Updated & put on my website: "Mar 25, 2012"
This circuit is Quite Stable, Quite Sensitive and Physically Small. Also 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 off.
This circuit uses a 555 Timer to give a Timed Output using a 25K trimpot for aproximately 1 to 8 seconds, with the values shown, However these values can be changed for different On-Times.
The Circuit operates at 12 volts and drives the load with a Mosfet, so it can handle Several Amps.
Since this Circuit works on Body Capacitance,
An Earth Ground is Essential for Proper Operation and Best Sensitivity.
Just the "PCB", and/or a "kit of Parts/PCB" are Available from me. Email me for current prices.
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