S.G. Electronics

1
S.G. Electronics

• Revision Lesson

2
Introduction

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

3
Output Devices

• These turn EE into some other form
• Analogue
• Motor, Bulb, Loudspeaker
• Digital
• LED, Relay, Solenoid

4
Input Devices

• 2 main types
• Change the size of the input voltage
• Switch, Capacitor,
• LDR, Thermistor
• and

5
Input Devices

• Energy Changers
• Thermocouple, Microphone
• Solar Cell

6
LDR

• As Light Intensity Increases Resistance Decreases

7
Thermistor

• As Temperature increases the resistance decreases

8
Capacitors

• Store Charge
• V
• t
• Provide timing delays

9
Voltage Dividers

• Vs

R1
Vout
R2
0 V
10
LDR in Voltage Divider

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

V out
11
Thermistor

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

Vout
12
Capacitor

• Capacitor charges up
• Vout increases

V s
V out
13
Switches

• When switch is closed
• V out is low

5 V
V out
14
Process Devices

• Analogue Amplifier
• Digital Transistor Logic Gates

15
NPN Transistor

• V be gt 0.7 V
• Transistor is switched on

Collector Base Emitter
16
Alarm Circuits

• Light Intensity decreases
• R ldr increases
• V ldr increases
• V be increases
• V be gt 0.7 V
• Transistor switches on
• Current flows through LED

17
Alarm Circuits

• Temperature increases
• R thermistor decreases
• V thermistor decreases
• V resistor increases
• V be increases
• V be gt 0.7 V
• Transistor switches on
• Current flows through LED
• Current flows through LED

18
Alarm Circuits

• Capacitor charges up
• Vc increases
• Vbe increases
• Vbe gt 0.7 V transistor switches on
• Current flows through LED
• LED lights up
• Closing switch discharges capacitor / resets
  system

19
Logic Gates

• Digital Devices
• And Gate
• Or Gate
• Not Gate

20
And Gate

• A B Output
• 0 0 1
• 1 0 0
• 0 1 0
• 1 1 1

21
Or Gate

• A B Output
• 0 0 0
• 1 0 1
• 0 1 1
• 1 1 1

22
Not Gate

• Input Output
• 0 1
• 1 0

23
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

24
Amplifiers

• Analogue Process Device
• Frequency unchanged

V in
V out
25
Amplifiers

• Amplifiers in CD players amplify power

26
S.G. ELECTRONICS
Now try the Revision Questions