LIGHT EMITTING DIODE Interfacing tutorial

        Light Emitting Diodes (LED) is the most commonly used electronic components, generally for display digital states. Typical uses of LED's include alarm devices, timers and confirmation of user input such as a mouse click or keystroke, events etc. LED's are very cheap and easily available in a variety of shape, size and colors.

        89C51, which belongs to the family of 8051 series of micro-controllers  is very commonly used by a large community of hobbyist and engineers. Its simplicity and ease of programming with inbuilt features easily makes its position in the top preferred list of micro-controller for both beginners and advanced user.
To connect a led refer the methods of connection here

        You can use 10-15 mA as a safe LED current which will provide decent light intensity and conserve battery power. Determine the Series resistor using Ohms law with an excess voltage value and current value for LED. Red LED's generally need 1.5V to 1.9V to light any extra voltage must be dropped with a series resistor else the LED will draw extra current in an attempt to lower the supply voltage down to the 1.5V level. The typical supply voltage source for micro-controller is 5V.

Then, 5 - 1.7 = 3.3V of excess voltage.
Let’s design the LED to use 10mA
Ohms law Resistance R = V / I
3.3 / 10mA = 330 Ohms, Place a 330 ohm resistor in series with the LED.

Circuit Diagram

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Interfacing Switch and LED with 8051

Interfacing Switch and LED with 8051

            This article is meant for beginners in the field of micro-controllers  When I started with micro-controllers as everyone I also need to learn how to interface a switch with micro-controller.

A switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. A switch may be directly manipulated by a human as a control signal to a system, or to control power flow in a circuit.

A switch requires a pull-up or pull-down resistor to produce a definite high or low voltage when it is open or closed. A resistor placed between a digital input and the supply voltage is called a "pull-up" resistor because it normally pulls the pin's voltage up to the supply. 

Software Tools:

1.      RIDE Compiler (Evaluation version) 

2.      WINISP Down loader      (Free version ) 

Hardware:

1. P89C51

2. Push button switch

3. micro-controller board

Program:

#include<reg51.h>

sbit LED=P0^7; //port declaration

sbit SW1=P0^0;

sbit SW2=P0^1;

void main()

{

while(1)

{

if(SW1==0 || SW2==0) //if the SW1 or SW2 is pressed

{

LED=1;

}

else

LED=0;

}

}

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