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Water Flow sensor is basically used to take a note of how much water has been transferred from one area to the other. Water flow sensor consists of a plastic valve body, a water rotor and a hall-effect sensor. When water flows through the rotor, the rotor start rolling after feeling the pressure. Its speed changes with different rate of flow. The hall-effect sensor outputs the corresponding pulse signal.


Nowadays water flow sensor is used in wide variety of areas. Some common Examples are: Water Management, Mining and Extracting, Agriculture, etc.

Project for Reference:


byte statusLed    = 13;
byte sensorInterrupt = 0;
byte sensorPin       = 2;

float calibrationFactor = 4.5;
volatile byte pulseCount;
float flowRate;
unsigned int flowMilliLitres;
unsigned long totalMilliLitres;
unsigned long oldTime;

void setup()
  Serial.begin(9600);  // Initialize a serial connection for reporting values to the host
  pinMode(statusLed, OUTPUT);  // Set up the status LED line as an output
  digitalWrite(statusLed, HIGH);  // We have an active-low LED attached

  pinMode(sensorPin, INPUT);
  digitalWrite(sensorPin, HIGH);

  pulseCount        = 0;
  flowRate          = 0.0;
  flowMilliLitres   = 0;
  totalMilliLitres  = 0;
  oldTime           = 0;

  // The Hall-effect sensor is connected to pin 2 which uses interrupt 0.
  // Configured to trigger on a FALLING state change (transition from HIGH
  // state to LOW state)
  attachInterrupt(sensorInterrupt, pulseCounter, FALLING);

void loop()
  if ((millis() - oldTime) > 1000)   // Only process counters once per second
    // Disable the interrupt while calculating flow rate and sending the value to
    // the host

    // Because this loop may not complete in exactly 1 second intervals we calculate
    // the number of milliseconds that have passed since the last execution and use
    // that to scale the output. We also apply the calibrationFactor to scale the output
    // based on the number of pulses per second per units of measure (litres/minute in
    // this case) coming from the sensor.
    flowRate = ((1000.0 / (millis() - oldTime)) * pulseCount) / calibrationFactor;

    // Note the time this processing pass was executed. Note that because we've
    // disabled interrupts the millis() function won't actually be incrementing right
    // at this point, but it will still return the value it was set to just before
    // interrupts went away.
    oldTime = millis();

    // Divide the flow rate in litres/minute by 60 to determine how many litres have
    // passed through the sensor in this 1 second interval, then multiply by 1000 to
    // convert to millilitres.
    flowMilliLitres = (flowRate / 60) * 1000;

    // Add the millilitres passed in this second to the cumulative total
    totalMilliLitres += flowMilliLitres;

    unsigned int frac;

    // Print the flow rate for this second in litres / minute
    Serial.print("Flow rate: ");
    Serial.print(int(flowRate));  // Print the integer part of the variable
    Serial.print("\t"); 		  // Print tab space

    // Print the cumulative total of litres flowed since starting
    Serial.print("Output Liquid Quantity: ");
    Serial.print("\t"); 		  // Print tab space
    Serial.print(totalMilliLitres / 1000);

    // Reset the pulse counter so we can start incrementing again
    pulseCount = 0;

    // Enable the interrupt again now that we've finished sending output
    attachInterrupt(sensorInterrupt, pulseCounter, FALLING);

void pulseCounter()
  // Increment the pulse counter