Activating LED on signal input=null

Other Hardware LEDs and Multiplexing
7

slipstick:
Please post the complete code.

I can see at least 3 conditions even in that unhelpful fragment. Which one is "this condition"?

Steve

here is the full code

#define GREEN 3
#define BLUE 6
#define WHITE 10 
#define RED 9 
#define YELLOW 11 
#define RED 5

const int ledPin = 3;
int ledState = LOW;
unsigned long previousMillis = 0;
const long interval = 1000;

byte statusLed    = 13;
byte sensorInterrupt = 0;
byte sensorPin       = 2;
float calibrationFactor = 4.5;
volatile byte pulseCount;  
float flowRate;
unsigned int flowMilliLitres;
unsigned long totalMilliLitres;
unsigned long oldTime;

void setup()
{
  
  Serial.begin(9600);
  pinMode(statusLed, OUTPUT);
  digitalWrite(statusLed, HIGH);
  pinMode(sensorPin, INPUT);
  digitalWrite(sensorPin, HIGH);
  pinMode(GREEN,OUTPUT);
  digitalWrite(GREEN,HIGH);
  digitalWrite(GREEN,LOW);
  pinMode(ledPin, OUTPUT);

  pinMode(BLUE,OUTPUT);
  digitalWrite(BLUE,HIGH);
  digitalWrite(BLUE,LOW);

  pinMode(WHITE,OUTPUT);
  digitalWrite(WHITE,HIGH);
  digitalWrite(WHITE,LOW);

  pinMode(RED,OUTPUT);
  digitalWrite(RED,HIGH);
  digitalWrite(RED,LOW);

  pinMode(YELLOW,OUTPUT);
  digitalWrite(YELLOW,HIGH);
  digitalWrite(YELLOW,LOW);

  pulseCount        = 0;
  flowRate          = 0.0;
  flowMilliLitres   = 0;
  totalMilliLitres  = 0;
  oldTime           = 0;

  
  attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
}


void loop()
{
  
   if((millis() - oldTime) > 1000)
  { 
     detachInterrupt(sensorInterrupt);
        
    flowRate = ((1000.0 / (millis() - oldTime)) * pulseCount) / calibrationFactor;
    oldTime = millis();
    flowMilliLitres = (flowRate / 60) * 1000;
    totalMilliLitres += flowMilliLitres;
    if (ledState == LOW &&((flowRate < 0.01)) (digitalWrite(GREEN,HIGH));
    {
    ledState = HIGH;
    }
    
    else digitalWrite (GREEN,LOW);
    

     if (flowRate >= 4.00) digitalWrite(BLUE,HIGH);
    else digitalWrite (BLUE,LOW);

     if (flowRate >= 12.01) digitalWrite(WHITE,HIGH);
    else digitalWrite (WHITE,LOW);

     if (flowRate >= 22.1) digitalWrite(RED,HIGH);
    else digitalWrite (RED,LOW);

     if (flowRate >= 34.1) digitalWrite(YELLOW,HIGH);
    else digitalWrite (YELLOW,LOW);
      
    unsigned int frac;
    
    
    Serial.print("Flussometro: ");
    Serial.print(int(flowRate)); 
    Serial.print("L/min");
    Serial.print("\t");       

    Serial.print("Quantita': ");        
    Serial.print(totalMilliLitres);
    Serial.println("mL"); 
    Serial.print("\t");
    
    

    
    pulseCount = 0;
    
   
    attachInterrupt(sensorInterrupt, pulseCounter, FALLING);
  }
}

void pulseCounter()
{
  pulseCount++;
}

the condition you can see in the void loop .
I just need to insert a double condition with double 'then' or 'do' to make a led blink when the flow is <0.01 (which will be a very good sign instead of just being lighted up ) , blinking is more notable
so my attempt was :

if (ledState == LOW &&((flowRate < 0.01)) (digitalWrite(GREEN,HIGH));
    {
    ledState = HIGH;
    }
    
    else digitalWrite (GREEN,LOW);

which did not work .. error in compiling /making order
Error message : expression cannot be used as a function, lighting up in red the '...If ..' string