High voltage alarm circuit

The high-voltage alarm has high sensitivity and can alarm 2m away from the 10kV high-voltage charged body or 0.3m away from the low-voltage mains (AC 220v). The device has
few components, a simple circuit, is easy to make, is small, and is easy to use.
    The circuit principle of the alarm is shown in Figure 13120. Field effect transistor
VT1 is a field effect device. When its gate is close to the electric field,
the gate bias is generated due to the induction of the electric field. The on-resistance between the drain and the source will
increase sharply, the corresponding input terminal of Dl is at high potential, and the oscillator composed of Dl and D2
starts to vibrate, generating an audio signal of about 1kHz. This signal is amplified by VT2
, and the input speaker emits an alarm sound. .
    Dl and D2 use two sets of four-input NAND gates 74HC20 (74LS20).
For the rest of the components, please refer to the model numbers or parameters shown in the figure for selection.
    The whole machine can be installed in the casing of a pocket radio. A 10cm long plastic flexible wire is welded to the grid of VT1 and extended out of the casing to serve
as an electric field induction piece. After assembly, place it close to the phase line of the 220V AC power supply. If the speaker has an alarm sound, it is working normally and can be
used. In order to ensure safety, the alarm should be electrically tested before use, that is, it should be close to the phase line of the AC 2ZOV power supply. If it can alarm the police, it can be used.