Using millis() to get elapsed time

Projects Programming
6

ofey:
Hi,

Yes I see it now. Seems to be working now. Do you think it is correct to update 'lastState' in the three places I did?

Not really. That's the current state if you do it at the start of the loop. More like (and note the use of "code" tags) ...

void loop()
  {
  byte currentState = digitalRead(photodiodePin);
  digitalWrite(ledTX, HIGH);   // turn the TX Infrared LED on
  Serial.println(currentState);    // Read the pin and display the value
  if(currentState == LOW && lastState == HIGH)
    {
    startTime = millis();
    }
  if(currentState == HIGH && lastState == LOW)
    {
    elapsedTime = millis() - startTime;
    Serial.print("Total time: ");
    Serial.println(elapsedTime);
    }
  lastState = currentState;
} // end of loop