Timers are widely used in industrial and domestic application for automating tasks. Microcontrollers can be used to design versatile and accurate timers with ease. Here I present a simple timer that can be used to turn on/off a load after user specified time.
The Timer uses a standard 16×2 lcd module for user interface (UI). User can set the time using a 3 button keypad.
After that Timer is started. While count down is in progress, the time left is displayed on screen.
The program use our LCD driver library more details of which can be found in here. Use avr-gcc + AVR Studio to compile.
The prototype was developed using xBoard MINI, a low cost easy to use ATmega8 development board. The program was burned to the MCU’s flash memory using eXtreme Burner – AVR Software and Hardware. A basic knowledge of working with different tools of AVR development is required, so please refer to following articles.
Note:
- Fuse Must be set as follows, HIGH FUSE=C9 LOW FUSE=FF (Very Important)
- If display is blank please adjust RV1
|
Part List
|
||
| 01 | ATmega8-16 PU | U1 |
| 02 | 16×2 LCD Module | LCD1 |
| 03 | 16 MHz Crystal | X1 |
| 04 | BC548 Transistor | Q1 |
| 05 | 1N4007 Diode | D1 |
| 06 | 4.7K Resistor | R1,R2 |
| 07 | 10K Variable Resistor | VR1 |
| 08 | 22pF Disk Capacitor | c1,c2 |
| 09 | 0.1uF Disk Capacitor | c3,c4 |
| 10 | Large Push Buttons | s1,s2,s3 |
| 11 | PCB Mountable Relay | RL1 |
Schematic (Circuit Diagram)
 |
Fig.: Relay Timer with AVR ATmega8 |
Program
/******************************************************
A Simple Device Timer project designed using ATmega8
AVR MVU. The Timer is usefully for keeping a device
"ON" for a specific period of time. After the set time
elapse the timer automatically turns the load off.
The Timer uses a standard 16x2 lcd module for user interface
UI. User can set the time using a 3 button keypad.
After that Timer is started. While count down is in
progress, the time left is displayed on screen.
The program use our LCD driver library more details
of which can be found in Web site.
Use avr-gcc + AVR Studio to compile.
Author: Avinash Gupta
E:Mail: [email protected]
Web: www.eXtremeElectronics.co.in
*** THIS PROJECT IS PROVIDED FOR EDUCATION/HOBBY USE ONLY ***
*** NO PROTION OF THIS WORK CAN BE USED IN COMMERIAL ***
*** APPLICATION WITHOUT WRITTEN PERMISSION FROM THE AUTHOR ***
EVERYONE IS FREE TO POST/PUBLISH THIS ARTICLE IN
PRINTED OR ELECTRONIC FORM IN FREE/PAID WEBSITES/MAGAZINES/BOOKS
IF PROPER CREDIT TO ORIGINAL AUTHOR IS MENTIONED WITH LINKS TO
ORIGINAL ARTICLE
Copyright (C) 2008-2009 eXtreme Electronics, India.
******************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>
#include "lcd.h"
//Connection of Load
#define LOAD_DDR DDRC
#define LOAD_PORT PORTC
#define LOAD_POS PC0
//Global variable for the clock system
volatile unsigned int clock_millisecond=0;
volatile char clock_second=0;
volatile char clock_minute=0;
volatile char clock_hour=0;
void Wait(uint8_t n)
{
uint8_t i,temp;
temp=n*28;
for(i=0;i<temp;i++)
_delay_loop_2(0);
}
void LoadOn()
{
LOAD_PORT|=(1<<LOAD_POS);
}
void LoadOff()
{
LOAD_PORT&=(~(1<<LOAD_POS));
}
main()
{
while(1)
{
LOAD_DDR|=(1<<LOAD_POS);
LoadOff();
//Enable Pullups on Keypad
PORTB|=((1<<PB2)|(1<<PB1)|(1<<PB0));
int8_t hr,min; //Target Time
hr=min=0;
//Initialize the LCD Subsystem
InitLCD(0);
//Clear the display
LCDClear();
//Set up the timer1 as described in the
//tutorial
TCCR1B=(1<<WGM12)|(1<<CS11)|(1<<CS10);
OCR1A=250;
//Enable the Output Compare A interrupt
TIMSK|=(1<<OCIE1A);
//Enable interrupts globally
sei();
LCDClear();
LCDWriteString(" Welcome ");
LCDWriteStringXY(0,1," Relay Timer ");
Wait(4);
LCDClear();
