The Arduino samples the peak detector’s output and calculates the original pulse’s amplitude. Their webpage has copious details on where to get the parts, the software and how to make it.

A new Instructables page has been created to make an eco-friendly DIY metal detector using an Arduino Mega just been combined with a 3.2 inch TFT LCD touchscreen to provide a fantastic readout ...

And, of course, with an Arduino and some know-how it’s possible to build a metal detector that has every feature you could want from even a commercial offering.