[DIY] The Design Of Multiplexed Seven Segment Counter

Two digits multiplexed common cathode seven segment displays are  connected to PORT C of the the MCU. Segments “a” through “g” are connected to PC0 through PC6respectively. The cathode of digits 1(tens) and 2(units) are connected to PD0 and PD1 respectively. The MCU extracts the ten and the unit digits, sends them to the seven segment display and activates the appropriate digit by pulling its cathode low. This happens very fast that it appears to be continuous to the eyes.Two buttons are connected to PB0 and PB1 through 10k pull down resistors.

The button at PB0 is used to increase the count while PB1 decreases the count. The circuit is designed to respond to a single button press at a time (a button must be released before it or another button is pressed).

The circuit diagram(captured from Proteus) is shown below. Vcc and ground connections are not shown but must be included to make the MCU work.

The C source code (well commented) is shown below.

/**************************************************************************

Title: Seven segment display

Version: 1.0

Target MCU: ATMEGA 16

Crystal: 1MHz

IDE/Compiler: AVR Studio 4/WinAVR

www.microscale-embedded.com

Date: August, 2011

**************************************************************************/

#include <avr/io.h>

#include <util/delay.h>

#define seven_segment PORTC

#define increase   PINB&(1<<PB0)

#define decrease PINB&(1<<PB1)

#define unit_select 0xED

#define ten_select 0xFE

uint8_t Seven_seg_code[10] = {0x3f,0×06,0x5b,0x4f,0×66,0x6d,0x7d,0×07,0x7f,0x6f};

//uint8_t decode(int);  //decode funtion declared

int main()

{

int count, status, status1;        //variable to hold count

DDRC=0xff;        //PORT C configured as output

DDRB=0×00;        //PORT B configured as input

DDRD=0xff;        //PORT D configured as output

PORTD = 0xff;

PORTC = 0×00;

//endless loop

while(1)

{

if(status&&status1)

{

if(increase)        //increase count if increase button is pressed

count++;

if(decrease)        //decrease count if increase button is pressed

count–;

}

if(count>99)            //rolls count back to zero(0) if it becomes

count=0;            //greater than 99

if(count<0)            //change count to 99 if it becomes negative

count=99;

int tens = count/10;

int units = count%10;

PORTD = unit_select;

seven_segment= Seven_seg_code[units];

_delay_ms(5);

PORTD = ten_select;

seven_segment= Seven_seg_code[tens];

//Checks key release after being pressed

if(increase)

status = 0;

else

status = 1;

if(decrease)

status1 = 0;

else

status1 = 1;

_delay_ms(100);    // a brief delay

}

return 0;

}

Editor’s Note: Microscale Embedded contributed this piece.

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