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Low Frequency Two LED Light Blinker Oscillator

E L E C T R O N I C D E V I C E S A N D C I R C U I T S

E C S e m e s t e r - 3

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Contents:

1. Introduction2. Components used3. Function of components4. Circuit Diagram5. How to connect the circuit6. How it works7. Result8. Applications

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1. Introduction

The Transistor used along with the capacitor allows the LEDs to flash as per given timing sequence.

Hence the LEDs flash only one at a time.On changing the value of capacitors the timing

sequence changes.This circuit is a type of square wave oscillator.

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2. Components used

I. 2N2222 NPN Transistors 2II. Diodes 2III. 470 ohm resistors 2IV. 10k resistors 2V. 100 µF capacitors 2VI. LED 2VII. 9V Battery 1VIII. Connecting wires --IX. PCB 1

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3. Function of Components

2N2222 NPN Transistors are high speed switching Transistors.

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Different Transistors pins

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Function of Components…(2)

Diodes used in the circuit allow the flow of current only in one direction.

470 ohm resistors decrease the current going to the LEDs so they do not overload.

10k ohm resistors decrease the current and maintain the circuit in stable condition.

100 µF capacitors get charged when the current is flowing to provide constant current to transistor.

LEDs work only in forward bias. 9V battery is used to supply power to the circuit.

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4. Circuit Diagram

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5. How to connect the circuit

The first thing is the battery connector. It has two wires one red and one black. Of course the red is positive and the black is negative. The red connects to two wires, one goes to the resistor R1 and the other goes to R2.

Notice that at ground the both emitters of transistors Q1 and Q2 connect there, as well as both base resistors R3 and R4. They are all connected to the same common point or ground.

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How to connect the circuit…(2)

At this point, we will look at only one half of the schematic since both halves are identical. On the left side, the other end of R1 connects to LED diode D1's anode and D1's cathode connects to the collector of transistor Q1. Then Q1's emitter goes to ground.

Now look at Q1's base. It connects to three parts, R3,D3 and the other is C1. R3 and D3's anode connect to ground. The other end of C1 connects over to transistor Q2's collector.

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6. How it works

When the battery is connected both capacitors C1 and C2 begin to charge through the diodes and the base resistors R3 and R4 This will begin building a positive voltage on the transistor bases but because not all the parts will be exactly identical, one transistor will turn on before the other.

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How it works…(2)

As soon as one turns on the collector of that transistor will pull down toward ground completing the circuit through one of the LED's. That LED will light because it's cathode is pulled to ground through the transistor but look closely and you will see that capacitor connected to that diode will begin to discharge back to ground. This will place a positive voltage on the opposite transistors base and turn on that transistor.

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How it works…(3)

Now that action will cause a positive voltage to be applied to the other transistor's base turning it back on again which will cause the second transistor to turn on again and so on over and over again. Diode D3 and D4 discharge the capacitors C1 and C2 between cycles so they are ready to charge again on the next cycle.

The flash rate is determined by the value of R3, R4 and C1, C2.

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7. Result

Due to constant charging and discharging of capacitors, the LEDs go on constantly blinking.

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8. Application

Railroad crossing signal.Safety blinker for bicycles, etc.Christmas decorationsBlinkers to locate items in the dark.

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Members Involved

1. RATHOR VIJENDRASINGH 130170111092

2. RUDRA PAVAN 130170111095

3. RATHAVA JAYDEVSINH 130170111091

PPT available at: bitly.com/led-blinker