I built this circuit. Different versions of this exist on the internet, some using an MPF-102 JFET instead of the 3 NPNs. The various sites describe it in several different ways:
- "mains hum" detector
- static electricity detector
- "detects the presence of your hand without any physical contact"
- an "electronic electroscope"
- electromagnetic field detector
- EMF detector
- electrical noise detector
- "DC radar"
- "E-field detector"
- finally as a ghost, spirit, "aura" or "paranormal energy" detector!
The one I built behaves very strangely.
The LED lights if I hold the the circuit board and move the probe near a solid object. If I put the board on a table, it doesn't light as much, but it seems that any object with static electricity will light the LED if I rapidly move the object towards, away from, or back and forth near the probe.
A cotton towel does not light the LED and neither does any metal object, but my acrylic sweater does, and my hand will light it each time I scuff my feet on the nylon carpet.
It seems to light up especially bright when I jiggle a polypropylene plastic cup near it and will light when I either move the plastic cup quickly toward the probe, or hold it close to the probe then quickly move the plastic cup away.
If I hold the plastic cup still near the probe the LED goes out, then if I wiggle the plastic cup around the LED comes back on.
Despite what some of the web sites note, the LED does not light if I bring a plugged-in electric cord near the probe when the board is on a table.
Does anybody know what this actually "detects" and why it behaves as I've described?