Detects the presence of a live mains conductor
Minimum parts counting
Circuit diagram:
Parts:
|
C1 |
100nF 63V Polyester or Ceramic Capacitor |
|
D1 |
Red LED (any type) |
|
IC1 |
4017 Decade counter with 10 decoded outputs IC |
|
P1 |
SPST Pushbutton |
|
B1 |
3V Battery (two 1.5V AA or AAA cells in series etc.) |
|
Sensing probe |
3 to 15 cm. long, stiff insulated piece of wire |
Circuit operation:
If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10.
When remote from a live line, the unit stops counting, the LED resulting permanently off.
Notes:
- Sensitivity can be varied using a more or less long sensing probe.
- Due to 3V operation, the LED's current limiting resistor can be omitted.
