User manual

67 3 Operation and Functional Principle
LEDs
The LEDs give you some information about the type of
the detected metal. The white LED (at the edge of the flap
lid) indicates with high probability a so-called ferrous metal.
The blue LED (in the middle of the flap lid) indicates a prob-
ability for a so-called nonferrous metal. However, large,
planar objects containing ferrous metal may also cause the
blue LED to light up.
Functional principle
The circuit of the metal detector consists of a free run-
ning LC oscillator (CD 40106) and a digital frequency coun-
ter (HT46F47E). The oscillator frequency (approx. 400 kHz –
650 kHz) depends mainly on the search coil. When a metal
object gets near the coil, the frequency of the oscillator
changes. If the object consists of a ferrous metal, the oscil-
lator frequency drops. If the object consists of a nonferrous
metal, the oscillator frequency rises. As mentioned before,
large, planar objects containing ferrous metal may also
cause the cause the oscillator frequency to rise.
The frequency generated by the oscillator is counted
by the microcontroller. Any frequency variations are indi-
cated visually and acoustically.