Programming Help with a Flow Sensor and Case Statements


I am new to working with interrupts and frequency based sensors. I have a flow meter and some code, from DIY Hacking’s Website. In my project, I need it so that an LED pin continues lighting up until certain amount of water has flown.

How would I do something like this.


The code to reading the flow sensor is below:

byte statusLed    = 13;

byte sensorInterrupt = 0;  // 0 = digital pin 2

byte sensorPin       = 2;

// The hall-effect flow sensor outputs approximately 4.5 pulses per second per

// litre/minute of flow.

float calibrationFactor = 4.5;

volatile byte pulseCount;  

float flowRate;

unsigned int flowMilliLitres;

unsigned long totalMilliLitres;

unsigned long oldTime;

void setup()




  pinMode(statusLed, OUTPUT);

  digitalWrite(statusLed, HIGH);  


  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 (totalMilliLitres < 250){

   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

    // Print the cumulative total of litres flowed since starting

    Serial.print("Output Liquid Quantity: ");        

    Serial.print(totalMilliLitres);// Print tab space

    // 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);




Insterrupt Service Routine


void pulseCounter()


  // Increment the pulse counter


  pulseCount        = 0;

  flowRate          = 0.0

These values are already zero.

Why so



premudeshi: I need it so that an LED pin continues lighting up until certain amount of water has flown.

The code is a bloody insult but, without bothering to look at it in detail, it appears to be for determining flow RATE, while your objective is to determine flow QUANTITY. To do that, you don't need all those calcs and interrupt stuff, because time is not a factor. You just need to count pulses and divide by 4.5