Using two flow sensors connected to one Arduino.

Using Arduino Sensors
8

fiddled a bit with your code:

  • use #define for those vars that are not changeable
  • made 2 different IRQ's one for counting the IN pulses and one for counting the out pulses
  • changed some var names to reflect what they meant like litersperminute
  • use a copy of millis() in the if block as millis() might change during the block (accuracy)
  • probably screwed up the math but you should be able to fix that relative easily
  • made some vars local instead of global (reduce scope)

have a look and give it a try (not tested as I don't have an I2CLCD nearby :slight_smile:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,16, 2);

// as these are const one better use #defines
#define IRQ_A 0
#define IRQ_B 1
#define PIN_A 2
#define PIN_B 3

// a separate counter per channel
volatile unsigned long countIN = 0;
volatile unsigned long countOUT = 0;
unsigned long oldTime  = 0;

void setup()
{
  lcd.begin(16, 2);

  Serial.begin(9600);

  pinMode(PIN_A, INPUT);
  pinMode(PIN_B, INPUT);
  digitalWrite(PIN_A, HIGH);
  digitalWrite(PIN_B, HIGH);

  attachInterrupt(IRQ_A, CounterIN, FALLING);
  attachInterrupt(IRQ_B, CounterOUT, FALLING);
}

void loop()
{
  // use a var for value of millis, as it might change in the if .... block
  // due to slow serial prints
  unsigned long now = millis();
  if((now - oldTime > 1000))
  {
    unsigned long duration = now - oldTime;
    oldTime = now;

    // use names that indicate the unit!
    // don't know if all math is correct anymore
    // 8500 pulses per liter?
    float liters = (countIN - countOUT) * 0.000117647; // faster than divide by 8500.0
    float litersPerMinute = (1000 * liters)/duration / 60; // optimized 16.66667*liters/duration

    Serial.print(duration);
    Serial.print(",");  // separate by comma's so you can copy output to Excel easily.
    Serial.println(litersPerMinute, 3);     // print a float with three decimals

    int LPM = litersPerMinute;               // implicit conversion to int
    int frac = (litersPerMinute-LPM)*10;
    lcd.setCursor(0, 0);
    lcd.print("Flow L/min: ");
    lcd.print(LPM);  
    lcd.print(".");    
    lcd.print(frac);  
    lcd.print(" ");
  }
}

void CounterIN()
{
  countIN++;
}

void CounterOUT()
{
  countOUT++;
}