Arduino not recognizing when a timer reaches 0

Question

Alright, so I'm attempting to make a timer that will turn on a light after an hour. Currently I have it set to 5 seconds for testing. What is happening is whenever I start the program it won't recognize when the timer reaches 0. Here is my code

/*
Hour Alarm
An hour long alarm that allows breaks
Created by: Jaxon Reid
Last Edited: 19/5/2017

Pins:
Pin 13 = Led
Pin 2 = Button
*/
int secLeft=5;
const int led=13;
const int button=2;
const int buttonIn=4;
int buttonValue=0;
// Declares the button to reset as 2 and the lightbulb on pin 13
//the secLeft means the seconds until the light turns on and button value is for wether or not the button is pushed

void setup() {
  Serial.begin(2400);
  Serial.print("On  ");
  pinMode(13,OUTPUT);
  pinMode(button,OUTPUT);
  pinMode(buttonIn,INPUT);
}
// makes the led pin an input and opens the channel for the debugger
void loop() {
  int buttonValue=digitalRead(button);
  Serial.println("Checking time");
  if (secLeft<=0) {
    Serial.println("No time remaining");
    digitalWrite(13,HIGH);
    Serial.println("Light On");
    // If the time remaining is 0 then turn on the light
  }
  if (secLeft>0) {
    Serial.println("Time Remaining");
    digitalWrite(led,LOW);
    secLeft=(secLeft--);
    Serial.println(secLeft);
  }
  if (buttonValue==1) {
    int secLeft=5;
    Serial.println("Reset Timer");
    Serial.println(secLeft);
  }
  delay(1000);
}

Whenever I start it up it just starts reading

On 5
Checking time
Time remaining
5
Checking time
Time remaining
4
Checking time
Time remaining
3
Checking time
Time remaining
2
Checking time
Time remaining
1
Checking time
Time remaining
0
Checking time
Time remaining
-1
Checking time
Time remaining
-2

etc... So where did I go wrong is what I'm asking. Thanks!

The problem is int secLeft=(secLeft2--); where you are creating a second variable called secLeft within the scope of the if block. Ditch the int. This is the second question I have seen with this issue in the last 30 minutes. You probably also have the same issue with secLeft2 — Peter M
– Peter M, Commented Jun 17, 2017 at 22:10
Noter that you still have an int secLeft in the reset section — Peter M
– Peter M, Commented Jun 17, 2017 at 22:29

Peter M · Accepted Answer · 2017-06-17 22:22:51Z

2

As per comment and Majenko's answer you are current creating local variables called secLeft and secLeft2 inside the 'if block. These take precedence over the ones you have defined globally. Removing the in declarations from inside the if block will stop doing that and point you at the globally defined variables.

As to the rest of the code. If you have

secLeft=(secLeft2--);
secLeft2=(secLeft);

Then that translates to this sequence of instructions

Assign secLeft with the value of secLeft2
Decrement secLeft2
Assign secLeft2 with the value of secLeft

And in the end you do not change anything.

This is because you are using post-decrement on secLeft2 EG secLeft2--. This is a feature of C style languages.

I am not sure what you are even trying to do at this point.

answered Jun 17, 2017 at 22:22

Peter M

1485 bronze badges

Got it thankyou I was thinking it would decrement beforehand

Jayjaxx
– Jayjaxx

2017-06-17 22:27:16 +00:00
Commented Jun 17, 2017 at 22:27
To get pre-decrement you have to do --secLeft. C and C++ have both and they are both useful in their own way.

Peter M
– Peter M

2017-06-17 22:27:48 +00:00
Commented Jun 17, 2017 at 22:27

Add a comment |

Majenko · Accepted Answer · 2017-06-17 22:12:05Z

1

int secLeft=(secLeft2--); 
int secLeft2=(secLeft);

You are making 2 new variables there instead of using the existing ones.

answered Jun 17, 2017 at 22:12

Majenko

106k5 gold badges82 silver badges139 bronze badges

alright how do i fix that?

Jayjaxx
– Jayjaxx

2017-06-17 22:14:28 +00:00
Commented Jun 17, 2017 at 22:14
By not declaring new variables.

Majenko
– Majenko

2017-06-17 22:15:09 +00:00
Commented Jun 17, 2017 at 22:15
I have picked this up yesterday i learned C++ yesterday aswell what do i remove?

Jayjaxx
– Jayjaxx

2017-06-17 22:16:17 +00:00
Commented Jun 17, 2017 at 22:16
Remove the int from each line. Also, do you really want to reset secLeft2 to what it was before decrementing it? The second line looks a bit daft.

Majenko
– Majenko

2017-06-17 22:17:41 +00:00
Commented Jun 17, 2017 at 22:17
Now i just get 5,5,5,5,5 ...

Jayjaxx
– Jayjaxx

2017-06-17 22:19:32 +00:00
Commented Jun 17, 2017 at 22:19

| Show 4 more comments

James Waldby - jwpat7 · Accepted Answer · 2017-06-17 23:32:30Z

Besides problems mentioned in other answers, your use of button and buttonIn variables is messed up.

With button equal to 2, the pinMode(button,OUTPUT) statement initializes pin 2 to be an output. Pin 2 is low after reset and pinMode() doesn't change it.

When you say int buttonValue=digitalRead(button); the low value at pin 2 will be read into buttonValue. In the sketch, buttonValue will never be anything but low.

To fix this problem, get rid of buttonIn, and in setup() use pinMode(button,INPUT) to set button to be an input, not an output.

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