// Optical Speed Sensor
// Board: Arduino UNO
// Count pulses from the optical slot sensor.

const int SENSOR_PIN = 2;
volatile unsigned long pulseCount = 0;
unsigned long lastTime = 0;

void countPulse() {
  pulseCount++;
}

void setup() {
  Serial.begin(9600);
  pinMode(SENSOR_PIN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(SENSOR_PIN), countPulse, FALLING);
}

void loop() {
  if (millis() - lastTime >= 1000) {
    noInterrupts();
    unsigned long count = pulseCount;
    pulseCount = 0;
    interrupts();

    Serial.print("Pulses per second: ");
    Serial.println(count);
    lastTime = millis();
  }
}