Simple Metal Detector

It's a simple metal detector design that has the quite good characteristics. the principle of operation which one differs from the classic schemes (BFO, transmit-receive known as "two-boxes" metal detector, inductive).

The dynamic mode is used to find targets in interference environment. There is known from theory of signal filtration that if signal shape is determined we can construct optimal filter - the best one for extracting the signal with maximum signal/noise ratio. This filter is known as optimal matched filter. In our device we realized digital optimal matched filter as part of microcontroller software. The filter parameters are optimized for effective ferro- and nonferro targets detection on 0.5-1.0 m/s velocity of sensor.

Features of the Metal Detector:
Power supply .............................4.5-6V;
DC consumption .......................15 mA;
Indication ...................................sound + 8 LEDs;
Modes ........................................static or dynamic;
Discrimination.............................ferro/non-ferro.

Metal Detector Schematic, Layout and PCB

Switches controled (versions V1.9 and V2.0 of firmware):
S0: reset device;
S1: reserved;
S2: on - threshold hight, off - threshold low;
S3: measuring time on - 30ms, off - 120ms;
S4: selftuning on/off (in dynamic mode only);
S5: mode on - static, off - dynamic.