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