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On Wedsday night I attended dorkbot NYC (people doing strange things with electricity) and had a chance to meet Rob Seward who made a device that may or may not detect "consciousness fields"... the device is basically a random number generator and Rob has released the how-to online... - "This generator uses avalanche noise, and is based on a design by Will Ware. Herein are instructions as to how you can use a pic chip to analyze a noise source and output random data serially. I've included circuit diagrams as well as links to instructions for fabricating your own board.
There are two types of random numbers: true and pseudo. Pseudo random numbers are created by an algorithm. The problem with this is that if someone knows what algorithm you use, it is theoretically possible predict what numbers you will create. True random number generators create sequences that are impossible to predict. They use random physical phenomenon as their source or randomness. They are used for encryption and micro psychokinesis research." - Link.
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Using a transistor to get a reverse PN noise source is clever. This is typically a zener diode application.
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In the design in the link, the 2N3904 transistor is used in zener breakdown mode. This transistor is not designed to work for extended time in this mode, and indeed the design exceeds the 2N3904 Vebo Absolute Maximum Rating. This causes a well-understood failure mechanism, where the circuit first drifts, and then fails.
The other challenge with this true random number generator is to prevent interference from periodic signals. In this circuit, the challenge is to isolate the MAX232 switching frequency. There is also periodic interference from the PIC to contend with.
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A few years back the lava lamp random number guys (yes, they really did photograph lava lamps with a webcam) came up with a simpler technique. They sample the noise off a CCD chip in a webcam. The process is explained here.
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