Arduino Pseudo-Random White Noise Source

Random_Time.ino

// Quick test for random bit generation timing
// Ed Nisley KE4ZNU - 2017-10-25
// Observe output bit on an oscilloscope

// LFSR info https://en.wikipedia.org/wiki/Linear-feedback_shift_register
//  This code uses the Galois implementation

// Coefficients from https://users.ece.cmu.edu/~koopman/lfsr/index.html

#define PIN_RND 13

#include <Entropy.h>

uint32_t Rnd;
byte LowBit;

void setup() {

  Serial.begin(57600);
  Serial.println("Random bit timing");
  Serial.println("Ed Nisley KE4ZNU - 2017-10-25");

  Entropy.initialize();

  pinMode(PIN_RND,OUTPUT);

  uint32_t Seed = Entropy.random();

  Serial.print("Seed: ");
  Serial.println(Seed,HEX);

  randomSeed(Seed);

  do {
    Rnd = random();
  } while (!Rnd);                       // get nonzero initial value

}

void loop() {

//  digitalWrite(PIN_RND,Rnd & 1);      // about 55 us/bit
//  Rnd = random();

  LowBit = Rnd & 1;
  digitalWrite(PIN_RND,LowBit);         // about 6 us/bit

  Rnd >>= 1;
  Rnd ^= LowBit ? 0x80000057ul : 0ul;

}

More details on my blog at http://wp.me/poZKh-78y