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Troubleshooting why Arduino logical operators doesn't compute

colporteur

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How would you write the expression to test sensors Departure (A or B) HIGH AND Arrival (A or B) HIGH?

The first else if statement shown below doesn't work. Departure A OR Departure B HIgh AND Arrival A OR Arrival B High. The OR doesn't work. Only when both Departure A AND B are HIGH the serial print. The same applies to the third else if statement both Departure A and B have to be low for the statement to function. What am I coding wrong for the OR?

      if ((digitalRead(s1DeparturePinA) == LOW || digitalRead(s1DeparturePinB) == LOW) &&
          (digitalRead(s1ArrivalPinA) == HIGH || digitalRead(s1ArrivalPinB) == HIGH))
        {
         Serial.println(F("Train on siding 1 status DEPARTURE")); 
         delay(1);
        }
      else if ((digitalRead(s1DeparturePinA) == HIGH || digitalRead(s1DeparturePinB) == HIGH)&&
               (digitalRead(s1ArrivalPinA) == HIGH || digitalRead(s1ArrivalPinB) == HIGH))
        {
          Serial.println(F("Train on siding 1 status IN TRANSIT"));
          delay(1);
        }
      else if ((digitalRead(s1DeparturePinA) == HIGH || digitalRead(s1DeparturePinB) == HIGH) &&
               (digitalRead(s1ArrivalPinA) == LOW || digitalRead(s1ArrivalPinB) == LOW))
        {
          Serial.println(F("Train on siding 1 status ARRIVAL"));
          delay(1);
          s1ArrivalDetect = LOW;
        }
      else if ((digitalRead(s1DeparturePinA) == LOW || digitalRead(s1DeparturePinB) == LOW) && 
               (digitalRead(s1ArrivalPinA) == LOW || digitalRead(s1ArrivalPinB) == LOW) &&
                s1ArrivalDetect == LOW)
        {
          Serial.println(F("Train on siding 1 status STOP"));
          delay(1);       
        trainOneOut = LOW; //train selection flip_flop L=train on siding 2
        s1ArrivalDetect = HIGH;
        digitalWrite(l1_TurnoutL, LOW);  //unset departure and arrival turnouts for train1
        digitalWrite(s1_Power, LOW);        //unset power on for train1
        digitalWrite(l1_TurnoutR, HIGH);  //set departure and arrival turnouts for train2
        digitalWrite(s2_Power, HIGH);        //set power on for train2
        }
  • in reply to colporteur

    NOPE! GOTA Have Debounce.  so you have 4 switches, that are open or closed. that's eight states. so let's cut it in half as we only care about the Active States. first I would take a 4 input or-gate and tie it to each switch and to 4 Arduino inputs. take the output of the or-gate go through the Schmitt trigger to an ISR. Now when the ISR is triggered you read the 4 inputs to find the active one.

    KISS Principle (Keep It Simple Stupid) This applies to everybody. 

    OPS! you need two ISRs one for each track. and I would not use the quad input or gate. use 2 2-input or gates. 

  • in reply to colporteur

    If you have an oscilloscope you can watch the switch and see if it is bouncing. I would guess that it does. What the software I linked does is check to make sure it doesn’t change state (or bounce as they say) faster than a human can push and let go of a button. Your switch may be chattering for quite some time. If you don’t have an oscilloscope maybe set the Arduino to print in a simple loop for one section of track as fast as it can and look for a period where it changes output from 0 to 1 several times in a row when the train moves. If so, how long does it last?

  • Most switch bounce issues can be handled with software as mentioned by others in this thread, although I prefer to design 100% instant debouncing in hardware, because it operates faster and with no ambiguity. Of course to design it requires knowledge about the hardware in question. And keeping my hard hat on, even your control logic is pretty trivial in hardware. You might find that mechanical inertia eliminates any bounce issues in a hardware solution.

  • in reply to colporteur

    My proposal was not to focus on the state of the sensors but on the change of state, that from my point of view simplifies the logic.

    An Arrival is a change of state of the Arrival sensor signal from low to high (RISING).

    And one Departure is a state change of the departure sensor signal from high to low (FALLING).

    Everything that happens in between I don't care.

    Not all pins can trigger interrupts. In your case, I think you are using an Arduino MEGA board, it has 6 pins (2, 3, 18, 19, 20, 21) with the possibility of enabling interrupts in case I2C is not used with pins 20 and 21. In that case you would have 4 pins only enabled for interruptions.

    https://www.arduino.cc/reference/en/language/functions/external-interrupts/attachinterrupt/

  • in reply to fmilburn

    This Arduino debounce library works pretty well: www.arduino.cc/.../

  • Thanks for all the input. I examined the suggestions and then tried to envision a solution. I don't have the programming experience that would give me lots of options to draw solutions from. In the end, I worked my way out by shear testing.

    I followed the suggestion to read the sensor, assigning it to a variable and then evaluating the variable. Oh yeah, I displayed the variables also, that helped. Then I set about using the logical operators to achieve my end goal. I tried to incorporate the ISR concept but couldn't see a way to make it fit. Again that experience thing.

    The code definitely is not as concise as a seasoned programmer would have created but so far it appears to work.