This is a fascinating circuit, originally from the IEEE Engineering Sciences & Education Journal Vol 8 No 1 Feb 1999 pp25-26.
I’m working from a demonstration by w2aew.
It actually builds on the basic StairStepGenerator project and adapts it to perform basic NPN BJT curve tracing -
plotting collector currect to collector voltage for different base current values.
It generates curves like this..
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub