In the earlier tutorials we saw how to interface the Leds to Atmega32 and wrote the code to blink, generate up counter, ringcounter etc. How ever the leds cannot be used to display any user information like numbers, char's etc. To display numeric values we can use seven segment displays.

In this tutorial we will interface a seven segment to ATmega32 and display a single digit hex counter(0-F). Later same will be extended to multiplex 4 seven segment displays to generate a 4-digit counter.

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1 Seven Segment Display
2 Hookup
3 Code
4 Video Tutorial
5 Downloads

Seven Segment Display

fig 1: Basic 7 segment Display

Well, the name 7 segments implies there are 7 LED segments arranged as shown in figure 1. After LEDs, these are the easiest interfaces to a microcontroller. There is also a decimal point or dp. It is used when decimal digits like 5.1 etc are displayed.

Applications

Seven segment are widely used in applications where digits[0-9] are required to be displayed.Although they also display letters A to F as shown in figure(2) simulation. This is a very simple and convenient way to display numbers in a bright fashion.

Form Factor

Sizes:They come in various sizes; 0.28”, 0.3”, 0.32”, 0.36”, 0.39”, 0.4”, 0.5”, 0.56”, 0.6”, 0.8”, 1.0”, 1.2”, 1.5”, 1.8”, 2.0”, 2.3”, 3.0”, 4.0”, 5.0”, 7.0”)
Colors: and varied colors too; Red, Green, Yellow, Orange, Blue, and White.

Working

fig 3:Common Cathode Display

fig 4: Common Anode 7 segment

Since these are basically LEDs arranged as a group they can either have anode in common or cathode thus they are named as Common-Anode/Common-Cathode displays.

Common Cathode: In this type of segments all the cathode terminals are made common and tied to GND. Thus the segments a to g needs a logic High signal(5v) in order to glow.This is shown in figure(3).
Common Anode: In this type of segments all the anodes terminals are made common and tied to VCC(5v). Thus the segments a to g needs a logic LOW signal(GND) in order to glow.This is shown in figure(4).

Hookup

Interfacing Seven Segment Displays with AVR bb.png

Code

	#include <avr/io.h>
	#include <util/delay.h>

	#define SegOne 0x01
	#define SegTwo 0x02
	#define SegThree 0x04
	#define SegFour 0x08



	int main() {
	char seg_code[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e};
	int cnt, num, temp,i;

	/* Configure the ports as output */
	DDRB = 0xff; // Data lines
	DDRD = 0xff; // Control signal PORTD0-PORTD3

	while (1)
	{
	for (cnt = 0x00; cnt <= 9999; cnt++) // loop to display 0-9999
	{
	for (i = 0; i < 100; i++)
	{
	num = cnt;
	temp = num / 1000;
	num = num % 1000;
	PORTD = SegOne;
	PORTB = seg_code[temp];
	_delay_ms(1);

	temp = num / 100;
	num = num % 100;
	PORTD = SegTwo;
	PORTB = seg_code[temp];
	_delay_ms(1);

	temp = num / 10;
	PORTD = SegThree;
	PORTB = seg_code[temp];
	_delay_ms(1);

	temp = num % 10;
	PORTD = SegFour;
	PORTB = seg_code[temp];
	_delay_ms(1);
	}
	}
	}
	}