[sdiy] AVR/ARDUINO psuedo random noise?

[dan snazelle]

On Feb 16, 2011, at 11:46 AM, Magnus Danielson wrote:

> 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
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XOR The output but backwards? not quite sure what you mean. I will go try this out!

thanks