Hall Effect [Water] Flow Sensor

/*
	Water Flow Sensor Test Sketch
 */

#include <Wire.h>
#include <SSD1306Wire.h>        // OLED Display
 
#define I2C_SCL D1 // GPIO5
#define I2C_SDA D2 // GPIO4
#define SENSOR  D3 // GPIO0

// OLED Display Settings
const int Display_I2C_Address = 0x3c;
SSD1306Wire display(Display_I2C_Address, I2C_SDA, I2C_SCL);

long currentMillis = 0;
long previousMillis = 0;
long reportStartMillis = 0;
long reportEndMillis = 0;
int timeInterval = 10000;  // In milliseconds
// float calibrationFactor = 1.08;
float pulsesPerLitre = 64.8;
volatile byte pulseCounter;
byte pulseCount = 0;
byte reportPulseCount = 0;
float flowRate;
unsigned long flowMilliLitres;
unsigned int totalMilliLitres;
float flowLitres;
float totalLitres;

// General
int reportInterval = 60;  // In seconds

void IRAM_ATTR pulseMonitor()
{
  pulseCounter++;
}
 
void setup()
{
  Serial.begin(115200);
  delay(500);
  
  Serial.println("[setup] NodeMCU Water Flow Sensor Node");
  Serial.println();

  pinMode(SENSOR, INPUT_PULLUP);

// Initialise the OLED display
  display.init();
  display.flipScreenVertically();
  display.setFont(ArialMT_Plain_10);
  display.setTextAlignment(TEXT_ALIGN_LEFT);
  display.drawString(5,5,"I2C Flow Sensor");
  display.display();
 
  pulseCounter = 0;
  flowRate = 0.0;
  flowMilliLitres = 0;
  totalMilliLitres = 0;
  previousMillis = 0;
 
  attachInterrupt(digitalPinToInterrupt(SENSOR), pulseMonitor, FALLING);

  Serial.println("[setup] Set-up Complete");
  Serial.println();
}
 
void loop()
{
  currentMillis = millis();
  if (currentMillis - previousMillis > timeInterval) 
  {
    
    pulseCount = pulseCounter;
    reportPulseCount = reportPulseCount + pulseCount;
 
    // Because this loop may not complete in precise timeIntervals 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() - previousMillis)) * pulse1Sec) / calibrationFactor;
//    Serial.print("[loop] pulseCount: ");
//    Serial.println(pulseCount);
//    Serial.print("[loop] pulsesPerLitre: ");
//    Serial.println(pulsesPerLitre);
    timeInterval = millis() - previousMillis;
    flowRate = pulseCount/(((float)timeInterval / 60000) * pulsesPerLitre);

//    Serial.print("[loop] flowRate: ");
//    Serial.println((float)flowRate,2);

    previousMillis = millis();
    pulseCounter = 0;
 
    // Divide the flow rate in litres/minute by (60/timeInterval) to determine how many litres have
    // passed through the sensor in this timeInterval, then multiply by 1000 to
    // convert to millilitres.
    flowLitres = (flowRate / (60000 / (float)timeInterval));
    flowMilliLitres = flowLitres * 1000;
 
    // Add the millilitres passed in this second to the cumulative total
    totalMilliLitres += flowMilliLitres;
    totalLitres += flowLitres;
    
    // Print the flow rate for this second in litres / minute
    Serial.print("Flow rate: ");
    Serial.print(float(flowRate));  // Print the integer part of the variable
    Serial.print(" L/min");
    Serial.print("\t");       // Print tab space
 
    display.clear();
    
    display.drawString(10,0,"Water Flow Meter");
    display.display();
    
    display.setFont(ArialMT_Plain_24);
    display.drawString(0,15,"R:");
    display.drawString(30,15,String(float(flowRate)));

    display.setFont(ArialMT_Plain_10);
    display.drawString(110,28,"L/M");
 
    // Print the cumulative total of litres flowed since starting
    Serial.print("Output Liquid Quantity: ");
    Serial.print(totalMilliLitres);
    Serial.print(" mL / ");
    Serial.print(totalLitres);
    Serial.println(" L");
 
    display.setFont(ArialMT_Plain_24);
    display.drawString(0,40,"V:");
    display.drawString(30,40,String(totalLitres));
    display.setFont(ArialMT_Plain_10);
    display.drawString(110,53,"L");
    display.display();

  }
}