Simple circuit to detect electro magnetic field?

Question

I'm need to make a simple circuit to make a light (probably led) turn on in the presence of an electro magnetic field. Anyone know how or where I can get plans?

Answer 1

you could use a transformer principle if the field was alternating, if you placed a coil within an alternating field a voltage would be induced. if it was great enough you could use it to power a bulb. The voltage induced depends on the number of turns in the coil and the magnetic field intensity.
if the field was constant then you would have to move the coil within it

Answer 2

The simplest circuit contains only to items.
a 100micro amp meter and a small coil of wire.

Take a foot of # 18 wire, strip both ends. Leaving an inch and a
half of wire on each end, wrap the wir around a pencil.
Connect the ends to the meter.

Voila! Electro magnetic detector.

Answer 3

Here are some units:
http://www.circuits.8m.com/RC.htm

Here is a circuit:
http://www.redcircuits.com/Page55.htm

Good luck with your project

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