I found various circuits online (1, 2), but they seem rather complicated.
Would this work..?
Would this minimal NPN-based metal-detector circuit work
bjtdetectionnpn
Related Solutions
Buy this book The Art of Electronics by Horowitz and Hill (2nd edition).
It cost $US20 (which is a bargain). It's in New Delhi and they have a number of them. If you cannot afford the 1050 Rupee get several friends to buy it together, This is the best book on the subject that you will find.
- The Art of Electronics (Second Edition)
(ISBN: 0521689171 )
Paul Horowitz,Winfield Hill
Bookseller: BookVistas (New Delhi, DEL, India)
Bookseller Rating:
Quantity Available: > 20
WARNING" There are a lot of these also advertised in India. They cost typically the same or more as what I recommended and are not the same. Take due care. This the associated student manual by Horowitz and Hayes. If you can afford to buy one of these AS WELL do so but get the proper textbook first. Copy of workbook here for Rs484 including postage in India.
Maybe it's a 2SC1740: -
If so, note the pins (red line) - they are not the standard pin-out with base in the centre like the 2N222A: -
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Best Answer
No - or at least not like you expect. I was writing a long explanation of why not and the physics, but then I accidentally pressed a button and lost it all...
So instead I'll point you to two things you need to understand:
Eddy currents: http://en.wikipedia.org/wiki/Eddy_current
How Metal Detectors Work: http://electronics.howstuffworks.com/gadgets/other-gadgets/metal-detector2.htm
Pay attention to the fact that it produces an AC field which makes eddy currents come far more naturally.
Your circuit will produce a DC loop.
Technically, it will work... but only as you're moving it [quickly] and only with tiny, tiny, tiny current fluctuations making tiny, tiny, tiny sounds.
For reference, these forums generally assume you know at least some of the physics/mathematical/electrical background of the subject matter, but it sounds like you have only an idea that "transistors and coils do stuff." I'd strongly recommend finding old textbooks on these subjects and reading more about it, starting with an overview of Physics Electricity and Magnetism and going to the abstractions of AC/DC fields and inductance, then transistors.