Go4Expert - how to detect the push button

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how to detect the push button

Hi..
I'm new in programming microcontroller in c. And I was given an assignment to write a simple program to turn 'ON' and "OFF' the LED by pressing push buttons. The microcontroller i'm using is PIC18F4620. And i'll need 1 LED and 2 push buttons to program this. I have already tried to write the program but it doesnt work. Here is my program:

Code:

#include <p18f4620.h>

 

#pragma config OSC = HS

#pragma config WDT = OFF

#pragma config LVP = OFF

 

#define btn_on                 PORTBbits.RB4

#define btn_off                 PORTBbits.RB5

#define led                       PORTAbits.RA0

 

void press(void);

void on(void);

void off(void);

 

void main(void)

{

             TRISA = 0;                                   //set Port A(LED) as output

             PORTAbits.RA0 = 0;                     //reset LED

    

             while(btn_on != btn_off)         //wait for btn press

    

             if (btn_on = 1)                          //btn on pressed

             on();

 

             if (btn_off = 1)    //btn off pressed

             off();

}

 

    void on(void)

    {

              while(btn_on);                      //wait for btn(RB4) released

              PORTAbits.RA0 = 0x0F;                  //on LED

    }

    

    void off(void)

    {

             while(btn_off);                  //wait for btn(RB5) released

              PORTAbits.RA0 = 0x00;              //off LED

    }

the underline statement is the one i not sure whether is correct or not. I have being working on this for a week. But still cant get the program run correctly. Hope to get some guide. Thank.

Re: how to detect the push button

Don't compare btn_on to btn-off, they're not the same. Read the state of the button and save it. Then read the state of the button and compare it to the saved state to detect a change. On a change, perform your action and save the new state.

Re: how to detect the push button

how do i read the state of the button and save it..??

Re: how to detect the push button

You're the one with the specification, so I just have to guess. It looks like (from your code) the switch is a single pole, double throw with the poles wired between pins 4 and 5 of port B and common tied to either ground or V++. Actually, I'd build it so that it was a SPST just wired between the two pins.

Presume that pin 4 is ground when the switch is pressed and V++ when it isn't. A normal switch is going to bounce for a while when it makes contact. I'd check pin 4 to see if it was ground. If it was, I'd check again something like 20 ms later. If it was still ground I'd set a variable to say that it was pressed, and turn on the LED. I would then check it repeatedly to see when it went to V++ (switches don't usually bounce on the break, only on the make). When it did, I'd set the LED off.

If your system does more than monitor the switch, then you'll want a non-blocking operation. This means making the check when you receive an appropriate timer interrupt or a hardware interrupt tied to the switch pin.

Again, this is just generic. You're the one with the parts and their specs.