[Dedevil]

I will try to draw my idea of how i would build it and post, but i have never built it.

I read it in a old book on magnetism which I do not have now.

Most references say you must use special scientific labratory equipment, but this is the basic idea behind this special equipment. It is a device that detects the local magnetic fields by cancelling the earths magnetic field.
This would give you an idea of what magnetic materials are in the local ground, but will not work if your ground is mineralised.

Where (which country are you trying to detect)? Can you show us photos of the soil or landscape?

Tell us a bit more about the iron boxes?


rgds