How to Make an AC Line Detector





Introduction: How to Make an AC Line Detector

About: HI! I am Junez Riyaz, currently doing Bachelor of Technology in the field of Electronics and Communication Engineering. I am much interested in inventing something new yet from my childhood. In my leisure ti...

AC line detector is a device which detects AC line currents without making any electrical connections to the line.

An easy to make circuit to identify the line and the neutral of an AC circuit, without making contact with the wires.

For more projects subscribe my youtube channel [ Subscribe ]

Now I am going to instruct how to make an AC line detector with less number of components.

Lets Get Started..

Step 1: Components Required

9v Battery with Battery Snap - 1 [Banggood ]

LED - 1 [Banggood]

Transistor 2N3704 - 3 [Banggood ]

Resistors [ Banggood]

1MOhm - 1

100kOhm -1

330Ohm - 1

220Ohm - 1

Switch - 1 [ Banggood ]

Aluminium or Copper solid thin wire - 5cm

Copper Clad PCB - 1 [Banggood ]

Step 2: Circuit Construction

I attached the PCB layout ,you can etch the pcb .

You can download complete pcb schematic here [ Download ]

To know how to make a pcb [ Click Here]

Install the components as per the layout.

Solder it carefully, because this circuit is highly sensitive .

Step 3: Construction and Testing

Feel free to comment.

For more projects subscribe my youtube channel [Click Here]



  • Clocks Contest

    Clocks Contest
  • Woodworking Contest

    Woodworking Contest
  • Oil Contest

    Oil Contest

We have a be nice policy.
Please be positive and constructive.




I might have had better results running it on a 9 volt battery and putting into a metal enclosure with the antenna sticking out but the circuit exhibited poor noise immunity when assembled on to a solderless breadboard I actually got a better result by eliminating the first stage and connecting the antenna to the second stage. I must add that I was working with this unit in front of my laptop and around some test gear on my bench so the circuit may just have picked up on ambient noise since it is not filtered.

Thank you for the post.

Super, now i come in this group, and they super DIY projekt,

I have some my DIY, electronics, optics and sl.

How to send here this project.


Sorry for my bad English.

Claudio from Croatia, city of Rijeka on the nordwest coast of Adriatiyc see


Can you explain how the transistors work to detect the AC line? Is it a frequency thing or a magnetic field thing?

1 reply

No, you need at least a coil or hall effect devices to detect magnetic fields. Here you detect any signal from very low frequencies to very high ones.

Basically looks like a Darlington Transistor setup with an additional transistor as well. So what you've done is make a huge current amplifier setup for huge amounts of gain. So even a little RFI off any wire will light the LED. And to answer one previous question, yes you can add a buzzer to the circuit to activate when RFI is detected. Just add it parallel to the circuit where the LED and current limiting resistor is. Just make certain the transistor can handle the addition current and the supply voltage can support the addition buzzer requirements and it will work.

2 replies

A 50 or 60Hz lowpass filter will avoid detecting radio frequencies.

Thank you for improving this instructables.

Component list shows a 330ohm resistor, but its not shown on circuit diagram. Can you explain why it's not mentioned please?

1 reply

hello, can i even added buzzer into the circuit?

1 reply