使用带按钮的 CCS 切换 LED

Question

I didn't understand what is wrong with my code. Here what I am trying to do is toggle a led when I press button. And I count my button hits with int count; . If the count number is even LED is high and else LED is low. But when I upload this program, LED stays on. And off only while I hold the button.

while(1){
int buttonState=input_state(pin_a0);

   if(buttonState != lastButtonState){
   count++;
   lastButtonState=buttonState;
     
      if(count%2==0){
      output_high(pin_b0);
      }
      else
      output_low(pin_b0);
}
delay_ms(50);
}

Answer 1

There is a problem in your logic. You have two changes while pressing the button. The first change is from 0 to 1 (pressing) and the second change is from 1 to 0 (releasing the button).

Try something like:

if(lastButtonState == 0 && buttonState == 1)

Answer 2

Is your button active-high or active-low ? Is your LED powered active-high or active-low? You need to give that information. I'll give an explanation assuming LED is powered when output is low. Then what follows is, assuming button is active-low, when your button is not pressed,

buttonState = 1;

So, since

lastButtonState = 0;

(at the start of the program, I'm assuming)

You will enter the if clause:

if(buttonState != lastButtonState){
...
}

This will increase your counter by one and make lastButtonState = buttonState;

Since count%2 will be 1 , your pin will be output_low(pin_b0); ... So, at the start of your program, your LED will be ON.

If you then press the button,

buttonState=0;

will happen and you will enter the if() clause, again. This will increase your counter by one. And then:

count%2 = 0;

Will happen. So, you will have

output_high(pin_b0);

As you can see, when you press the button, your LED will go off. And on when you release the button, your LED will go on Try this:

while(1){
   int buttonState=input_state(pin_a0);

   if(buttonState != lastButtonState){
   lastButtonState=buttonState;

      if(buttonState == 1){
          output_high(pin_b0); // LED is off
      }
      else
          output_low(pin_b0); // LED is on
   }
delay_ms(50);
}

You don't need the counter.

EDIT:

I see you have made this addition to your code:

if(buttonState==1) 
   count++;

This works. Yet is harder to understand. Try writing something easier to read.