The design of the circuit established the usage of Field Effect Transistors (FET) , as a precise detector of static electricity. It detects the invisible fields of voltage encircling every item subjected to electricity by identifying the occurrence of negative ions.
Static elctricity refers to the accumulation of electrical charges on the exterior of an item or material. As objects are rubbed together (like wool on plastic and comb on hair) or pulled apart, static electricity is formed triggering positive (+) charges to gather on the object and negative (-) charges on the external. It experiences the triboelectric effect wherein the process causes electrons to be pulled from the exterior of one object and relocates to the exterior of the other object. The effect of static electricity could result to flickers, shocks or objects sticking together. It was termed as static for the reason that there is no current flowing, unlike the direct current (DC) and alternating current (AC) electricity.
The circuit creates a static field sensor with the use of 2N3819 field effect transistor because of its low impedance and sensitivity to voltage variation on its gate terminals. In the diagram, the gate terminal is kept open where a probe, made of naked copper wire, is connected. Since there is no external source applied, the signal will show a charge when the gate terminal reacts to a sudden change in voltage.
The efficient gate impedance will be reduced if the circuit is made on veroboard or PCB. The probe should never be in contact directly and properly insulated in a plastic sleeve. To avoid bending the needle of a multimeter, it will be better to set it to full scale deflection of 1mA or 250uA for greater sensitivity. The multimeter will be used to measure the voltage between FET drain and the preset resistor.
A FET is a type of transistor that produces current in comparison to the input voltage. It uses a small amount of direct current to control a larger amount of output current. FET 2N3819 is a high-quality N-channel JFET, that is low-cost but offers excellent implementation at mid-to-high frequencies. It provides low noise and leakage and assures high gain at 100MHz.
The circuit works like an eletroscope which detects static electricity by applying slim or plactive sleeves, that will separate when charged. This is the most common static electricity detector. Another method is electronic amplification of induced charges. The circuit can be tested by placing it 5 feet far from the TV. The needle of the meter will soar to full scale and then drop down again.