@Circuitfantasist Just now I skimmed my ECG project log and found the whole documentation file is about 350MB large. I am thinking of using AD5933 impedance tester to confirm some of my old experiment results. I quickly skimmed the basic stuff to refresh my memory. I usually recommend fellow hobbyists to start with this very good tutorial:

The triangular wave is sharp and stable, much better than that much more complicated and unstable ICL8038 and NE555 circuits.

Next step is to use this triangular wave voltage to power the tunnel diode and see if I can watch the electrons swimming through the tunnel. :) Many thanks for your inspiring suggestion. Ah, jogging and supper time. See you later. Cheers.

OK, this is a possible solution. In the Lancaster's "elegant simplicity", a neon lamp serves as 7414. You can see the general idea in many everyday situations. Now, you need my 90's V-to-I module - a buffered inverting amplifier with a tunnel diode in the place of R1. I will publish a paper and post about it... also, about the "simplest IV curve tracer"...