Flow meter sensor with M2Som

Hardware
1

hi, I am trying to use a simple flow meter with the m2 som, adapting code form Arduino. I just get 0s when I flash to the Particle board, not sure if there is something wrong with the way the interrupts are written, or if there is a bigger issue. I looked at other related posts with flow sensor issues but they were all for Core or Spark and the code does not compile on the m2som. Thanks!

type or paste code /*
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.
 
 */

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()
{
  
  // Initialize a serial connection for reporting values to the host
  Serial.begin(9600);
   
  // 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);

  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()
{
   
   if((millis() - oldTime) > 1000)    // Only process counters once per second
  { 
    // Disable the interrupt while calculating flow rate and sending the value to
    // the host
    detachInterrupt(sensorInterrupt);
        
    // 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("L/min");
    Serial.print("\t"); 		  // Print tab space

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

    // 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++;
}here
2

What is or is not working?

You also shouldn't detach the reattach the interrupt handler when processing it. There are better ways to prevent simultaneous access.

In any case, the solution kind of depends on what kind of flow meter you have:

Slow click rate

If you have a flow meter that emits a click every few seconds, such a household water meter with an external sensor contact, you mainly want to make sure the signal is debounced, because errant detection will cause significant errors.

In this case, I just remember the millis() value in a global variable from the ISR. Examine the value from loop to determine if you recently got a click.

Fast click rate

If you have a turbine style flow meter that emits many clicks per second, an errant click won't cause a significant error, and the large number of clicks means the handling from an interrupt is required.

The first thing is to use atomic variables to store the value. This is my declaration:

// Required header
#include <atomic>

// Global (could be a class member instead)
std::atomic_uint32_t flowCountAtomic;

void flowISR(void) {
    flowCountAtomic.fetch_add(1, std::memory_order_relaxed);
}

To read the value from loop(), you use this, which safely gets the old value and sets it to zero:

uint32_t lastValue = flowCountAtomic.fetch_and(0, std::memory_order_relaxed);
3

It's a turbine style flow meter. I am just seeing 0 for all values where as when I run this code in Arduino I do see the flow rate and total mL.
Oddly I am seeing values now without changing anything. Is there an example that explains the atomic variable so I can understand how to adapt my code and fix the interrupts? Thanks!

4

How is it connected?

Usually the flow meter just has two wires that close for each click. You usually connect one wire to GND and the other to the digital input. Then you either add an external pull-up resistor, or set the pinMode to INPUT_PULLUP instead of INPUT.