Mr BiJuT is what I’m calling my freeform realisation of a simple NPN/PNP transistor testing circuit.
This is a nifty little design that I found in the Radio and Electronics Cookbook. It is one of those circuits that is the height of simplicity but is also quite tricky in it’s own way! Whether you immediately “get” how it works depends very much on how you draw the schematic;-)
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub