PushButton as LED Switch (does not work)

Question

 #define LED 1//This pin goes to the LED  
 #define SWITCH 7//From Switch$  

void setup() {  
      pinMode(LED,OUTPUT);  
      pinMode(SWITCH,INPUT);  
}  
int state=0;//Initializing values of all three  
int val;  
int lastval=LOW;  

void loop(){  
      val=digitalRead(SWITCH);//Reads if switch is on or off  
      if(val==HIGH&&lastval==LOW){//Basically activates if the button was just pressed  
        state=1-state;//Changes state after button is pressed  
        digitalWrite(LED,state);//Enforces changed state to LED on or off  
        delay(50);//Just a simplistic debouncing  
      }
      lastval=val;//Store last value  
}  

Answer 1

Based on your response to my comment, it sounds like you have a floating input. When the button is NOT pressed, the pin isn't connected to ground or 5V so it is floating and picking up whatever stray electrical signals happen to be bouncing around the room.

The easiest way to handle buttons on an Arduino is to wire them between the pin and ground. Then in the code you use INPUT_PULLUP instead of INPUT for the pinMode call. Once you've done that then the pin will reliably read HIGH when the button is NOT pushed and will read LOW when the button IS pushed. Note that this is backwards of how newbies tend to think, but is really the more common way to handle a button.

Answer 2

I think the problem is in the lastval assignment and checking. During the bouncing, lastval will probably change several times. Within these changes the if statement is checked. If an even amount of changes are detected, the LED will change 4 times (being OFF again if it was OFF and On when On). Even if the user clicked possibly only one time. When an uneven amount of changes are detected it will be ok. So it's kind of luck when it works.

Use a proper debouncing technique (checking for some time if the switch is high or low and act on that directly).

Also do not use a boolean to flip that way, if you want it use a proper boolean:

boolean state;

...

state = !state;

However, I suggest using something like:

digitalWrite(LED, state ? HIGH : LOW); // HIGH if state is true, else LOW

And change the if condition in a proper debouncing check (plenty of examples, e.g. Arduino debouncing switch).