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Metal detector using frequency counter and OLED display

There are a lot of forests in Lithuania which I like exploring on my bike. In the past a lot of Lithuanian resistance troops resided in those forests, so there is a big probability to stumble upon a stash of some kind. However that stash might as well be a grenade or a bomb of some kind, but nevertheless I always wanted to combine my motorcycle riding through the woods with treasure hunting and some time ago I decided to build a simple metal detector. Granted there are lots of metal detector designs, like BFO, VLFD, PI and so on (I'll briefly cover some of them in the theory section). Some of them I've tried in the past with various results and then during one boring evening of browsing the internet I stumbled upon this blog and decided to build this type of metal detector. The design is really simple - there is a simple oscillator circuit and a frequency counter. When the coil passes over or near various ferromagnetic or paramagnetic materials the frequency of the oscillator changes and based on this change you can decide where to dig. Moreover since the frequency counter can be implemented on any microcontroller you can analyse the frequency change in many different ways potentially enabling metal differentiation and even filter out frequency drift, that plagues other types of detectors.