grid dip meter schematic

Hi,

I want to build a security system which detects when an object is 'out of reach'. The range should be 1,5 - 2 meter.
What about the grid dip meter method? When the object (with the LC resonator inside) leaves the area, the electromagnetic field changes.

Does anybody have a schematic? I prefer to make the reader and the tag myself.

Patrick

This method relies on inductive coupling. The range will be a few cm unless both coils are very large. By large I mean a diameter of at least half the distance you want to cover.

This may not meet your needs. If you can have a battery in the object things are better. You can receive a signal at frequency F and retransmit it at F/2 and get much more range with smaller coils.

What kind of OBJECT .. a PERSON ? or a thing

There is the Thermic RADIATION method is pretty good .. you can detect
temperature variations with thermopiles!