Simple
Metal Detector
By: Steve and Rachel Hageman
Have some fun! The Kids love this very simple metal detector. You can
make it in an evening and be hunting treasure tomorrow...
The
detector in action...
This simple circuit
works by heterodyning two oscillators together. The fixed oscillator
is used to tune close to the search oscillator. A low tone is heard
in the earphones. When the search oscillator is brought close to a
metal object, it's frequency changes. The resulting tone change is
heard in the headphones.
While this metal
detector is not as sensitive as the high $$$ models at the outdoor
shops, it can find a quarter about 1-2" below the surface of dry
sand. It's great fun at the beach or local park.
In the photos above
(not a very good photo mind you, but you should be able to get the
idea) you can see how we made our detector. PVC pipe was used to make
the handle. A small piece of copper tubing was used for the search
coil and the electronics is housed in a small Radio-Shack box. The
Box has the tune control, volume control and on/off switch in
it.
Documentation
available is,
- Schematic of the
Metal Detector in PDF format.
This design uses a
mechanical 365 pF capacitor. The variable capacitor are getting
hard to find, search the web for "365 pf air variable capacitor"
or "dual gang variable capacitor".
- Schematic of
revised design that orginally appeared in EDN (December 1997) in PDF
format: Metal_2.pdf
The revision
replaces the obsolete LM389 with a LM386. This design uses a
common varactor diode for tuning.
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Modified -
7Jan02