Problems with ButtonStateChange Tutorial Sketch

Forum 2005-2010 (read only) Software Syntax & Programs
1

I'm working through the tutorial sketches at http://arduino.cc/en/Tutorial/HomePage and am stymied by the output in the serial monitor window, which looks like this:

on
number of button pushes: 1
off
on
number of button pushes: 2
off
on
number of button pushes: 3
off
on
number of button pushes: 4
off
on
number of button pushes: 5
off

This does not reflect the output of the Arduino itself, which begins with the LED on, turns it off after the first button push, and then turns it on whenever the total number of button pushes is a multiple of four.

I think the serial monitor output should look like this:
on
number of button pushes: 1
off
number of button pushes: 2
off
number of button pushes: 3
off
number of button pushes: 4
on
number of button pushes: 5
off

I transcribed the code by hand so I could trace out what each line did. When it didn't work correctly, I copied the code straight from the tutorial and got the same result. Here's the code:

const int  buttonPin = 2;    // the pin that the pushbutton is attached to
const int ledPin = 13;       // the pin that the LED is attached to

int buttonPushCounter = 0;   // counter for the number of button presses
int buttonState = 0;         // current state of the button
int lastButtonState = 0;     // previous state of the button

void setup() {
   pinMode(buttonPin, INPUT);
   pinMode(ledPin, OUTPUT);
   Serial.begin(9600);
}

void loop() {
   buttonState = digitalRead(buttonPin);

 if (buttonState != lastButtonState) {
     if (buttonState == HIGH) {
       buttonPushCounter++;
      Serial.println("on");
      Serial.print("number of button pushes:  ");
      Serial.println(buttonPushCounter, DEC);
    } 
    else {
       Serial.println("off"); 
    }

     lastButtonState = buttonState;
  }
  
 if (buttonPushCounter % 4 == 0) {
    digitalWrite(ledPin, HIGH);
  } else {
   digitalWrite(ledPin, LOW);
  }
  
}

off

Any suggestions? I feel like I might have a set of curly braces that are not paired correctly in the "if else" section, but I'm not sure.
Also, because there is not an "else" to go with every "if", I am wondering if the "else" is paired with the wrong "if", but my eyes are getting bleary from studying it.

2

A button press and a button release are not the same thing. The output you showed that you think you should be getting treats presses and releases as equal. The output that you are getting shows, clearly, that they are not.

The code you posted shows the output I would have expected it to produce, and that you showed that it did produce.

Perhaps the fact that you are storing the current button state only when the current button state is not equal to the previous button state is a source of the confusion/misunderstanding.

3

Ah Hah! Paul, you are exactly right. I just wasn't seeing it.

I can now see exactly why it is doing what it does. I thought the code was reading the button state as a proxy for the LED pin state. I see now that it is telling me whether or not the button is on or off, which is a much more useful thing to know.

Now I am going to alter the code so that the serial monitor tells me both whether the LED is on and whether the button is depressed.

Thank you for your help.

4