Non-contact voltage detector is a handy device which is useful for indicating if there current running in the circuit or system.

it consist of three transistors which acts as a switch in the circuit which amplify the current detected and a parallel connection of resistor in a increasing manner from 220ohm to 1Mohm which minimize the current passing through in the circuit and minimizes the chance of a busted battery.

The first voltage detector was used to indicate electricity passing through the AC lines, power line, and telephone lines in order to communicate if this line is busted or damage.

so without further ado let us build this ingenious invention.

Step 1: The Materials Needed:

The materials needed are the following:

red LED

Momentary switch

battery holder (optional: Alligator clips)

project box

2n3904 transistor

9V battery

breadboard

universal PCB

Copper clad PCB

Resistors (220ohm, 1Mohm, 100Kohm)

Step 2: Circuit Diagram.

Just follow this simple and easy steps

Step1:

just follow the circuit diagram given.

Step 2:

Cut 1X2 inch and drill a hole in the middle of the copper clad PCB and strip, insert and solder a 3 inch wire in the middle.

Step 3:

follow the schematic above in placing the transistors and resistors, I've also put a picture on the transistors(collector, base, emitter).

I've done mine in a breadboard just to be sure.

and after you've tested the circuit and up and lighting

then lets transfer it into the PCB.

PS: if you're an experience fellow or a professional, then skip this step.

Step 3: A Brief Info About Transistors

A transistor is an electrical component that functions, most
basically, as a switch — in principle not so different from a light switch. Instead of a physical movement, however, a transistor is controlled by a flow of electricity. And unlike your basic light switch, a transistor can be on, off, or somewhere in between.

Most transistors have three connections: one for current in, one for current out, and one that controls the “switch.” The current flowing through a transistor can be larger than the current controlling it, so it can become an amplifier: Connect the input to a power source (like a battery), and the control lead to a weak signal (like a guitar pickup), and the output will sound like the control signal, only louder. Just how much louder depends on a lot of things, but a factor of 200 is routine. This number is called gain.

If you use the output from one transistor to control another, the gains multiply.
With two transistors, the ideal gain becomes 200 × 200 = 40,000, and with three transistors (as in this circuit), 200 × 200 × 200 = 8,000,000! That huge gain lets you use it to detect the tiniest movements of electricity — even those created at a distance by induction or static charge!

Step 4: Transfering It Into PCB.

Cut the Universal PCB into 5X18 holes and transfer your circuit from breadboard to PCB.

Step 5: Drill Holes!

In the project box, drill two holes, one for the LED and the other for the momentary switch.

on the side drill a hole in the middle and insert the wire connected with the Copper clad PCB into the project box.

now put all your circuit inside the project box and attach the 9V battery and lets give it a try.

Step 6: The Usage.

Warning: Experiment and have fun but never ever touch the copper strip to a bare wire that has live voltage!

Hold the non-contact voltage detector near a live AC power line and depress the button: it will light up.

The detector can be a little sensitive about the position it's held in so if the LED doesn't light up, try moving the detector around a little, while keeping the copper strip close to the wire.It's also fun to see how it detects static electricity. Try quickly rubbing your hand across some carpet several times then hold your hand near the copper strip. The LED should light up brightly from the static charge build up.

and that's how you make a Non-Contact Voltage Detector

as always Experiment and have fun.