You should first know a little about the 555 ic. There are totaly 8 pins in it. The pinout is given in this step.
Step 2: Collecting the things
This metal detector is very simple and is based upon a very famous and easily available ic which is 555 ic. The things that you will need to make this metal detector are
2.2 uf capacitor- 2
10 uf capacitor
8 ohm speaker
6 to 12v dc power supply
10 mh (milli henry) inductor/choke
Step 3: Making the metal detector
Assemble the circuit on a perfboard or pcb except the inductor. Attach two long wires at the place of the inductor. Use a long rod and place the inductor at the end. If you are still confused about the installing of the inductor and the circuit just see the picture. The schematic is given in this step.
Step 4: How it works?
If there is any treasure underneath your house or your garden or anywhere, now you can find it.This metal detector can detect metal as well as magnets. When a piece of metal or magnet is brought close to the inductor/choke the output frequency changes and you can hear sound from the speaker. The schematic and info were taken from talkingelectronics.com