At my contract job I had a task to build a medal detector for a mysterious device... While doing a research I found a promising project that I could use at a hackaday. This detector was based on a single BJT LC sine wave oscillator, really simple... First I made some simulations in LTSpice to check if it even generates. After this I build a prototype from a proto-PCB (Did not even bothered to use breadboard for this because of the capacitances on the contacts), I wined up some Kynar cable around plastic cup to make a big coil and... It worked!! I could see that the frequency of a generator changes in the presents of a metal (It rises or falls depending of the properties of a metal). Now I just had to made it work with Raspberry Pi, and here all the problems started... I could't force Raspberry Pi to measure frequency accurate enough (It was a ~150kHz signal). To solve this problem I used a timer in ATtiny as a frequency divider... (It was super wired to go back to programming micro-controllers without proper debugger and memory readout options - going back to basics!) At 15Khz Raspberry Pi did not have any problems with measurement. Unfortunately I did not made any photos of this project :(, I only have my spice simulations.