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(fwd) Noise diodes
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From: [email protected] (Richard A. O'Keefe)
Newsgroups: sci.electronics,sci.math.consult
Subject: Noise diodes
Date: 21 Jul 1994 18:03:24 +1000
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 35
Message-ID: <[email protected]>
NNTP-Posting-Host: goanna.cs.rmit.oz.au
NNTP-Posting-User: ok
Keywords: rng
Some people I'm working with have built a machine to generate "real"
random numbers, using a BC546 transistor as an avalanche mode noise
diode (12V Vcc). The noise output is supposedly 100mV peak. That's
then fed into an LM311 comparator, to generate 0/1 signals. This is
then fed to a divide-by-2 counter. When their CPU wants a random
number, it samples the output of the divide-by-2 counter eight times
at 6.25kbit/sec.
They did collect a bunch of samples from this, and claim that successive
samples did seem to be uncorrelated, but there seemed to be a slight bias
in favour of 0 bits. However, they say the test results have been lost.
I don't really understand how the output of a divide-by-two counter can
be biassed this way
(free-running biassed random 0s and 1s) ->
(divide by 2) ->
(sample at regular intervals) ->
(take 8 consecutive samples as one random number)
They don't need to produce random numbers at a very high rate (a couple
of hundred a second is more than enough for their application).
I have a faint memory that there are several problems with generating
random numbers from noise diodes, but I can't remember what any of them
are. The requirement is for
- independent
- equidistributed
- random 0..255 integers
- which remain so throughout a 0 to 40 degree Celsius range
If there is a standard way to get something like this, I'd like to hear
about it. If there is a standard set of problems I should know about
and check for, that'd be great.
--
30 million of Australia's 140 million sheep
suffer from some form of baldness. -- Weekly Times.