[sdiy] Digital noise sources

[Ken Stone]

Elektor circuits used to make a huge diode gate to deal with the detection
of the illegal state. It is much easier to use a decoupling capacitor in the
feedback loop with a pull-down/pullup resistor to the opposite level to the
illegal one. E.g. if the register starts spitting out all 0s, the pullup
resistor will charge the cap, putting 1s on the input, restarting the sequence.

Ken


>On Fri, Jun 13, 2008 at 06:53:27PM +0200, Louis van Dompselaar wrote:
>> I always thought that the reset circuit would keep the input 0 or 1 for
>> a random-ish length.
>
>Doh!  Yes of course, the reset circuits job is to do exactly what I was
>thinking of.  I guess its highly probable that the circuit would load the
>same amount of startup data at powerup and the stream would be predictable
>which wouldn't hopefully be audibly noticable.
>
>I guess the only way to get "more random" would be to use something that
>started up in an unpredictable state like a BBDs, but even that would be
>predictable in that you'd be depending on cap leakage, or maybe using a
>noise transistor/diode with a tight filter to occasionally pop a bit into
>the the digital register.
>
>Ah well, pure random doesn't seem to matter in this case anyway and thats
>what I was pondering.
>
>Thanks.
>
>-- 
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_______________________________________________________________________
Ken Stone   sasami at hotkey.net.au
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