the pulse counter is reporting almost half the number it should report.

flow_controller.ino

@@ -4,30 +4,69 @@ Servo myServo;           // Create a Servo object
 const int servoPin = 10; // D10 is OC1B on Pro Mini
 const int ledPin = 13;
 const int analogPin = A0;
+const int SensorPin = 2;
+
+volatile uint16_t pulses = 0,ppm = 0; //pulse per minute
+
+
+// Interrupt Service Routine (ISR)
+void INT0_ISR() {
+  pulses++;
+}
+
+void setup_timer() {
+
+  // Stop Timer2
+  TCCR2A = 0;
+  TCCR2B = 0;
+  TCNT2 = 0;
+  // Set compare match value for 100ms
+  // Clock = 16 MHz, Prescaler = 1024
+  // Tick = 16,000,000 / 1024 = 15,625 ticks/sec
+  // 100ms = 0.1s → 0.1 * 15625 = 1562.5 ticks
+  // Since Timer2 is 8-bit, we can't reach 1562 in one cycle.
+  // So we will count multiple compare matches.
+  OCR2A = 50; // Compare match every ~16ms (250 counts at 1024 prescaler)
+  // CTC mode
+  TCCR2A |= (1 << WGM21);
+  // Prescaler = 1024
+  TCCR2B |= (1 << CS22) | (1 << CS21) | (1 << CS20);
+  // Enable compare match interrupt
+  TIMSK2 |= (1 << OCIE2A);
+  // Enable global interrupts
+  sei();
+}
 
 void setup() {
   pinMode(ledPin, OUTPUT);       
   Serial.begin(115200);            // Initialize Serial
   myServo.attach(servoPin);      // Attach servo to pin 10
+  
+  attachInterrupt(digitalPinToInterrupt(SensorPin), INT0_ISR, FALLING);
+  setup_timer();
 }
 
 void loop() {
   int analogValue = analogRead(analogPin); // Read from A0 (0–1023)
   int angle = map(analogValue, 0, 1023, 0, 180); // Map to 0–180 degrees
+  Serial.print("pulses: ");
+  Serial.println(pulses);
 
   myServo.write(angle);  // Set servo angle
 
-  digitalWrite(ledPin, HIGH);
-  // Serial.print("LED ON - Analog: ");
-  // Serial.print(analogValue);
-  // Serial.print(" | Angle: ");
-  // Serial.println(angle);
-  delay(10);
-
-  digitalWrite(ledPin, LOW);
-  // Serial.print("LED OFF - Analog: ");
-  // Serial.print(analogValue);
-  // Serial.print(" | Angle: ");
-  // Serial.println(angle);
-  delay(10);
+  delay(1000);
+}
+
+
+ISR(TIMER2_COMPA_vect) {
+  static uint16_t ticks = 0;
+  static bool ledState = false;
+  ticks++;
+  if (ticks >= 150) { // 150 => 1s
+    ticks = 0;
+    ledState = !ledState;
+    ppm = pulses;
+    pulses = 0;
+    digitalWrite(ledPin, ledState);
+  }
 }