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S.G. ElectronicsRevision Lesson

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Introduction

Electronic systems have 3 parts Input Process Output There are 2 types of systems: Analogue Digital

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Output Devices

These turn EE into some other form

Analogue

Motor, Bulb, Loudspeaker

Digital

LED, Relay, Solenoid

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Input Devices

2 main types

Change the size of the input voltage

Switch, Capacitor, LDR, Thermistor

and

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Input Devices

Energy Changers

Thermocouple, Microphone Solar Cell

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LDR

As Light Intensity Increases Resistance Decreases

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Thermistor

As Temperature increases the resistance decreases

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Capacitors

Store Charge V

– t

Provide timing delays

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Voltage Dividers

Vs

0 V

R1

R2

Vout

21

2SOUT R+R

R×V=V

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LDR in Voltage Divider

As light increases, resistance of LDR decreases, voltage across it decreases,

V out

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Thermistor

As temperature decreases, resistance of thermistor increases,voltage across thermistor increases, V out decreases

Vout

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Capacitor

Capacitor charges up Vout increases

V out

V s

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Switches

When switch is closed V out is low

V out

+ 5 V

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Process Devices

Analogue : Amplifier

Digital : Transistor Logic Gates

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NPN Transistor

V be > 0.7 V Transistor is switched on

Collector

Base

Emitter

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Alarm Circuits

Light Intensity decreases R ldr increases

V ldr increases

V be increases

V be > 0.7 V Transistor switches on Current flows through LED

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Alarm Circuits

Temperature increases R thermistor decreases

V thermistor decreases

V resistor increases

V be increases

V be > 0.7 V Transistor switches on Current flows through LED

Current flows through LED

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Capacitor charges up Vc increases

Vbe increases

Vbe > 0.7 V transistor switches on Current flows through LED LED lights up Closing switch discharges

capacitor / resets system

Alarm Circuits

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Logic Gates

Digital Devices

And Gate

Or Gate

Not Gate

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And Gate

A B Output

0 0 1

1 0 0

0 1 0

1 1 1

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Or Gate

A B Output

0 0 0

1 0 1

0 1 1

1 1 1

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Not Gate

Input Output

0 1

1 0

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Clock Pulse Generator

Capacitor charges up,Vc increases Input to NOT changes from 0 to 1 Output changes to 0 , (led on ) Capacitor discharges,Vc decreases Input to NOT changes from 1 to 0 Output changes to 1, (led off ) Process repeats

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Amplifiers

Analogue Process Device

Frequency unchanged

in

out

V

VGainVoltage =

V in V out

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Amplifiers

Amplifiers in CD players amplify power

in

out

P

PGainPower =

R

VP

2

=

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S.G. ELECTRONICS

Now try the Revision Questions