How to determine a good "ground" for your experiments? But if the ground is good, then can it be used as an additional power source? The answer to these questions are to be found using unusual devices are described below.

In fact — it's a bit modified "kacher Brovina"=> instead of linked coils there is applied a coaxial cable wound on the ferrite, and the bias circuit transistor added chain R2C2 responsible for starting the generation of the appearance of the land.

The transistor VT1 for a bunch of "indicator ground + economical flashlight" the best use КТ805БМ, because it is more sensitive for different "land." If you make just economical flashlight that will fit any transistor, for example, KT315 or 2SC945.

The VD1 diode — any ultrafast, for example, UF4007. Led VD2 should be designed for a voltage of 3 to 3.6 volts and to give power 1 .. 3 watt, for example — GBZ-10W.

Coax CL — a thin coaxial cable with a length of 0.7 .. 1 m wound on a ferrite ring or on any ferrite core. When winding should be guided by the principle of maximum filling of the entire surface of the ferrite. Here it does not matter the number of turns, because the generator itself will adjust to the winding. Ferrite need to artificially increase the length of the coax.

Powered by one AA size battery grade AA (or AAA) 1.5 volt. Can be fed from two batteries or from a single 3 volt, but instead of one led VD2 will need to install two, connected in series.

The setup for the indicator ground to produce the resistors R1 and R2 achieving maximum difference in the LEDs between disconnected and connected the "ground"; when off the ground it should be off. If the scheme is only used as an economical flashlight, the configuration is reduced to setting the brightness of the led the resistor R1.

An interesting effect can be observed if a disconnected ground, the resistors R1 and R2 to achieve the weak glow of the indicator, and connecting a more than bright; the power consumption is almost not changed. — More qualitative grounding will cause a brighter glow of the led.

In the design of the device, as the R1 you can use a variable resistor with a switch, then it will serve as a threshold device to identify "ground", and a regulator of illumination, and, in fact, a switch.

Another option schemes sent Vladimir Lukasina. Further, I provide the original text and photos from the author.