Light Emitting Diode (L

7/29/2019 Light Emitting Diode (L

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Light Emitting Diode: LED


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What is an LED?

Light-emitting diode

Semiconductor

Has polarity


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LED: How It Works

When currentflows across adiode

Negative electrons move oneway and positive holes move

the other way


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LED: How It Works

The wholes existat a lower energylevel than the

free electrons

Therefore when a freeelectrons falls it losses energy


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LED: How It Works

This energy isemitted in a formof a photon,

which causes light

The color of the light isdetermined by the fall of the

electron and hence energylevel of the photon


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Inside a Light Emitting Diode

1. TransparentPlastic Case

2. Terminal Pins

3. Diode


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Kinds of LEDs


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How to Connect a LED:

Requires 1.5~2.5V and 10 mA

To prevent overloading, use resistor

470


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How to Connect a LED:


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Connect LED to BS2

LED is on whenP0 is high

LED is on whenP1 is low


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Connect Multiple LEDs to BS2

8 LEDs are connected to BS2 eachI/O pin (P0-P7) is allowed to sink6.25mA


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Case Study: Blinking LED


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Case Study: Blinking LED

Pbasic program to make an LED blink

output 0

Main:low 0pause 1000

high 0pause 1000goto Main

Make pin0 an output

Loop begins here

Turn LED on

Pause for 1 sec

Turn LED off

Pause for 1 sec

Go back to beginning ofloop


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Experiments

Flash an LED1. Single LED

2. Multiple LEDs

Traffic Light by use of LEDs

Documents

Light Emitting Diode (L