How to interface two leds and two push button with 8051

8051c

i'm using 8051 mcu to do some tests.
i'm trying to use two input for two push buttons and two outputs for two Leds.
SW1 = push button 1
SW2 = push button 2
LED1 = led1
LED2 = led2

for example
-if i push S1 the Led1 will glow continuously.
-if i push S2 the Led2 will glow continuously.

These two command works independently.

So here what i tried:
only S1 and Led1 are working.
Please help, thank you.

#include <reg51.h>

sbit S1 = P2^0;
sbit S2 = P2^1;

sbit Led = P1^0;
sbit Led2 = P1^1;

void main()
 {
    S1 = 1;
    S2 = 1;

     while(1)  // For ever 
       {
         if(S1 == 0)  // if press Push button
          { 
            Led = 0;// ON LED ( active low )
            while(S1 == 0);// Wait here for release of push button
          }
      Led = 1;
       }

{
  if (S2 == 0)
    {
      Led2 = 0;
      while (S2 == 0);
       }
       Led2 = 1;
   }
}

Best Answer

You have un paired or extra curly brackets.

void main() {
    S1 = 1;
    S2 = 1;

    while(1) {  // For ever 
      if(S1 == 0) {  // if press Push button
         Led = 0;// ON LED ( active low )
         while(S1 == 0);// Wait here for release of push button
      }
      Led = 1;
      } // LOOPS BACK TO WHILE
    { // ***EXTRA***
    if (S2 == 0) {
      Led2 = 0;
      while (S2 == 0);
    }
    Led2 = 1;

   } // While?
} // Main?

Fixed:

void main() {
    S1 = 1;
    S2 = 1;

    while(1) {  // For ever 
      if(S1 == 0) {  // if press Push button
         Led = 0;// ON LED ( active low )
         while(S1 == 0);// Wait here for release of push button
      }

      Led = 1;

      if (S2 == 0) {
         Led2 = 0;
         while (S2 == 0);
      }

      Led2 = 1;

   } // While
} // Main

Related Solutions

Electronic – How to exit from the if statemet which is inside for loop and go back to the void loop in Arduino

Are you sure you need to exit at ANY time wherever the execution pointer is? Normally, you could just check the button press at the end of the while and for loops and call return when it is pressed.

Sometimes we think our program has to do something and break out of execution, but upon careful examination, we conclude that it can finish one loop interation and then quit.

Could you tell us what's done inside the loops, so we can make sure what's needed?

Edit: As I suspected, the problem with your program is that your delay intervals are too long, e.g. delay(1000) and delay(500), and you can't check for button presses while the program is waiting.

To fix that, create the following function, that will replace your calls to delay:

// waits for the specified miliseconds 
// or return (almost) immediately if button is pressed
// return value indicates whether button was pressed or not
boolean waitOrButtonPressed(int miliseconds) {
  for (int i = 0; i < miliseconds / 10; i++) {
    if (readButtons(5)) == 5)
      return true;
    delay(10);
  }
  return false;
}

Then, inside your for loop, replace your calls to delay(1000) by the following code:

if (waitOrButtonPressed(1000)) return;

The function I created will make your program wait almost like delay(), but will return true if a button was pressed during that time. If that happens, the if statement above will exit loop() which will be called again by the Arduino generated code.

Remember to keep the miliseconds to wait when you replace your calls to delay() to keep your program waiting behavior unchanged.

Edit 2: Ramblings

Cases like this remind me of the movie Tron, in which the main character is dragged into a computer, where time passes much slowlier than in real life. So, like in the movie, 1000 miliseconds (1s) is a LOT OF TIME for the MCU. You can do a whole lot more than waiting in that time. Try and break up the long Waits and do useful stuff with your MCU cycles.

Also, learn how to use interrupts, like others mentioned in their comments and answers. It's just another (a bit more complicated) way of doing stuff while you wait. In your case, interrupts could be use to detect the button press without the need to check it everytime everywhere. Here's a place to start learning about interrupts with Arduino.

Electronic – arduino – Controling 4 LEDs with 5 pushbuttons and Arduino

From your description, it seems you need to debounce the switch.

You can do this

in software or
in hardware

Since you seem to be using some kind of resistive ladder to read multiple buttons on one ADC port, this will be a little more complicated.

Best Answer

Related Solutions

Electronic – How to exit from the if statemet which is inside for loop and go back to the void loop in Arduino

Electronic – arduino – Controling 4 LEDs with 5 pushbuttons and Arduino

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