! Operator and HIGH LOW

Using Arduino Programming Questions
#1

Hi there,

just courious where was my mistake - i want to read a button, connected to a pin and GND with

pinMode(pin, INPUT_PULLUP);

if (!digitalRead(pin)) { … } // This did not work while

if (digitalRead(pin)==LOW) { … } // This works?

#2

I don't see a reason why the first shouldn't work but it's very easy to understand the intent of the second code and it doesn't make any assumptions about the value of LOW so I think it's better anyway.

#3 
void setup()
{
  Serial.begin(115200);
  pinMode(A1, INPUT_PULLUP);
}

void loop()
{
  if (digitalRead(A1))
  {
    Serial.println("true");
  }
  if (!digitalRead(A1))
  {
    Serial.println("false");
  }
  delay(1000);
}

Works fine for me.
Button not pressed prints true
Button pressed prints false

Please post a complete program showing that it does not work for you

#4

Ah sorry, i just see i did not tell you the complete truth.

The complete line was

if (!digitalRead(pin) || intCnt > 36/8) { // blink LED .. }

vs. the functioning

if (digitalRead(pin)==LOW || intCnt > 36/8) { // blink LED .. }

intCnt is increased in a watchdog timer ISR - and i see the right action after 5 watchdog wakeups, so the right part of the expression works. I guess it has something to do with operation order and brackets.

#5

Please have a look at How to use the forum. Especially the part about code snippets and code tags :wink:

Is intCnt declared volatile?

#6

yes, is volatile. Sorry i was to blind to see very first formatting option shame on me i 've just seen link, image etc.

#7 
intCnt > 36/8

Is intCnt an int by any chance ?

#8

UKHeliBob:

intCnt > 36/8

Is intCnt an int by any chance ?

Yes it is - is it a (the) problem?

#9

It's not a problem if you understand that 36/8 equals 4 not 4.5 and you are all right with that.

#10

UKHeliBob:
It's not a problem if you understand that 36/8 equals 4 not 4.5 and you are all right with that.

That's interesting :slight_smile: yes i am aware of. originally there was 3600, because i want a timeout of 1 hour with an 8sek. watchdog timer and was too lazy to calculate myself. killing 2 "0"s to debug was again the laziest approach :slight_smile:

#11

See what

if ( ( !digitalRead(pin) ) || ( intCnt > 36/8 ) ) { // blink LED .. }

does.

Sometimes you have to force the compiler to do what makes sense to you. Clarity is your friend.

If your code is not delay-bound you might find it reading button bounces. If you don’t know about those, you may end up trying to debug the wrong problem.

#12