/*
  Flow Sensor Counter Meter FS300A G3/4
  Flow rate :   1-60L/min
  Flow Pulse:   508 pulse / Liter
*/
#define  FS300A_PULSE     508         // PULSE / LITER
#define  FS300A_FLOW_RATE 60          // LITER / MINUTE
const float factor = 60.0F / 508.0F;  // FS300A_FLOW_RATE / FS300A_PULSE

#define interruptPin 2

uint16_t pulse;
uint16_t count;

float frequency;
float flowRate;

bool busy;

void setup() {
  Serial.begin(115200);

  pinMode(interruptPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(interruptPin), FlowInterrupt, CHANGE);
}

void loop() {
  Frequency();
}

void FlowInterrupt() {
  busy = true;
  pulse++;
  busy = false;
}

void Frequency() {
  static unsigned long startTime;
  if (micros() - startTime < 1000000UL ) return;   // 1000 milliseconds Interval
  startTime = micros();

  while (busy) {};

  uint8_t sreg = SREG;
  cli();
  count = pulse;
  pulse = 0;
  SREG = sreg;

  frequency = count / 2.0f;
  flowRate = frequency * factor;

  PlotInfo();
}

void PlotInfo() {
  Serial.print("Freq.:= " + String(frequency, 2) + " Hz");
  Serial.println(", FLow:= " + String(flowRate, 3) + " L/min");
}