[sdiy] AVR/ARDUINO psuedo random noise?

[Magnus Danielson]

On 02/16/2011 04:18 PM, dan snazelle wrote:
> I am looking for advice or example code on how one might use the Arduino/AVR32 as really long shift register for digital noise.?
>
> i would think it could be done, using one input for clock and another input for data and using software XORS?

No input, but an output.

Here is a quick-hack which compiles but I haven't tested it:

#define NOISE 13
long state;

void setup ()
{
   // Enable the noise output pin
   pinMode (NOISE, OUTPUT);

   // Init noise state
   state = 1;
}

void loop ()
{
   if (state >> 31)
   {
     state ^= 0x400003;
     digitalWrite(NOISE, HIGH);
   }
   else
     digitalWrite(NOISE, LOW);
   state <<= 1;
}

Using the table entry for 32 bits in
http://home1.gte.net/res0658s/electronics/LFSRtaps.html

The trick here is to xor the output but backwards, which is an 
alternative approach that can be used. I could have fluked the feedback 
vector, so that may require trimming, but at least I show the code 
principle.

Cheers,
Magnus