This circuit is highly useful to detect the presence of AC in mains wiring without making contact with AC line. The circuit can be used as a Non Contact AC tester to test the live and broken wire. It is highly useful to check breaks in the concealed wiring. The Flashing of LED indicates the presence of AC. The circuit can detect 50 Hz Ac hum from a distance of I foot.
IC CD 4017 is used in the circuit to detect 50 Hz AC Hum from the mains wiring. IC 4017 is a Johnson decade counter with 10 outputs. Its outputs become high one by one when the input pin 14 gets positive pulses. The IC counts only when its reset pin is connected to ground. When the Antenna connected to the pin 14 of IC is placed near a live wire, the AC hum will be picked up by the input pin 14 and the output of IC becomes high one by one. This causes the transistor T1 to conduct and LED starts flashing to indicate the presence of current .
Antenna can be 10 cm plastic wire or a telescopic antenna used in radio
Caution: 230 Volt AC can give a lethal shock. Do not make direct contact with plug points or exposed wire ends. Keep the Antenna 1 foot away from the Ac line.