I spent some time working on a "de minimus" Arduino RNG. Best I got so far measured microsecond discharge and recharge rates and times of a high Farad capacitor. Would like something with no external parts, or just used LEDs (which are also sensors, lol).
-
The fundamental mechanism that seems to work is using a fast clock to measure a slow clock. All hell breaks loose of course when they're the same clock.
It's a common approach. The NES/SNES/N64 CIC lockout chips used the charge/discharge of an R-C network as an entropy source.
