The document discusses interfacing output devices like LEDs and seven segment displays with microcontrollers. It provides information on LED and seven segment display characteristics and working principles. It also includes code examples for interfacing LEDs and seven segment displays with the AVR microcontroller family using C programming. Practical examples discussed are LED interfacing and seven segment display interfacing projects.

1. TECHVILLA
WWW.TECHVILLA.ORG.IN

2. OUTPUT DEVICES INTERFACING
• Hardware information.
• Different compiler information.
• PRACTICAL1 : LED interfacing.
• PRACTICAL2: SSD interfacing.
• PROJECT: microcontroller based led pattern generation

3. HARDWARE INFORMATION
• LEDs
• Seven segment displays.

4. LIGHT EMITTING DIODE

5. WHAT IS AN LED?
• An led is a pn junction opto-semiconductor that emits a monochromatic(single color)
light when operated in a forward biased junction.
• Instead of a filament they use a semiconductor diode which emits narrow-spectrum light.
• Depending on the composition & condition of the semiconducting material used
(Silicone, germanium), they come in either Infrared for sensing heat, Visible for every
day use, or Near-Ultraviolet for spotting stains at a crime-scene.
• An LED consists of a chip of semiconducting material that has been “doped” with
impurities in order to create a p-n junction.
• A p-n junction is basically a junction between an anode and a cathode.
• Current flows easily from the p-side to the n-side, but never in the reverse order.
• The wavelength and color of the LED depends on the band-gap energy of the materials
forming the p-n junction

6. WORKING PRINCIPLE

7. LED CHARACTERISTICS

8. LED CHARACTERISTICS
• Forward bias of approximately 1 volt is needed to give significant forward
current.
• The commercially used LED’s have a typical voltage drop between 1.5 Volt
to 2.5 Volt or current between 10 to 50 milliamperes.
• Series resistance is determined by the following equation.
• Rseries = (Vsupply – V)/I
• Vsupply – Supply Voltage
• V – LED forward bias voltage

9. SEVEN SEGMENT DISPLAYS

10. WHAT IS A SEVEN SEGMENT DISPLAY?
• A Seven-Segment Display (SSD) is simply a figure eight grouping of
LEDs [some include a decimal point (DP)].
• Each Segment is labeled (a) through (g).
• SSDs are available in two configurations
• Common Cathode (all LED cathodes are connected)
• Common Anode (all LED anodes are connected)

11. TYPES OF SSD

12. SEVEN SEGMENT DISPLAY CODES

13. SEVEN SEGMENT DISPLAY CODES

14. LED INTERFACING WITH AVR
• Leds require around 50mA,so we usually require a current-limiting
resistor.
• The resistance of the resistor is calculated using the well known
formula V=IR.

15. ATMEGA16 INTERFACING WITH LEDS

16. C PROGRAMMING
#include <avr/io.h>
#include <util/delay.h>
Int main()
{
DDRX = 0xFF; // x – can be PORTA/B/C/D
while(1) {
PORTX = 0xff; }
return 0;
}

17. SSD INTERFACING WITH AVR

18. C PROGRAM
#include <avr/io.h>
#include <util/delay.h>
Int main()
{
DDRX = 0xFF ; // x can be A,B,C or D
while(1) {
PORTA = 0b00110000; // display number 1
_delay_ms(1000); // delay 1 sec

19. PORTA = 0b01011011; // display number 2
_delay_ms(1000);
PORTA = 0b01001111; // display number 3
_delay_ms(1000);
PORTA = 0b01100110; // display number 4
_delay_ms(1000);

20. PORTA = 0b01110111; // Display letter A
_delay_ms(1000);
PORTA = 0b00111001; // display letter C
_delay_ms(1000);
PORTA = 0b01111001; // display letter E
_delay_ms(1000);
PORTA = 0b01110001; // display letter F
_delay_ms(1000);