Time Switch_4: Designing the alarm.

In the last post we have been able to develop the design so that it can now measure seconds. Now it’s just a matter of few lines of coding before we convert it to a alarm.

Basically, we can now measure minutes. If we keep a value in a register, let’s say 10, and keep on decreasing the register by one for each minute then we will come to the value zero in 10 minutes. If we reach zero we can program the processor such that it will print “Alarm” in the LCD so that we can see that our program works.

Almost all the coding will be done inside the interrupt routine,
Following is how the interrupt routine is going to be.

void interrupt(){

INTCON.GIE = 0;            // global interrupts disabled

if(INTCON.T0IF){             // handling the timer0 interrupt

timer_val++;

if(timer_val == 15000){          // 19531.25 overflows per second

timer_sec++;

timer_val = 0;

 if(timer_sec = 60){

  //minute

time_val--;

 i(time_val == 0){

Lcd_Cmd(_LCD_CLEAR);

Lcd_Cmd(_LCD_CURSOR_OFF);

Lcd_Out(1,1,”Alarm”);

 }

 }

 timer_sec = 0;

}

}

}

INTCON.T0IF = 0;           // clearing the interrupt flag bit

INTCON.GIE = 1;             // enabling global interrupts

}

 This is what is happening in the above code,

1.       Calculate a second by using timer_val variable.

2.       Calculate number of seconds elapsed using timer_sec variable.

3.       if(timer_sec = 60) will only be true if number of seconds become 60 and that is a minute.

4.       If it’s a minute our known value time_val will be reduced by one.

5.       When time_val is equal to zero LCD will show “Alarm”.

Now we have the alarm. Basically this is what we needed. Now if we tell our processor to drive a relay once the alarm is being triggered it will be enough to switch on a light. J

In the next post I will talk about developing the program to drive a single relay which is even easier than this.

Thank you.