Code running in false if statement

Projects Programming
1

image

I am having this problem with the code in the screenshot where it will enter the if statement with the condition counter>temp, but even then what is printed to the serial is:
i

1

0

0

0

So it is acknowledging that counter and temp are equal while it's in the if statement that shouldn't be running if that is the case. I can even add Serial.println(counter>temp) and it will print 0 as well after it just, presumably, determined that was true. I assume I'm missing something obvious, but it's beyond me

2

Hello @asethbraun ,

Please post your entire code, not a picture of part of your code.

Please read How to get the best out of this forum if you need instructions.

There is insufficient information in what you have posted to provide a proper answer.

Thank you.

3 
int temp = 0;
int counter = 0; //This variable will increase or decrease depending on the rotation of encoder
int counter2 = 0;
    
void setup() {
  Serial.begin (9600);

  pinMode(2, INPUT); // internal pullup input pin (D2)
  
  pinMode(3, INPUT); // internal pullup input pin (D3)
//Setting up interrupt
  //A rising pulse from encodenren activated ai0()
  attachInterrupt(digitalPinToInterrupt(2), ai0, RISING);
   
  //B rising pulse from encodenren activated ai1()
  attachInterrupt(digitalPinToInterrupt(3), ai1, RISING);
  }
   
  void loop() {
  // Send the value of counter
    if(counter>temp){
      Serial.println ("i");
      Serial.println(counter == temp);
      Serial.println (counter);
      Serial.println(temp);
      Serial.println(counter>temp);
      temp = counter;
    }
  //delay(1000);
  }
   
  void ai0() {
  // ai0 is activated if DigitalPin D2 is going from LOW to HIGH
  // Check pin 2 to determine the direction
  //Serial.println(2);
  if(digitalRead(2)==LOW) {
  counter++;
  }else{
  counter--;
  }
  }
   
  void ai1() {
  // ai0 is activated if DigitalPin D3 is going from LOW to HIGH
  // Check with pin 3 to determine the direction
  if(digitalRead(3)==LOW) {
  counter--;
  }else{
  counter++;
  }
  }
4

I might be wrong, but these inputs declared this way do NOT have pullups, hence are noise-responsive.
Combine that with making them interrupts, and counter has a high probability of having a non-zero value by the time the if clause comes along. With nothing declared volatile, I think it's an unsolvable riddle, really, but others may differ.

5

All variables, that can be changed in irq routine, MUST BE declared with volatile keyword

volatile int counter = 0;
volatile int counter2 = 0;

otherwise you will observe weird behaviour of the program, similar to the one described above.

6

Yeah, I switched them with external pullups and didn't change the comments while debugging. Switching to volatile declarations doesn't remedy the situation alone, but changing the pins to internal pullups does seem to make it stop

7

That would imply your external resistors were wrong value, or wrongly wired.

1 Like
8

Obviously not when the if-condition is tested.

serial.println(counter == temp);

NOW they are equal.

I'm not sure that print statement is doing what you think it's doing... But maybe it's just me because I don't know what it's doing. :wink:

1 Like
9

nope, that's a relational test, not an assignment. Returns true, which prints as 1. No change to either variable.

1 Like
10

This doesn't explain why statements are executed when the condition evaluates to false.
Try to modify the code such way:

noInterrupts();
int counter_local = counter;
 interrupts();
  if(counter_local >temp){
      Serial.println ("i");
      Serial.println(counter_local == temp);
      Serial.println (counter_local);
      Serial.println(temp);
      Serial.println( counter_local>temp);
      temp = counter_local;
    }

to prevent the counter value from changing by interrupt while the main code is running

1 Like
11

@asethbraun ,

Thank you for posting all your code.

Not the answer to your question, but I thought you might find this interesting:

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