Path: bga.com!news.sprintlink.net!news.onramp.net!convex!cs.utexas.edu!swrinde!ihnp4.ucsd.edu!agate!msuinfo!harbinger.cc.monash.edu.au!aggedor.rmit.EDU.AU!goanna.cs.rmit.oz.au!not-for-mail From: ok@goanna.cs.rmit.oz.au (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: <30la4c$bng@goanna.cs.rmit.oz.au> 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.