[sdiy] Simplest random source

[Seb Francis]

Hi All,

Thanks for the replies.  It seems fairly universal that analog noise is generated by taking the noise of a transistor or zener diode and amplifying it a lot, optionally with freqency shaping.

>From what I've seen, the ways of getting the required gain are:
2-3 transistors + 4-6 resistors + 1-2 caps
or
1-2 opamps + 2-4 resistors + 1 cap

The first way is probably the smallest if resistors are small or mounted sticking up.  But unfortunatly I probably don't even have space for that.

Steve Ridley also pointed out that a S&H of analog noise is much more a gausian distribution than an even one, and although it's possible to make a more even random signal in analog, this uses even more components.

So I guess it's software after all.  I've been having quite a bit of success with bitshifts+xors, getting really random 16bit numbers which don't repeat for 65535 cycles, and using about 50 instructions to generate each number.  This is getting pretty near an acceptable amount of CPU time .. so with a bit more tweaking...

I'll post the final algorithm in case it's of use to someone.

Seb