Wireless AC Current Detector

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Introduction: Wireless AC Current Detector

About: I am New Pew, I create electronic projects and share these creations on my YouTube channel. In every video I mainly show how you can make these innovative creations yourself! There is a description of each pro…

While making my previous Instructable (easy infrared proximity sensor) I figured out a few things about using 2 transistors in a row to amplify a very weak signal. In this Instructable I will elaborate on this principle which is also called the "Darlington principle".

In this circuit, an antenna (spring) is connected to the base of first transistor. When we place this antenna near an object that is AC energized, a small current gets induced into the antenna due to electromagnetic induction. This current triggers the first transistor. Output of the first transistor triggers the second. The second transistor switches on the LED indicating that AC voltage is present.

Video tutorial

Supplies

  • 2 BC547 transistors
  • LED
  • 220 Ohm resistor
  • Spring (ballpoint spring or copper wire)
  • 9V Battery
  • 9V Battery clip

Step 1: Connecting the Transistors

Describing this step is very laborious. The images make it a lot clearer!

  • Bend the collector of transistor 1 ninety degrees
  • Bend the base of transistor 1 all the way over the transistor
  • Bend the collector of transistor 2 ninety degrees
  • Connect the emitter from transistor 1 to the base of transistor 2
  • Connect the collector from transistor 1 to the collector of transistor 2
  • Cut off the protruding ends
  • Bend the protruding end where the collectors are connected 90 degrees

Step 2: Connecting the Resistance

The second transistor controls the LED. A resistor must intervene here to protect the LED. In this circuit I am using a 220 ohm resistor.

The resistor can be placed in front of or behind the LED and works the same in both directions. To keep the whole compact so that it can be placed on the battery connector later, it comes directly after the transistor.

  • Solder the resistor to the emitter (output) of the second transistor.
  • Bend the other pin 90 degrees and cut it shortly after the bend.

Step 3: Connecting the LED

  • Bend the anode (+) of the LED 90 degrees and cut it to a few millimeters.
  • Solder the anode to the resistor.
  • Cut the cathode (-) to the same length as the pin protruding from the connected emitters.

The 2 protruding pins should have about the same pitch as the 2 connectors of the battery connector. This is because the whole can be mounted on the battery connector later.

Step 4: Prepare the Connector.

The whole is mounted on the connector in the next step. For this, the connector must first be adjusted a little.

  • Cut the wires coming out of the connector.
  • Drill 2 small holes of about 2 millimeters through the connector.

Step 5: Mount the Connector

  • Slide the 2 protruding pins through the connector.
  • Solder the pins to the connector.

The pin of the collectors to the + connector, the pin of the cathode of the LED comes to the - connector.

Step 6: Install the Spring

A spring is attached to the base connection of transistor 1. This will function as an antenna to receive the electromagnetic induction from the AC circuit.

  • Slide the feather over the base and solder the connection.

If you don't have a feather, you can also make a spiral from, for example, a piece of copper wire.

Step 7: Ready

The Wireless AC Current Detector is ready! You only have to click it on the battery and you can use it.

Note that this is a hobby project to understand how transistors work! Always use approved tools when working on an electrical installation!

Update: User raddevus made a schematic of the circuit, it is included in the pictures of this step. Thanks raddevus!

Video tutorial:

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6 People Made This Project!

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41 Comments

0
acheide
acheide

10 months ago

Nice Instructable. At what distance will this detect a live AC wire?
Thanks.

0
Lee Wilkerson
Lee Wilkerson

Reply 8 months ago

It won't unless that live wire is radiating EM waves.

0
NEW PEW
NEW PEW

Reply 10 months ago

Onloy a few millimeters. You can add an extra transistor but than it reacts to any touch..

0
falk_m
falk_m

Reply 10 months ago

Doesn't the number of windings in the spring determine the induced current? (Would explain the poor result of that tarantula)
https://en.wikipedia.org/wiki/Inductance#Inductanc...
Maybe one can increase range with a better solenoid...

Anyways, thanks for the instructions! I am also trying to understand these tiny amp circuits, and I will certainly give your little gadgets a try.

0
JohnC430
JohnC430

Reply 10 months ago

you dont want to increase the range. after all this is intended to establish if current is flowing in just one specific conductor. imagine if the range is increased, what will it pick up?
Think of an oscilloscope probe when you touch the probe tip.

0
Lee Wilkerson
Lee Wilkerson

8 months ago

Great and simple project, but I would call it an RFI sniffer. The antenna will pick up all sorts of EM interference and noise.

0
Maxgi22
Maxgi22

10 months ago on Introduction

excellent project and clear and exhaustive description

0
charlessenf-gm
charlessenf-gm

Question 10 months ago

Hey, I like it. Most of these 'circuits in the air' can be a bit confusing (which side/leg of the LED is the Anode?!) but they are fun to watch and speak to a level of creativity at a 'whole 'nother level' The Zen of Electronics! Transcendental even.

I did wonder if the ball point pen spring needed to be positioned as it was, or could be pointed "co-axially" if you will with the battery (the same with the LED) or if the positioning had something to do with the need to keep connections as short as possible as well as from interfering one with another?

0
ElectroFrank
ElectroFrank

10 months ago

As several people have already mentioned, it is totally unsafe to have a bare spring as your probe. Please cover this spring with 2 layers of heatshrink at least, extending well past and closed at the end, in case of accidental contact with a live lire.

Many people on this site are not electricians, and do not fully understand electrical safety (yourself included). This is not an insult, it is a safety warning.

Look at all commercial products of this type, and you will see that the probe is fully insulated to prevent any possible contact with the AC circuit.

0
itscolin46
itscolin46

Question 10 months ago on Step 7

Why don't you draw a "circuit diagram"?

0
ELECTRONFLYER1
ELECTRONFLYER1

10 months ago

Please include a schematic

0
raddevus
raddevus

Reply 10 months ago

I created a schematic for this. It was a bit difficult to see everything but if you get a chance, take a look and let me know if it looks correct to you.

0
JohnC430
JohnC430

Reply 10 months ago

yeah it looks correct. Thanks.
following what he did is very tedious but you fixed that for all of us.

0
NEW PEW
NEW PEW

Reply 10 months ago

Thanks Raddevus!!

0
raddevus
raddevus

Reply 10 months ago

By the way, feel free to click on the schematic image (so it will be larger), take a snapshot and add it to your great article.

0
jott_1
jott_1

Reply 10 months ago

I vote for a schematic too.

0
NEW PEW
NEW PEW

Reply 10 months ago

Attached to the last step. Credits go to raddevus!

0
tschacherbat2
tschacherbat2

Tip 10 months ago

The addition of a AC capacitor of at least 400v would be in order for a safety precaution in case you happen to get near an uninsulated conductor. This circuit is good to use as a short circuit detector also if Q1 is replaced with a JFET. Simply disconnect wire harness at either end of it and connect one end of that harness to a low voltage current limited AC signal generator.

0
JohnC430
JohnC430

Reply 10 months ago

A 400 volt small value eg 1nF cap sounds like a good idea However, how do you check for a short circuit with only one conductor? and replacing Q1 with a JFET does what? it does not work in this circuit.