This circuit is
- Quite Stable.
- Quite Sensitive.
- Physically Small.
- Very Cheap to Build.
Larger Antennas give Better Sensitivity.
For an Antenna using Smaller Objects, (Such as Door Knobs) use Input "A".
For Large Antennas, (Such as Large Metal Plates) Use may need to use Input "B".
The Sensitivity is set with the 500 Ohm trimpot.
And the Sensitivity is adjusted by setting the Sensitivity control so the LED is Just on the verge of going Out.
There is no Relay on the PCB, so it allows for connection to almost any relay.
However, Design this to Operate a Small Relay.
If the Relay you use requires a stronger coil current, you can Replace the 10K Base Resistor, Down to 1K ohm.
This will allow for Greater Conduction through the Transistor.
Since this Circuit works on Body Capacitance,
An Earth Ground is Essential for Proper Operation and Best Sensitivity.