Measure flow rates using Particle Photon

byte statusLed = D1;
byte sensorInterrupt = D2;
byte sensorPin = D2;
 
// ~4.5 pulses/sec per L/min for this hall-effect meter
float calibrationFactor = 4.5;
 
volatile byte pulseCount;
float flowRate;
unsigned int flowMilliLitres;
unsigned long totalMilliLitres;
unsigned long oldTime;
 
void setup() {
  Serial.begin(38400);
 
  pinMode(statusLed, OUTPUT);
  digitalWrite(statusLed, HIGH); // active-low LED
 
  pinMode(sensorPin, INPUT);
  digitalWrite(sensorPin, HIGH);
 
  pulseCount = 0;
  flowRate = 0.0;
  flowMilliLitres = 0;
  totalMilliLitres = 0;
  oldTime = 0;
 
  attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
}
 
void loop() {
  if ((millis() - oldTime) > 1000) {
    detachInterrupt(sensorInterrupt);
 
    flowRate = ((1000.0 / (millis() - oldTime)) * pulseCount) / calibrationFactor;
    oldTime = millis();
 
    flowMilliLitres = (flowRate / 60) * 1000;
    totalMilliLitres += flowMilliLitres;
 
    unsigned int frac;
    char str[10];
    char str2[10];
 
    Serial.print("Flow rate: ");
    Serial.print(int(flowRate));
    Serial.print(".");
    frac = (flowRate - int(flowRate)) * 10;
    Serial.print(frac, DEC);
    Serial.print(" L/min");
 
    Serial.print("  Current Liquid Flowing: ");
    Serial.print(flowMilliLitres);
    Serial.print(" mL/Sec");
    sprintf(str, "%d", flowMilliLitres);
    Particle.publish("FlowRatesmlPerSec", str);
 
    Serial.print("  Output Liquid Quantity: ");
    Serial.print(totalMilliLitres);
    Serial.println(" mL");
    sprintf(str2, "%d", totalMilliLitres);
    Particle.publish("totalFlowInML", str2);
 
    pulseCount = 0;
    attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
  }
}
 
void pulseCounter() {
  pulseCount++;
}