MICROCONTROLLERS

Just remember, Johnson Noise (aka: Resistor noise) and Reverse-avalanche Shot noise (aka: Zener Diode reverse current) are both quantumly random events at fundamental physics levels. So you can get fundamental "true" RNGs using a cheap Zener diode.

Johnson Noise is very small though, so if you try to amplify Johnson noise, its probably going to be other noise in your system in practice (ex: P-N junction noise in your transistors/amplifiers). So I think the Zener Diode noise generators are the most elegant solution.