A non-contact voltage detector is a useful tool to detect nearby electrical fields. It can detect the presence of AC power in cables, switches, outlets, and fixtures without touching them. It can even detect static electricity!
PART 1: ASSEMBLE THE CIRCUIT
PART 2: OPERATION OF THE CIRCUIT
A transistor is normally used as an amplifier or a switch. A small input current (from base to emitter) controls a much larger output current (from collector to emitter). The transistor therefore amplifies the input current.
If the output current of each transistor magnifies the input current by 300 times (BC548B typical gain is 200 – 450), the total amplification of the 3-transistor amplifier in the circuit is 300 × 300 × 300 = 9,000,000. This huge gain allows us to detect the tiniest movements of electricity — even those created at a distance by induction or static charge.
PART 3: DETECTING AC POWER
With the circuit from Part 1, hold the conductor plate near a live AC power line or an AC power plug that is switched on. The LED should light up, indicating there’s AC power present.
NOTE: If you do not have a conductor plate, you can temporarily use the bare end of the wire as a plate.
Never ever touch the conducting plate to a bare wire that has live voltage.
PART 4: DETECTING ELECTROSTATIC
The circuit can also detect static electricity. Try rubbing a plastic ruler or a balloon with a piece of cloth and bring the object close to the conducting plate (a bare wire conducting plate may not work well). The LED should light up from the static charge build-up.
PART 5: SOLDERING THE CIRCUIT
For details on proper soldering technique, see Guide: Soldering Technique.
STEP 1: Cut the circuit board to the required size: 12 holes × 9 holes.
CAUTION: Be careful when handling a sharp blade. Request help from a mentor if needed.
STEP 2: Plan how to lay out the components on the circuit board. It is better to spend some time planning to get the connections right. Otherwise, you may have to spend a lot of time resoldering components.