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...
![](metal.jpg)
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