Use pin for both input and output?

Projects Programming
109

Which means you don't understand the problem.

If you would just bother to load and run the code below and push reset to your heart's content, you would see the problem.

// saved-random-seed-example
// by Aarg on Arduino Programming Forum

// maintains a rotating seed value in EEPROM to improve randomness at start up

#include <EEPROM.h>
const int SEED_ADDR = 0;

void setup() {
  while (not Serial);
  Serial.begin(115200);

  Serial.print("Program started, random using default seed value: ");
  Serial.println(random(2147483647));
  init_random_seed();
  Serial.print("random using  stored seed value: ");
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
  Serial.println(random(2147483647));
}

void loop() {
}

void init_random_seed()
{
  long seed;
  // obtain stored seed value and apply it:
  EEPROM.get(SEED_ADDR, seed);
  randomSeed(seed);
  // store a random seed for the next start up:
  EEPROM.put( SEED_ADDR, random(1, 2147483647) ); // greatest positive value of a 'long' type
}

For everyone else, this is the reliable but not very sexy way to seed random. The current version is here.