[sdiy] Simplest random source

[Seb Francis]

Hi Magnus,

I couldn't find too much in the archives ..
http://www.buchi.de/sdiy/Search1.ASP?914

And a search on google for PRBS didn't help me too much either.  But I am interested if you can give me a link to a schematic or algorithm.

Magnus Danielson wrote:

> If you look way back in time, you will be able to find a thread about random
> generators and there I posted PRBS generator polynoms all the way up to 64 bits
> of length. You will also find me arguing for the use of longer polynomial
> lengths. Inside a PIC, AVR or anything like it, there is no excuse not to use
> up the hardware better and go for a long polynomial.

The question for me would be how many instructions does it take to get a 16bit 'random-enough' number.


> You get both cycletimes
> beyond lifetime of the apparatous and thick noise-spectrum, which you do want
> That comes hand-in-hand when you go for the longer polynoms. a 64 bit polynom
> requires only 8 byte of storage and we're still only talking one or two XOR
> gates, so processing is still fairly simple.
>

The previously posted algorithm should be an exact replica of this circuit:
http://www.analog-synth.de/synths/mod2/trigdiv/dig_noise.gif
Now this looks very much to me like a long shift register with some XOR taps .. could it be a similar thing?

Seb