LCDWriteString("Set Time - 00:00");
LCDWriteStringXY(0,1," Start ^");
uint8_t selection=1;
uint8_t old_pinb=PINB;
while(1)
{
while((PINB & 0b00000111) == (old_pinb & 0b00000111));
//Input received
if(!(PINB & (1<<PINB2)) && (old_pinb & (1<<PB2)))
{
//Selection key Pressed
selection++;
if(selection==3)
selection =0;
}
if(!(PINB & (1<<PINB1)) && (old_pinb & (1<<PB1)))
{
//Up Key Pressed
if(selection == 1)
{
//Hour is selected so increment it
hr++;
if(hr == 100)
hr =0;
}
if(selection == 2)
{
//Min is selected so increment it
min++;
if(min == 60)
min =0;
}
if(selection == 0)
{
//Start Selected
break;
}
}
if(!(PINB & (1<<PINB0)) && (old_pinb & (1<<PB0)))
{
//Down Key Pressed
if(selection == 1)
{
//Hour is selected so decrement it
hr--;
if(hr == -1)
hr =99;
}
if(selection == 2)
{
//Min is selected so decrement it
min--;
if(min == -1)
min =59;
}
if(selection == 0)
{
//Start Selected
break;
}
}
old_pinb=PINB;
//Update Display
LCDClear();
LCDWriteString("Set Time - 00:00");
LCDWriteStringXY(0,1," Start ");
//Hour
LCDWriteIntXY(11,0,hr,2);
//Minute
LCDWriteIntXY(14,0,min,2);
if(selection == 0)
LCDWriteStringXY(0,1,">");
if(selection == 1)
LCDWriteStringXY(11,1,"^");
if(selection == 2)
LCDWriteStringXY(14,1,"^");
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
}
//Start the Load
LoadOn();
//Now start the timer
clock_hour = hr;
clock_minute = min;
clock_second =0;
LCDClear();
LCDWriteString(" Power Off In ");
while(1)
{
LCDWriteIntXY(4,1,clock_hour,2);
LCDWriteString(":");
LCDWriteIntXY(7,1,clock_minute,2);
LCDWriteString(":");
LCDWriteIntXY(10,1,clock_second,2);
if((clock_hour == 0) && (clock_minute == 0) && (clock_second == 0))
{
//Time Out
LoadOff();
LCDClear();
LCDWriteString("Load Turned Off");
while(1)
{
LCDWriteStringXY(0,1,"*Press Any Key*");
Wait(1);
LCDWriteStringXY(0,1," ");
Wait(1);
if((~PINB) & 0b00000111)
break;
}
break;
}
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
_delay_loop_2(0);
}
//Continue again
}
}
//The output compate interrupt handler
//We set up the timer in such a way that
//this ISR is called exactly at 1ms interval
ISR(TIMER1_COMPA_vect)
{
clock_millisecond++;
if(clock_millisecond==1000)
{
clock_second--;
clock_millisecond=0;
if(clock_second==-1)
{
clock_minute--;
clock_second=59;
if(clock_minute==-1)
{
clock_hour--;
clock_minute=59;
}
}
}
}
Downloads
- Complete Project in a ZIF file
- Compiled HEX file Ready to Burn in ATmega8 IC
My Prototype.
I used the xBoard MINI as a base board for making the timer. The external components attached were the LCD and 3 push buttons.
|
|
Fig.: AVR Timer Project Prototype. |
Using the Timer
The user interacts with the timer using 3 push buttons and the LCD module. The function of 3 keys are :-
- Select Key – Select Different items like hour,minute and start. It moves the arrow on screen to indicate which option is currently selected.
- Up/Increase Key – Increase the value. For example, select “minute” using “select” key and press this to increase its value.
- Down/Decrease Key – Same as above but it decreases the value.
When the timer is powered up the load is in off state. A welcome message is shown. Then you can set the time using the above buttons. After that move to “start” option by using select key. Then press any key to start the timer. Now the screen shows the count down and the load is powered on. When count down reaches 0 the load is turned off. The pictures and videos below illustrate the process.
 |
Fig.: Use SELECT key to move between options. |
 |
Fig.: Count down in progress (HH:MM:SS). |
 |
Fig.: The Load Turned Off.
Sumber: https://extremeelectronics.co.in/avr-projects/avr-project-relay-timer-with-atmega8-avr-mcu/ |