Using Millis with optical encoder

Projects Programming
12

If I place this

noInterrupts() ;
if( counter != temp ){
  Serial.println (counter);
  temp = counter;
  }
interrupts() ;

into the code it still behaves as before wildbill.
Like this...

/*
  In this example, we're using optical encoder LPD3806-400BM.
  Only OUT-B (white wire) is used and connected to pin 2 on Arduino.
  This allows a count of up to 400 pulses only.
  Connecting both outputs will give a count of up to 800 pulses!
*/
const int ledPin =  LED_BUILTIN;
unsigned long startTime;
int lastCounterReading = 0;
int ledState;
unsigned long interval = 50;
int lastTempReading = 0;

volatile long temp, counter = 0; //This variable will increase or decrease depending on the rotation of encoder

void setup() {
  Serial.begin (250000);
  pinMode(2, INPUT_PULLUP); // internal pullup input pin 2
  pinMode(ledPin, OUTPUT);

  //Setting up interrupt
  //A rising pulse from encodenren activated ai0(). AttachInterrupt 0 is DigitalPin nr 2 on moust Arduino.
  attachInterrupt(0, ai0, RISING);
}

void loop() {
  // Send the value of counter
  noInterrupts() ;
  if ( counter != temp ) {
    Serial.println (counter);
    temp = counter;
  }
  interrupts();
  if (counter == 100)
  {
    if (lastCounterReading != 100)
    {
      ledState = 1;
      startTime = millis();
    }
  }
  lastCounterReading = counter;
  if (ledState)
  {
    if (millis() - startTime <= interval)
    {
      digitalWrite(ledPin, HIGH);
    }
    else
    {
      digitalWrite(ledPin, LOW);
      ledState = 0;
    }
  }
}

void ai0() {
  // ai0 is activated if DigitalPin nr 2 is going from LOW to HIGH
  if (digitalRead(2) == LOW) {
    counter--;
    if (counter == 0)
      counter = 400;
  }
  else {
    if (counter == 400)
      counter = 0;
    counter++;
  }
}

However, if I do this...

/*
 In this example, we're using optical encoder LPD3806-400BM.
 Only OUT-B (white wire) is used and connected to pin 2 on Arduino.
 This allows a count of up to 400 pulses only.
 Connecting both outputs will give a count of up to 800 pulses! 
 */
const int ledPin =  LED_BUILTIN;
unsigned long startTime;
int lastCounterReading = 0;
int ledState;
unsigned long interval = 50;
int lastTempReading = 0;

volatile long temp, counter = 0; //This variable will increase or decrease depending on the rotation of encoder
    
void setup() {
  Serial.begin (250000);
  pinMode(2, INPUT_PULLUP); // internal pullup input pin 2 
  pinMode(ledPin, OUTPUT);
  
   //Setting up interrupt
  //A rising pulse from encodenren activated ai0(). AttachInterrupt 0 is DigitalPin nr 2 on moust Arduino.
  attachInterrupt(0, ai0, RISING);
  }
   
  void loop() {
  // Send the value of counter
  if( counter != temp ){
  Serial.println (counter);
  temp = counter;
  } 
   if (temp == 100)   
  {
    if (lastTempReading != 100)   
    {
      ledState = 1;
      startTime = millis();
    }
  }
  lastCounterReading = counter;
   if (ledState)
  {
    if (millis() - startTime <= interval)
    {
      digitalWrite(ledPin, HIGH);
    }
    else
    {
      digitalWrite(ledPin, LOW);
      ledState = 0;
    }
  }  
}
  
  void ai0() {
  // ai0 is activated if DigitalPin nr 2 is going from LOW to HIGH
  if(digitalRead(2)==LOW) {
  counter--;
   if (counter == 0)      
        counter = 400;
    }
    else {
      if (counter == 400)
        counter = 0;  
      counter++;
  }
  }

It works. What am I missing?