A metal detector is a device that is capable of detecting metal objects near its search head. Some more advanced are even able to discriminate between metal types. This Diploma is constructed out of three parts. In the first part, the theoretical background of metal detectors is introduced. It is followed by a Hardware and software part.
In the first, I described a short history of metal detectors, how they work and what kind of metal detecting technologies are used today. Basic properties like coil types, coil sizes, and operating frequency are also mentioned in the first section.
In the second section, we dive into the designing and production of the circuit. For signal generation, the Wien-Bridge oscillator is used. It generates a stable sinusoidal signal of pre-calculated frequency. The generated signal is connected to the transmitter coil. The signal that is picked up by the receiver coil is then connected to amplitude and phase detection circuits, which help us transform signal changes into a more digital-friendly signal. These two values are important for metal discrimination. Transformed signals are then connected to the analog pins of the microcontroller.
The operation of the microcontroller is described in the software part. AD converter is used for the conversion of phase shift and amplitude change signals. The microcontroller is also used for PWM signal generation, which is connected to the Buzzer. If there is a metal object near the search head of the metal detector, the buzzer will produce a sound. There are also two buttons. The first one is used for mode selection, and with the second one, we can set the reference values.
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