Contactless AC Mains Detector Relay Switch

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In this tutorial, we are making a contactless AC mains detector relay switch circuit. When an AC voltage is present in mains supply lines this circuit will be activated and deactivates when the AC voltage is not present. All of this work is done without making any contact with the main supply because the circuit is able to sense the electric field around the wires. This saves from the risk of electrocution or mishandling wires.

In this circuit, we are using a relay switch at the output of this circuit, so that you can connect any AC/DC equipment with it and control it with the circuit. You can either activate or deactivate this equipment when the AC voltage’s presence is detected with the help of this circuit.

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Hardware Components

The following components are required to make AC Mains Detector Circuit

S.no	Component	Value	Qty
1.	Input Supply DC	9-12V	1
2.	Opamp IC	LM358	1
3.	Transistor	2N3904	1
4.	Antenna	6-inches	1
5.	Relays	–	1
6.	Diode	1N4148	1
7.	Resistor	470KΩ, 1MΩ, 1KΩ	1, 1, 1
8.	Electrolytic Capacitor	47µF	1

LM358 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of LM358

2N3904 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904

AC Mains Detector Circuit

Working Explanation

This circuit is working on the basis of a high gain amplifier IC i.e., LM358. The circuit is draining very low power and in standby mode, it only consumes around 0.5mA due to the features of this IC. you can operate this circuit at any voltage ranging from 9 volts to 12 volts DC. An antenna is used to detect the presence of AC voltage. When the AC voltage is present the circuit will activate and the transistor is acting as a switch for the relay. So when the transistor activates the relay switch will activate too and the AC/DC equipment connected with it will start operating.

The sensitivity of this circuit is adjusted with a 1M variable resistor. It can also be increased by increasing the length of the antenna wire to 2-3 inches.