White noise source, level comparator, pulse generator. White noise is generated with a reverse biased transistor junction and amplified. A comparator produces a pulse whenever a threshold is crossed. The time period of the pulse is random in length. That is only one idea. Others involve inductors and diodes, capacitors, etc. You can build a circuit that simulates the action of "strange attractors" and produces a very nice distribution of random values. Or use the white noise circuit about with a sample and hold, and a fixed rate clock. At fixed intervals, a reading is taken and spit out. Now you have random voltage levels at a known interval.
Cheers!
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