Small and convenient non-contact electrometer

The compact non-contact tester has the advantages of simple circuit, reliable performance, and easy use. It can detect whether the power wire is charged outside the insulator of the power wire and detect the fault point of the hidden wire. It is essentially a highly sensitive AC amplifier.

The time base oscillator 555 forms a multivibrator, and its circuit schematic is shown in the figure below. The field effect tube V in the figure is usually in a zero bias state, and the resistance between its drain and source is small. The 4th pin of the 555 connected to the drain is at a low level (less than 0.7V), the 555 does not work, and the speaker B does not sound. Once there is an electric field signal at the G pole detection end of the field effect tube V, the resistance value between the D and S poles increases, the 4th pin of the 555 obtains a high potential (greater than 0.7v), the oscillator works, and B makes a "beep" sound.

In order to make the electroscope more compact, E can use 2 mobile phone lithium batteries.

The following figure is the connection diagram of the printed circuit board of the electroscope. After the entire circuit board is soldered, the field effect tube V is soldered. When soldering V, the electric soldering iron should be grounded or unplugged to prevent damage to the field effect tube V. The G pole is soldered to the tip of the electroscope's measuring pen. After soldering, perform the following simple debugging. Turn on the circuit switch S, bring the tip of the V detection pen close to the 220V AC power line of the city power supply, and adjust the potentiometer RP so that the speaker B makes a sound when the whole machine is about 10cm away from the AC power supply.

The electroscope can be made into different shapes according to the needs of the maker, and can also be installed in a radio, with the antenna of the radio as the detection pen tip of the electroscope, and the speaker B can also be omitted, which is more practical.