This one differs by using an Arduino to read from the metal detecting coil. The circuit starts with an oscillator that produces a signal of about 160 kHz which is constantly measured by the Arduino.

An amateur metal detectorist discovered a buried hoard of nearly 1,500 Roman coins near Bucharest, Romania. The coins, which ...

metal detector uses transmitter and receiver coils in so-called Double-D geometry. The transmitter coil is driven by a signal generator module that operates at its resonant frequency of 4.74 kHz.