Interfacing ATMega32 To Seven Segment Display

Seven Segment Display (SSD) is a classical display device for low end digital electronic equipment. The programming for is very simple. It could represent numbers and some English letters.

It come with two terminology, common cathode type and common anode type. But deciding which type to use depends on the application. In this example, I take only common cathode type.

single digit seven segments display

Segment LED diagram

Since it made of seven LED segment, we just turn on any LED to display digit or letter. For example, turning on LED segment B and C make digit "1" to display.

In programming, they commonly use hexadecimal equivalent to the SSD output.

For the common cathode type display the hex code represent the digit from 0 to 9 and from A to F is shown below:

Each LED segment made of from LED, requiring around 2 V and ~10 mA of current. Typically, the digital output from microcontroller drives a voltage of +5V TTL. So we need to cut down the voltage from microcontroller to ~2 V via resistor.

Resistors are connected to cut down voltage output to common cathode SSD

In this example, I use a digital input from PD0 to count the event, and output the counting to the presented SSD.

Circuit diagram uses for simulation

Source Code:

#include <avr/io.h>
#define F_CPU 16000000UL
#include "util/delay.h"
//SET THE INPUT BUTTON FOR COUNTING
#define btnPressed ((PIND&0x01)==0)
int main(void)
{
    //SEVEN SEGMENT MAP FOR COMMON 
    //CATHODE TYPE SEVEN SEGMENT DISPLAY
    unsigned char ssd[16]={0x3F,0x06,0x5B,0x4F,0x66,0x6D,0x7D,
        0x07,0x7F,0x6F,0x77,0x7C,0x39,0x5E,0x79,0x71};
    unsigned char btnCount=0;
    DDRC=0xFF;    //PORTC IS FOR OUTPUT TO SEVEN SEGMENT
    DDRD=0xFE;  //PORTD PD0 IS USED FOR INPUT COUNTING
    PORTD=0x01; //SET PD0 TO HIGH FOR PULLING UP
    while (1) 
    {
        if (btnPressed) //CHECK IF PD0 IS PRESSED
        {
            btnCount+=1; //Increase The Counter
            _delay_ms(250);
            if(btnCount>15) btnCount=0; 
             //RESET COUNTER WHEN IT IS OVER 15
        }
        PORTC=ssd[btnCount];  //OUTPUT TO SSD
    }
}

Back to main tutorial page ATMega32 tutorials in C with Atmel Studio 7.

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