on video How to make a wireless AC voltage detector || wireless voltage detector

 How to make a wireless AC voltage detector || wireless voltage detector

In this video, we'll show you how to bold a simple age effective wireless AC voltage detector circuit using only to BC 547 NPN transistor, one 220k resistance, one LED, and 3.7 volt battery. This circuit can detect the present AC voltage in a circuit without recurring direct connection with the live wire.

The working principle of the circuit is based on the fact that the voltage applied to the base of the first transistor can be used to control the voltage level at collector of the second transistor.

When AC voltage is applied to the base of the first transistor, it acts as an amplifier to increase the voltage level of the signal. The second transistor further amplifies the signal and send to the LED circuit. The LED lights up when AC voltage is detected, and turns off when there is no AC voltage.

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.

2 BC547 transistors

LED

220 Ohm resistor

Spring (ballpoint spring or copper wire)

9V Battery

9V battery clip

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

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.

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.

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.

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.

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.

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!

 How to make a wireless AC voltage detector || wireless voltage detector

In this video, we'll show you how to bold a simple age effective wireless AC voltage detector circuit using only to BC 547 NPN transistor, one 220k resistance, one LED, and 3.7 volt battery. This circuit can detect the present AC voltage in a circuit without recurring direct connection with the live wire.

The working principle of the circuit is based on the fact that the voltage applied to the base of the first transistor can be used to control the voltage level at collector of the second transistor.

When AC voltage is applied to the base of the first transistor, it acts as an amplifier to increase the voltage level of the signal. The second transistor further amplifies the signal and send to the LED circuit. The LED lights up when AC voltage is detected, and turns off when there is no AC voltage.

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.

2 BC547 transistors

LED

220 Ohm resistor

Spring (ballpoint spring or copper wire)

9V Battery

9V battery clip

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

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.

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.

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.

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.

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.

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!