I’ve always wanted to take pictures through a microscope so I can see what tiny screws and coins look like when magnified, but I don’t have the money to purchase that kind of equipment.
The first spectroscopes used glass prisms to split light into colors, but Fraunhofer found that an array of closely spaced wires had the same effect. Today we call these arrays of tiny slits diffraction gratings.
This project by Collin uses a familiar schematic — the light-sensitive oscillator (aka “phototheremin”) as originally described in Forrest Mims’ book Timer, Op Amp and Optoelectronic Circuits & Projects.