an array of LEDs that turns on and off at random times (within a range)

randomLED.ino

const int numLeds = 4;
const int pins[] = {
  2, 3, 4, 5};

long t_random[numLeds];
long t_reset[numLeds];
long top_range = 2000;
long bottom_range = 100;
int previous_led_state[numLeds];
int led_state[numLeds];

void setup() {
  randomSeed(analogRead(0));
  for (int i = 0; i < numLeds; i++) {
    pinMode(pins[i], OUTPUT);
    t_random[i] = random(bottom_range, top_range);
    t_reset[i] = millis();
    previous_led_state[i] = LOW;
    led_state[i] = HIGH;
  }
}

void loop() {
  for (int i = 0; i < numLeds; i++) {
    if (millis() - t_random[i] > t_reset[i]) {
      if (previous_led_state[i] == LOW) {
        led_state[i] = LOW;
        previous_led_state[i] = HIGH;
      }
      else {
        led_state[i] = HIGH;
        previous_led_state[i] = LOW;
      }
      t_random[i] = random(bottom_range, top_range);
      t_reset[i] = millis();
    }
    digitalWrite(pins[i], led_state[i]);
  }
}