Flow meter and relays

Hi everyone

I need some help with code.

I am new to arduino

I have a flow meter
Hall Water Flow Sensor Flowmeter Water Control

and a relay board
Eight channel 5V DC Relay Module

I need a code where I press a button and the relay must open and as soon as the flow meter reach 500ml the relay must close again.

Please help

I need some help with code.

I need a code where ...

Please help

Help in this forum seems to mean that you have a go first, ie post what you have so far, and then ask for help on specifics.

I have a flow meter
Hall Water Flow Sensor Flowmeter Water Control

and a relay board
Eight channel 5V DC Relay Module

You'll probably need to provide some more details about those: make, model, link to datasheets

I am new to arduino

Have you done these tutorials?

Some hints.
Pressing the button latches the relay, presumably energised, to the ON state. It stays ON when you release the button. Look at states and toggling push-buttons. Statechange in Arduino examples always works well.
You need to look at de-bouncing as well.
In your code, you read the flow rate by counting pulses and convert that to flow - you start off talking about flow, then talk about volume. 500ml is a volume not a flow - 500ml per second is a flow.
So get that straight first. If you are measuring a volume, you don't need a flow-meter.
So are you monitoring the flow and turning the relay off when it goes over 500ml per ?? or do you want to turn it off when you get 500ml volume?
Either way, you use an IF statement to compare what you are measuring against a fixed value and make a decision based on the two values. So, if flow or volume is greater or equal to 500, turn off, if not, don't turn off.
If this is your first project, you are going to have to get familiar with some basics.
Having said that, what you want to do, flow or volume, is reasonably straightforward and ideally suited to an MCU.
Another hint, have a look at thermostat examples.
I don't think anyone is going to write the code for you, though. If you try a few things and they don't work, put your efforts here then you might get some more detailed help


It will also be a great help to me if someone has such a program.

so pleas help os!

or if you just have something similar

It will also be a great help to me if someone has such a program.

or if you just have something similar

You will also need to provide hardware details...

here is my program, but it is not, done. but it is a start

Build on basis of Liquid flow rate sensor -DIYhacking.com Arvind Sanjeev

Measure the liquid/water flow rate using this code. 
Connect Vcc and Gnd of sensor to arduino, and the 
signal line to arduino digital pin 2 with a 10kOhm Resistor to 5V to get RS-Comp flow sensor to function

byte statusLed    = 5;
const int relayPin = 7;

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 = 60;// This has to be changed when in final operation to adjust to correct flow of liquid.

volatile byte pulseCount;  

float flowRate;
unsigned int flowMilliLitres;
unsigned long totalMilliLitres = 0;
int relayState = 0;
unsigned long oldTime;

void setup()
   // Initialize a serial connection for reporting values to the host. The measured flow will be displayed in the arduino Serial Monitor ( /Tools/Serial monitor )
 // Set up the status LED line as an output
 pinMode(statusLed, OUTPUT);
 digitalWrite(statusLed, HIGH);  // We have an active-low LED attached
 pinMode(sensorPin, INPUT);
 digitalWrite(sensorPin, HIGH);
 pinMode(relayState, INPUT);

 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);

//Main program loop

void loop()
 // Detect input pulse from external to start flow measurement
//  if(digitalRead(InputPin) == HIGH)
// {
//    EnableFlow = 1;
//  }

 // Make flow measurement until triggered
//  if (EnableFLow)
//  {
//    digitalWrite(statusLed, HIGH);

//    ValveOpen();
//    flow = MeasureFlow();

//    if(flow > TriggerFlow)
//    {
//      ValveClose();
     // Set Pin High ?
//      digitalWrite(statusLed, LOW);
//      EnableFlow = 0;

     // Reset Flow Measurement
//      flow = 0;
//    }
//  }

relayState = digitalRead(relayPin); // read state of PIN4 

if (relayState == HIGH) // if button is not pressed run - This must be changed to HIGH in final operation


 if ((totalMilliLitres < 50))// define amout on liquid to flow before switch off relay
   if((millis() - oldTime) > 500)    // Only process counters once per second //measureflow
     // 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. A fixed number amy be added to offset the missing flow data here.
     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;
     // All Print functions may be removed from final itteration to speed up operations, Just added for debugging purposes. 
     // 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(".");             // Print the decimal point
     // Determine the fractional part. The 10 multiplier gives us 1 decimal place.
     frac = (flowRate - int(flowRate)) * 10;
     Serial.print(frac, DEC) ;      // Print the fractional part of the variable
     // Print the number of litres flowed in this second
     Serial.print("  Current Liquid Flowing: ");             // Output separator

     // Print the cumulative total of litres flowed since starting
     Serial.print("  Output Liquid Quantity: ");             // Output separator

     // 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);

   digitalWrite(statusLed, LOW); //Power off to relay 
   totalMilliLitres = 0;
   delay(3000);//wait 3 sec;
   digitalWrite(statusLed, HIGH);//reset relay switch to run again
  relayState = LOW; // setting the relay state low and resetting the code. This will have to be removed in final implementation

Interrupt Service Routine

void pulseCounter()
 // Increment the pulse counter

Please fix your use of code tags, please provide those datasheet links...

// The hall-effect flow sensor outputs approximately 4.5 pulses per second per
// litre/minute of flow.

For that kind of slow signals you don't need to bother with interrupts.

Here is a very simple routine I use. If your information is accurate your meter is working the same way pulses/volume. Do a dimensional analysis. This bit of code is just edge detection with a time measurement between pulses. Please see "State Change Detection" in the Examples for further information. If you need faster you can use micros(), and/or interrupts as needed. As the previous reply noted you really don't need to.

  Flow meter for well monitoring. Meter is pulse per unit volume type.
  Created 2019
  A. J. Lindfors
//set the pins
const byte inFlow = 2;  // pin for the flow signal input
//integer variables for controls
int stateNew = LOW; //initialize
int stateOld = LOW; //initialize
int pulseTime;
//timing and calculation variables
unsigned long startTime, stopTime, pulseFlow;
float totalFlow,  flowRate, timeInterval;

void setup() {
  //set the pins
  pinMode(inFlow, INPUT);
  //serial set-up

void loop() {
  stateNew = digitalRead(inFlow);
  if (stateNew != stateOld) {
    if (stateNew == HIGH) {
      pulseFlow++; //increment a counter for back checking
      startTime = millis();
      totalFlow = 0.10 + totalFlow; //varies by meter
      timeInterval = startTime - stopTime;
      flowRate = 1.667 / timeInterval; //varies by meter
      // do any checks here

      //output in CSV form
    stateOld = stateNew;
    stopTime = startTime;