[sdiy] Fun with LFSRs and such

[Matthew Smith]

Quoth Colin Hinz at 25/03/12 05:53...
...
> But it becomes more interesting when it's used as a LF gate, and gets
> even more interesting when the taps are chosen with "good" noise
> not in mind. Long sequences of '1' or '0' intermingled with bursts
> of more random behaviour = golden!
>
> So I present to you a circuit. I've got an LFSR which gates a NAND
> synth. Have a look at the schematic:

Very interesting indeed.

Being that way inclined, I find myself looking at implementing the logic 
in a CPLD (or even a small FLASH-equipped FPGA, which I can get for 
about $14.)

One thing I haven't come across before is the concept of a NAND synth 
and now wonder if, that part of it too, could not be implemented in 
programmable logic. I can't see any logical (ha!) reason why not, but 
others may see what I'm missing.

I certainly like the idea of switchable taps, and am very much inclined 
to do a last-minute change on the noise-generator that I was going to 
implement so that it could either run in the "traditional" way, or be 
switched in the manner of Colin's.

To save me grabbing my phone and firing up the 555 calculator (part of 
Electrodroid, for any Android users, think there may be an iPhone 
version now,) what's the frequency range of the 555?  I know way back 
when (last year) when we were talking on this subject, someone said that 
dropping the frequency below a certain point would turn the noise output 
into something more reminiscent of Space Invaders, which somewhat 
appealed to me ;-)

Seeing as how I've just got some XC95144 prototype PCBs back from 
fabrication, this seems rather timely.

Cheers

M


-- 
Matthew Smith

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