[Dzl] and his rather serious looking son are metal detector enthusiasts. But when they couldn’t find their store-bought metal detector earlier this summer they just went ahead and built their own. [Dzl] starts his write up with an explanation of how most oscillator based metal detectors work. 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. When metal enters the coil it alters the frequency, which is immediately picked up the Arduino. Instead of that characteristic rising tone this rig uses a Piezo buzzer, issuing the type of clicks you’d normally associate with a Geiger counter.
The last part of the build was to find the best coil orientation. They settled on thirty turns around a metal bucket. An old Ikea lamp is the perfect form factor to host their hardware which seems to work like a charm.