geiger_external_arduino.ino

#define LOG_PERIOD 20000 //Logging period in milliseconds
#define MINUTE_PERIOD 60000

volatile unsigned long counts = 0;                       // Tube events
unsigned long cpm = 0;                                   // CPM
unsigned long previousMillis;                            // Time measurement
const int inputPin = 2;

void ISR_impulse() { // Captures count of events from Geiger counter board
  counts++;
  Serial.println("click");
}

void setup() {
  Serial.begin(9600);

  pinMode(inputPin, INPUT); 
  interrupts();
  attachInterrupt(digitalPinToInterrupt(inputPin), ISR_impulse, RISING); // Define interrupt on falling edge
}

void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis > LOG_PERIOD) {
    previousMillis = currentMillis;
    cpm = counts * MINUTE_PERIOD / LOG_PERIOD;

    Serial.println(String(cpm) + " cpm");
    counts = 0;
  }
}