RC Entropy Pool - test circuit and code

RC-EntropyPool-testcode.c

// RC Entropy source...
// experimental code - NOT FOR USE IN PRODUCTION!!
// --- not proven to be anywhere close to CSPRNG nor TruRNG ---
// by Mark C (@LargeCardinal)
//
// So, a 1.2 to 1nF ceramic cap and 100Ohm resistor are placed in
// parallel across the A6 and GND pins. A fly wire from Digital
// pin 2 then goes to the A6 rail, powering the cap of 1nF and 100Ohm res
// 
// In practice, it seems we really don't need the capacitor... maybe
// we can rely on the capacitance/resistance in the ADC converter itself?!

int coin_flip(void) {
  int little_bit;
  digitalWrite(2,1);
  delay(2);
  return little_bit = (analogRead(A6) & 1);
}

int getFairBit(void) {
  while(1)
  {
    int a = coin_flip();
    if (a != coin_flip()){
      return a;
    }
  }
}

int get_rand_byte(void){
  int n=0;
  int bits = 7;
  while (bits--) {
    n<<=1; 
    n |= getFairBit();
  }
  return n;
}

void setup()
{
  // set driver pin to output:
  pinMode(2, OUTPUT);
  // start serial
  Serial.begin(9600);
  // warm up the capacitor! :P
  digitalWrite(2, 1);
  delay(200);
  digitalWrite(2, 0);
  Serial.println("init done!");
}

void loop()
{
  unsigned int rand_word, rand_byte1, rand_byte2 = 0;
  for ( int i = 0; i < 10000; i++) {
    rand_byte1 = get_rand_byte();
    Serial.print("random byte: "); Serial.println(rand_byte1, HEX);
  }
  // this is just so I can see when it's done :P 
  delay(100000);
}