This is for anyone interested in metal detectors at a cheap price.
I recently built one around a colpitts oscillator. I made the search coil a part of the oscillator. The output of the osc. was fed to a darlington pair which drives the buzzer.
When ever any metal comes in the range of the detector, it absorbs the energy of the coil.
This causes noise in the circuit whic is sounded by the buzzer. As in my case i have fed the darlington pair output to the ADC and then to the microcontroller 8051.
If anyone out here wants any info regarding the same please do ask.