Hello,
I want to make a sensor which can sense iron piece(3cm*3cm)3cm under sand. The sensor should be such that it doesn't sense other iron pieces which are placed aprox. 5cm away from each other(considr pieces placed at each corners of a square).

Plz. tell me some websites available for making such circuits.

Thanks in advance.
Bye

 

You might want to try the conventional metal detectors (with beat frequency oscillators), that give an output in the audible range in response to the detection of any metal object. The range you require needs some precise electronics though.

Here's a link to building a metal detector from scratch.

http://www.sas.org/E-Bulletin/2003-06-20/labNotes/body.html

However, this is still not a complete solution to ur problem of precision detection.