// Arduino 2 - Counter with Frequency Calculation
int pulsePin = 2;  // Input pin connected to pulse generator
int pulsePin2 = 9; // Output pin for pulse
volatile int pulseCount = 0;  // Volatile variable for counting pulses
unsigned long lastPulseTime = 0;  // Time of the last pulse
unsigned long pulseInterval = 0;  // Time interval between pulses
float frequency = 0;  // Frequency calculation (Hz)

void setup() {
  pinMode(pulsePin, INPUT);  // Set pulse pin as input
  pinMode(pulsePin2, OUTPUT);  // Set pulse pin as output
  attachInterrupt(digitalPinToInterrupt(pulsePin), countPulse, RISING);  // Interrupt on rising edge
  Serial.begin(9600);  // Initialize Serial Monitor
}

void loop() {
  // Generate a pulse
  digitalWrite(pulsePin2, HIGH);  // Send a pulse
  delayMicroseconds(50);  // Pulse width of 1 microsecond
  digitalWrite(pulsePin2, LOW);   // End the pulse
  delayMicroseconds(50);  // Wait for 1 microsecond before next pulse

  // Print pulse count and frequency every second
  static unsigned long lastMillis = 0;
  if (millis() - lastMillis >= 1000) {
    lastMillis = millis();
    Serial.print("Pulse Count: ");
    Serial.println(pulseCount);  // Print the number of pulses detected in the last second

    // Calculate the frequency
    if (pulseCount > 1) {  // Ensure at least two pulses have been counted
      // To avoid issues with millis() overflow, we use the difference directly
      pulseInterval = millis() - lastPulseTime;  // Time between the last two pulses
      if (pulseInterval > 0) {  // Ensure the pulse interval is positive
        frequency = 1000.0 / pulseInterval;  // Calculate frequency in Hz
        Serial.print("Frequency: ");
        Serial.print(frequency);  // Print the frequency in Hz
        Serial.println(" Hz");
      } else {
        Serial.println("Frequency: Invalid interval");
      }
    } else {
      Serial.println("Frequency: Not enough pulses");
    }

    pulseCount = 0;  // Reset pulse count for the next second
  }
}

void countPulse() {
  pulseCount++;  // Increment pulse count on each pulse detected
  lastPulseTime = millis();  // Update last pulse time
}