Interrupt help (solved)

Other Hardware Sensors
1

Hi all,

I'm sure I'm making a simple newbie mistake here. What I need to happen is do some work when an interrupt (INT 0) is detected; like light an LED and also print some text on an LCD. When I run the sketch below, the LED stays constantly lit and the LCD prints the text regardless of any interrupt being detected (I have a sensor attached to it--which I know works fine).

Any tips/advice you can give would be greatly appreciated!

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x20,20,4);

volatile boolean flag;
const int led = 5;

// Interrupt Service Routine (ISR)
void isr ()
{
 flag = true;
}  // end of isr

void setup ()
{
  attachInterrupt (0, isr, RISING);  // attach interrupt handler
  pinMode (led, OUTPUT);
  
  lcd.init();   // initialize the lcd 
  lcd.backlight();
  
}  // end of setup

void loop ()
{
  if (flag)
    {
    // interrupt has occurred
    digitalWrite(led,HIGH);
    lcd.clear();
    lcd.print("Detected");
    
    }
  
}  // end of loop
2

Assign an initial value to flag.
Clear flag once you have acted upon it.

3

When I run the sketch below, the LED stays constantly lit

because there's no code to turn it off?

4

Grumpy_Mike:
Assign an initial value to flag.
Clear flag once you have acted upon it.

Can you give me an example? (sorry, I'm still learning).

5

Seriously?
1)

volatile boolean flag = false;

flag = false;
6

Grumpy_Mike:
Seriously?
1)

volatile boolean flag = false;

flag = false;

That did the trick! Sorry for the newbie question. Thanks so much for your help!

7

Hi Velocity101

I'm a newbie to Arduino myself and am yet to get my hands on any hardware :frowning: though I have got some programming background from many years ago.

I know you have solved the issue by initialising the flag as suggested, though I thought I'd chip in and add to what has already been said.

I'm not sure how much programming experience you have but one thing I learn early was "uninitialized variables are bad news". The reason is they can cause unpredictable behaviour.

This is especially true when you consider in C (unlike most other programming languages) there is no true boolean variables - they are stored as unsigned integers.

a value of 0 is interpreted as False
any other (non-zero) value is interpreted as true.

This means that is you define a boolean variable it's more than likely to be "true" - unless you initialise it to 0 (false).

If you already know this then feel free to ignore me an hopefully it helps someone else...

8

TallOne:
Hi Velocity101

I'm a newbie to Arduino myself and am yet to get my hands on any hardware :frowning: though I have got some programming background from many years ago.

I know you have solved the issue by initialising the flag as suggested, though I thought I'd chip in and add to what has already been said.

I'm not sure how much programming experience you have but one thing I learn early was "uninitialized variables are bad news". The reason is they can cause unpredictable behaviour.

This is especially true when you consider in C (unlike most other programming languages) there is no true boolean variables - they are stored as unsigned integers.

a value of 0 is interpreted as False
any other (non-zero) value is interpreted as true.

This means that is you define a boolean variable it's more than likely to be "true" - unless you initialise it to 0 (false).

If you already know this then feel free to ignore me an hopefully it helps someone else...

Hi TallOne,

I definitely appreciate your tip. Thanks!