Troubleshooting why Arduino logical operators doesn't compute

First assign each pin's status to a variable' then print that variable to the serial monitor.

You can then see if it's related to your logic, or to a pin not being correctly read.

Added bonus: if you then use those variables in your comparisons, yoy have less gpio function calls.

Added bonus 2: consistent state throughout the evaluation. In your code, there is no guarantee that these pins have the same status during the logic's execution.

Bare with me while I carve out an understanding.

Before the first if statement, read the pins and assign the status to a variable. Then all the conditional statements are evaluated against those recorded states. The states are read each time through the loop.

Yes. And if you want to test the logic, I'd first manually assign TRUE or FALSE to the variables, instead of reading pins. And see if the code does what you expect.

If it does, then assign the variables from pin state, and try again.

... also, if your input changes are caused by a mechanical event (switch, optocoupler detecting movement, magnetic sensor) , you may need to debounce/clean the input signals.

I would use some kind of linear encoder. If in your case you only have to detect the arrival and departure always in the same direction, the logic is reduced to detecting the rising edge of one sensor and the falling edge of the other.

You can use interrupt service routines to detect both the rising edge transition and the falling edge transition.

dougw has a good project on the subject.

The Logical Project

Intro I always had a lot of fun designing digital circuits that used Boolean logic, but these days it is rare to see designs with lots of discrete gates. With this little project I'm going to have some…

By dougw over 4 years ago in Digital Fever > Blog

14 comments

I based on the same for this project that you see in the video. In this case I needed to detect the direction of movement, it's a different case but it uses the same quadrature encoder principle using a DIY magnetic linear encoder with two magnetic reed switches and a magnet.

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RE: Troubleshooting why Arduino logical operators doesn't compute RE: Feedback on 555 timer Schmidt Trigger design VenTTracker #13 - Project wrap-up and Lessons learned VenTTracker #06 -  Window Sensor Prototype

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In this blog you can get the complete source code for this solution.

VenTTracker #06 -  Window Sensor Prototype

One of the main components of our ventilation routine monitoring project is the sensor for the status of doors, windows and blinds. During this week we have given a boost to the creation of that sensor…

By javagoza over 4 years ago in Design For A Cause 2021 > Blog

2 comments

I like the debounce idea for use on reading the sensors. I reviewed your application and got lost. Not a programmer. I then went in search of simplified code examples. I'm thinking of trying to assemble code for a test first to see if I can get a working model. I need some of that anti-aging formula to grasp this stuff:)

For example 

In setup set the two ISRs

// detect rising edge for switch A
attachInterrupt(digitalPinToInterrupt(s1ArrivalPinA), isrArrivalSwitchRising, RISING);

// detect falling edge for departure
attachInterrupt(digitalPinToInterrupt(s1DeparturePinB), isrDepartureSwitchFalling, FALLING);

Then define the two ISR, two functions

void isrArrivalSwitchRising() {
   state = TRAIN_ARRIVED 
}

void isrDepartureSwitchFalling() {
   state = TRAIN_DEPARTED 
}

and in your loop method check for state changes

if (state==TRAIN_ARRIVED) {
   state == TRAIN_PARKED;
   doMyArrivingStuff();
}

if(state==TRAIN_DEPARTED) {
   state == TRAIN_RUNNING;
   doMyDepartureStuff();
}

If you remove the else clause and run your code as 4 separate if statements you will see their are input cases that overlap. The only way for the first if statement to fail is for both departure inputs to be high.

Did you hear that? That was my head hitting the desk:) I'm envious of the knowledge, yet my age creates limits on what I can use or retain.

attachInterrupt(digitalPinToInterrupt(s1ArrivalPinA), isrArrivalSwitchRising, RISING);

This call, if the sensor input s1ArrivalPinA is RISING (i.e. HIGH) run the isr routine? I will get this a little bits at a time.

HUmmm...I don't see that. Will look again.