffers and inverters, driving the

LED. The high-impedance input of the CMOS integrated circuits results in

high sensivity to detect static charges.

All the components are mounted on a homemade printed-circuit board as

shown in Figure 2.

Sensor X1 is a small bare wire lop. The completedcircuit can be housed into

a small plastic box with the batteries. The LED should be placed in a visible

point of the box.

To use:

Bring a charged source close to the sensor. Apiece of paper or plastic stroked

with a rod of insulating materialwill do. Adjust Pl to get better sensitivity.The

LED will glow according to the electricharge movement.

Parts List - Electroscope

IC1 - 40938 CMOS Integrated Circuit

LED - Common red, yellow or green LED

X1 - Sensor - see text

P1 - 1,000,000 ohm potentiometer

R1 - 22,000,000 ohm, 114W,5% resistor

R2 - 100,000 ohms, 114W,5% resistor

R3 - 1,000 ohms, 114W,5% resistor

S1 - SPST slide or toggle switch

81 - 6V or 9V - four AA cells or 9V battery