Introduction:

  All these voltage detectors work on a simple principle of electromagnetic induction.

A magnetic field is produced around a current carrying conductor and if current through the conductor is alternating current (AC), the magnetic field produced varies periodically. When we place an antenna near an AC energized object, a small current gets induced into the antenna due to electromagnetic induction. By amplifying this current we can light up a LED or a buzzer circuit, indicating that AC voltage is present.

we need:

IC 4017

2N2222 General Purpose NPN Transistor

100 μF Capacitor

LED

220Ω and 1K Resistor

Buzzer

and a Homemade Antenna

Connect Pin-1 of the IC to the 1K resistor. The other end of the resistor connects to the base of the transistor.

Next connect the collector pin to the -ve legs of the LED, Transistor and the buzzer. The +ve legs connects to the +ve rail of the circuit-board. The negative rail connects to the Emitter, Pin-8, Pin-13 and the Pin-15 of the IC. The antenna is connected to the Pin 14 which is the clock input pin. When the antenna receives input clock pulses it advances the counter and the LED flashes. You can connect the cable connected to Pin-1 to any one of the Output pins of the IC. If you want you can also connect 3 or 4 LEDs to the Output Pins to give it a chaser like effect.

Now lets do a quick test. Moving a live wire close to the coil makes the buzzer and the LED to flash. But as you can see, at some instances the LED and the buzzer wont go off even after I move the wire away. Also, this setup flashes when I put my fingers around the coil. Pretty much every second video on YouTube is made using this hypersensitive IC. But frankly speaking I am not impressed by this setup.