$$ f = \frac12\pi\sqrtLC $$
Download a simple PI detector PDF (search "Surf PI 1.2 PDF"). Study the 555 timer section. Order the components. Build it in one weekend. Nothing teaches you what is inside a metal detector like the smell of solder smoke and the first beep over a buried coin. Have a specific metal detector PDF you are trying to decode? Leave a comment below with the model number, and we will help you interpret the schematic. inside the metal detector pdf
Where is coil inductance (measured in microhenries, µH) and C is capacitance (picofarads, pF). A typical VLF coil might be 300 µH with a 0.022 µF capacitor, resonating at about 19 kHz. $$ f = \frac12\pi\sqrtLC $$ Download a simple
However, remember that a PDF is static. The real "inside" knowledge—how to null a coil to 5mV, how to compensate for temperature drift, or how to tune out a specific interference—comes from building the circuit and probing it with an oscilloscope. Build it in one weekend