Random Reference Diagrams

Random number generators sample a source of noise ("random" or "high entropy" information) and convert it to numerical information.  A block diagram of the system looks like this:

A random source (noise) is sampled by a transducer, converted into numbers, then emitted (or stored) as a data stream for present or later use.

The model has been around for a very, very long time.  A Real World™ example is a board game.  The noise source (dice) is sampled (are rolled), transduced (seen by eye), counted (computed), and the output number used to move the pieces around the board[1].

This model is basically what the National Institute of Standards and Technologies employs:

NIST Beacon Architecture, 2013[2]

For a hobby project, beehives and quantum entanglement sources are a bit out of reach.  They both require care and feeding.  Bees go to sleep at night.  Seems likely neither is a simple choice.

Noise generating electronic circuits are a choice.  The classic example is a white or pink noise generator.

Simple White Noise Generator[3]

Pre-made noise generators cost anywhere from $2 up to hundreds or thousands of dollars depending on specification[4, 5].

These circuits are simple and reference designs only require soldering and Amazon skills.  Tuning and using these tools may require a little effort.  But ... they're boring black boxes.

What can be built using parts already on hand?

Notes

1. Rolling two dice makes a nice, pyramid-shaped "normal" probability curve. 1/36 to roll a 2, 2/36 to roll a 3, 3/36 to roll a four, and so on:
   
2. NIST Randomness Beacon, 2017
3. "Simple White Noise Generator", EE Web, 2013
4. White Noise Generator, Ali Express
5. RF Noise Generator, TechToolSupply, 2018