yes it is but that's a really complicated process and i wouldn't recommend anyone to try it. they might end up with something that doesn't even work right and has low entropy!
Actually it's not complicated at all. Of course your average Joe won't build his own avalanche noise PCB, but someone with electrical engineering skills should be able to whip a circuit up and order a PCB within an afternoon. It's honestly a simple circuit.
I just made a quick web search and seriously surprised that there's no ready-made PCB / DIY kit or similar, that you can plug in and get randomness e.g. through cat /dev/tty.usbrandomdevice.
probably because it is a real pain to make them and they would have to charge so much that no one would buy it they would just buy something like this:
https://www.amazon.com/TrueRNG-V3-Hardware-Random-Generator/dp/B01KR2JHTATrust me, it's not a pain. Foundation Devices have such circuits in their hardware wallets and the USB RNG you linked to, may have the exact same thing inside it, as well.
I appreciate the
open-source and verifiable avalanche noise source (actual circuit from few simple components) on the Passport hardware wallet.
And obviously the ability to import your own custom seed phrase. This allows you to generate it with dice or whatever you deem secure.
But again; these avalanche noise circuits are amazing. You can literally see them on the PCB, take an oscilloscope to it and verify that it does what it's supposed to and that there's no deterministic bullshit going on.
i heard someone made one using a geiger counter and detecting radiation. not sure how hard that is to diy. but maybe it's simpler than this zener diode thing.
Sampling radiation measurements won't be much simpler than sampling the avalanche noise source, and you'll need specialized components.