Metal Detector Schematic Diagram. The circuit utilises two rf oscillators. A faraday shield may be added to reduce ground effect and capacitive coupling and this is wired to 0v.
The 555 ic timer here acts as a square wave generator and it generate pulses with frequencies audible to human. Although the metal detector circuit with the 555 timer integration is simple it works very well. Simple metal detector project metal detector circuit diagram.
Pic12f1840 still usable also.
As shown the circuit oscillates at around 230khz. It is possible to make either pinpointer or a full size metal detector based on this circuit. How to diy one of the best metal detector circuits is a premium interactive video tutorial. Read this post to get good idea about circuit diagram of metal detector.