Multiplexed Seven Segment Displays – Part II0digg

Hi Friends, In last tutorial we discussed about Multiplexing Seven Segment Displays. So

you must be very much familier with the therory. Now let us write the code and design a

small project that will make you expert in using these displays in your own projects. We

will make a system that can display any number between 0-999 using three of these

displays. We will write a function Print() that we can use on own later projects to easily

write integers onto displays. Once we have successfully tested this function we can add

to to any project without any problem. This concept of code reuse will make bigger

project both easy to make and far less painfull. In this sample project we will test our

function by using it in a loop to print all numbers from 0-999.

for(i=0;i<1000;i++)

{

Print(i);

Wait();

}

We will assemble the project in a breadboard as shown below.

Fig - Multiplexed Seven Segment Displays.

The Circuit Diagram.

You can use a Home Made AVR Devboard or a low cost xBoard MINI to experiment with

seven segment displays. In the picture I have used xBoard MINI. The project is designed

with ATmega8 but can easily be done through ATmega16 or ATmega32. The crystal

value is not so critical for this you can use 12 MHz or 16 MHz it would only change the

refresh rate of displays.

Fig - Multiplexed Seven Segment Displays.

The Code

/*

Description: Program to demonstrate the use of Seven

Segment Displays In Multiplexed Mode.

________________________________________________________

Author: Avinash Gupta

Date: 11 Oct 08

Web www.eXtremeElectronics.co.in

*/

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay_basic.h>

#define SEVEN_SEGMENT_PORT PORTD

#define SEVEN_SEGMENT_DDR DDRD

volatile uint8_t digits[3];

void SevenSegment(uint8_t n,uint8_t dp)

{

/*

This function writes a digits given by n to the display

the decimal point is displayed if dp=1

Note:

n must be less than 9

*/

if(n<10)

{

switch (n)

{

case 0:

SEVEN_SEGMENT_PORT=0b00000011;

break;

case 1:

SEVEN_SEGMENT_PORT=0b10011111;

break;

case 2:

SEVEN_SEGMENT_PORT=0b00100101;

break;

case 3:

SEVEN_SEGMENT_PORT=0b00001101;

break;

case 4:

SEVEN_SEGMENT_PORT=0b10011001;

break;

case 5:

SEVEN_SEGMENT_PORT=0b01001001;

break;

case 6:

SEVEN_SEGMENT_PORT=0b01000001;

break;

case 7:

SEVEN_SEGMENT_PORT=0b00011111;

break;

case 8:

SEVEN_SEGMENT_PORT=0b00000001;

break;

case 9:

SEVEN_SEGMENT_PORT=0b00001001;

break;

}

if(dp)

{

//if decimal point should be displayed

//make 0th bit Low

SEVEN_SEGMENT_PORT&=0b11111110;

}

}

else

{

//This symbol on display tells that n was greater than 9

//so display can't handle it

SEVEN_SEGMENT_PORT=0b11111101;

}

}

void Wait()

{

uint8_t i;

for(i=0;i<10;i++)

{

_delay_loop_2(0);

}

}

void Print(uint16_t num)

{

/*

This function breaks apart a given integer into separete digits

and writes them to the display array i.e. digits[]

*/

uint8_t i=0;

uint8_t j;

if(num>999) return;

while(num)

{

digits[i]=num%10;

i++;

num=num/10;

}

for(j=i;j<3;j++) digits[j]=0;

}

void main()

{

uint16_t i;

// Prescaler = FCPU/1024

TCCR0|=(1<<CS02);

//Enable Overflow Interrupt Enable

TIMSK|=(1<<TOIE0);

//Initialize Counter

TCNT0=0;

//Port B[2,1,0] as out put

DDRB|=0b00000111;

PORTB=0b00000110;

//Port D

SEVEN_SEGMENT_DDR=0XFF;

//Turn off all segments

SEVEN_SEGMENT_PORT=0XFF;

//Enable Global Interrupts

sei();

//Infinite loop

//Print a number from 1 to 999

while(1)

{

for(i=0;i<1000;i++)

{

Print(i);

Wait();

}

}

}

ISR(TIMER0_OVF_vect)

{

/*

This interrup service routine (ISR)

Updates the displays

*/

static uint8_t i=0;

if(i==2)

{

//If on last display then come

//back to first.

i=0;

}

else

{

//Goto Next display

i++;

}

//Acivate a display according to i

PORTB=~(1<<i);

//Write the digit[i] in the ith display.

SevenSegment(digits[i],0);

}