Non-Contact AC Voltage Detector using 2N3819 MOSFET

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In this tutorial, we are making a very useful and easy project for a Non-contact AC voltage detector. This circuit will blink an LED and make a sound (beep-beep) when any AC field is detected. It will also show the phase and neutral wire from the two AC wires by making a beep sound and the LED blinks only on the base wire whereas on the neutral wire, it stays off.

The main components of this circuit are FET 2N3819, 555 timer IC, some resistors, and capacitors. FET or field-effect transistor is a transistor that uses the electric field to control the flow of current. The 555 timer IC is used to provide oscillations or short/long time delays in a circuit.

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Hardware Components

The following components are required to make an AC Voltage Detector Circuit

S.no	Component	Value	Quantity
1.	DC Supply	6-12V	1
2.	Antenna	2-4 inches	1
3.	Transistor	2N3819	1
4.	IC	NE555 Timer	1
5.	Resistor	1M, 10K, 470Ω	1, 2, 1
6.	Electrolytic Capacitor	10µF	1
7.	Ceramic Capacitor	0.01µF	1
8.	LED	–	1
9.	Buzzer	–	1

2N3819 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3819

NE555 IC Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 555 Timer

AC Voltage Detector Circuit

Working Explanation

The operating voltage of this circuit is 6 to 12 volts DC. The 2N3819 FETs work as AC field detectors. When the charge around the circuit is detected by the antenna it sends it to the gate terminal of the transistor. Now the transistor will provide voltage to the 555 timer IC and it will activate. The beeper circuit is built around this IC so when the IC activates it will blink the LED and the buzzer will start producing a beep beep sound, giving an indication of the detection.

The time period of LED and buzzer activation is set by the values of the resistor and capacitor used at the input of 555 IC. It can be increased by increasing their values.