User manual

3 Operation and Functional Principle

The micro controller stores the measured frequency

as a numerical value and processes it. In theory, a maxi-

mum numerical value of 16,777,215 (3 byte = 2

) may be

captured in a single measurement.

This corresponds to a resolution of 24 bit. By inserting

jumper J1 the internally processed numerical values are

divided by 2. As a result, the sensitivity of the metal detector

is reduced.

Depending on environmental inﬂuences, LC oscial-

lators tend to slightly change their frequency (dri). Such

small frequency changes are compensated for by the mi-

crocontroller soware. In the process, the following phe-

nomenon may occur: When you approach a metal object

very slowly, the soware interprets the generated frequen-

cy deviation not as an indication of a a near-by metal, but of

a spontaneous dri. Detection is only indicated temporarily.

When you now increase the distance to the object, you get

a permanent visual and acoustical indication of a metal ob-

ject that is no longer there. In this case you should turn the

knob until both LEDs light up and the microcontroller is sort

of restarted (executing the initialization routine).

The automatic compensation for frequency dri is

also the culprit when the LED does not light up during the

actual detection of a metal object, but blinks shortly when

you withdraw from the object. As long as the LED lights up,

an audible signal is emitted.