8-bit MicrocontrollersのトピックRe: to read a switch

to read a switch

avditkohli — Wed, 23 Jul 2014 07:20:49 GMT

Hi,

I am trying to read a mechanical switch to initialise a LCD every time the switch is turned ON. I use the following code :

if(ON==0)		// is the switch OFF
	{
		delay_ms(8);
		if(ON==1)		// If turned ON
			lcd_init();
	}

The LCD does not initialise correctly when I turn ON the switch.

Regards,

Avdit

Re: to read a switch

arpitaagarwal-b — Wed, 23 Jul 2014 08:48:20 GMT

Hello Avdit,

With the given details, problem is not clear.

It seems you might be having this code in while loop and using GPIO data register directly to check high and low.

When you will turn ON the mechanical switch, there will be glitches at the I/O port. Because of which you can see flickering in LCD but this should settle down.

I would suggest to use KBI edge detect interrupt to detect switch ON/OFF position. This will avoid any glitches.

-Arpita

Re: to read a switch

wendersonolivei — Thu, 24 Jul 2014 01:58:19 GMT

Hi Avdit,

I think which you problem is in a multiple inicializations, or glitches at I/O.

If you can use a simple debounce filter to avoid glitches at I/O, like the example code:

#define TRESHOLD    20 //Here you will define a treshold for the debounce filter
byte debounce = 0;
bool state = 0; //State of your input
void Main()
{
     [...]
     for(;;)
     {
         if(input && (debounce < TRESHOLD)) debounce++;
         else
         {
               if(!input && debounce) debounce--;
         }
         if(debounce >= TRESHOLD) state = 1;
         else state = 0;

          if(state)
          {            
               lcd_init(); //Initializes your lcd
               break; //Get out from loop, to not initialize again
          }
     }
     [...]
}

I hope it helps!

Re: to read a switch

avditkohli — Thu, 24 Jul 2014 06:51:36 GMT

Hi Wenderson,

Thanks for your reply. I managed to solve it using a delay of around

50ms to read the change in state of the input.

Avdit

On Thu, Jul 24, 2014 at 7:29 AM, Wenderson Oliveira <

Re: to read a switch

avditkohli — Thu, 24 Jul 2014 14:22:48 GMT

https://community.freescale.com/message/419243#419243