Time Switch_5: Driving a relay.

In the previous post I mentioned about the designing the alarm. Now it’s the time to drive just one light. Within the microcontroller we don’t need to do much, just one or two entries. But in hardware we have some new things coming in to our design to facilitate the tripping of the light.

Following image will let you know how to connect the relay to the circuit.

We should connect the microcontroller to the Base of the transistor and then the transistor to the relay. That is because the current from the microcontroller is not enough to drive the relay and we need to amplify it using the transistor. The D1 diode is used to provide a current path in the transient stage of the solenoid inside the relay.

Following is the relay connected to the microcontroller.

Finally we should alter the program inside the microcontroller. Following is the alteration we need. There what we do is instead of driving the LCD we program microcontroller so that it will drive the relay by making a pin in microcontroller HIGH.

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){

PORTA.RA0 = 1;

 }

 }

 timer_sec = 0;

}

}

}

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

INTCON.GIE = 1;             // enabling global interrupts

}

That's basically it.

Thank you.

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.