1. David Smith1 S.G. Electronics Revision Lesson

2. David Smith2 Introduction Electronic systems have 3 parts Input Process Output There are 2 types of systems: Analogue Digital

3. David Smith3 Output Devices These turn EE EE into some other form Analogue Motor, Bulb, Loudspeaker Digital LED, Relay, Solenoid

4. David Smith4 Input Devices 2 main types Change the size of the input voltage Switch, Capacitor, LDR, Thermistor and

5. David Smith5 Input Devices Energy Changers Thermocouple, Microphone Solar Cell

6. David Smith6 LDR As Light Intensity Increases Resistance Decreases

7. David Smith7 Thermistor As Temperature increases the resistance decreases

8. David Smith8 Capacitors Store Charge V –t Provide timing delays

9. David Smith9 Voltage Dividers VsVs 0 V R1R1 R2R2 V out

10. David Smith10 LDR in Voltage Divider As light increases, resistance of LDR decreases, voltage across it decreases, V out

11. David Smith11 Thermistor As temperature decreases, resistance of thermistor increases,voltage across thermistor increases, V out decreases V out

12. David Smith12 Capacitor charges up V out increases V out V s

13. David Smith13 Switches When switch is closed V out is low V out + 5 V

14. David Smith14 Process Devices Analogue : Amplifier Digital : Transistor Logic Gates

15. David Smith15 NPN Transistor V be > 0.7 V Transistor is switched on Collector Base Emitter

16. David Smith16 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

17. David Smith17 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

18. David Smith18 Capacitor charges up V c increases V be increases V be > 0.7 V transistor switches on Current flows through LED lights up Closing switch discharges capacitor / resets system Alarm Circuits

19. David Smith19 Logic Gates Digital Devices And Gate Or Gate Not Gate

20. David Smith20 And Gate A BOutput 001 100 010 111

21. David Smith21 Or Gate ABOutput 000 101 011 111

22. David Smith22 Not Gate InputOutput 0 1 1 0

23. David Smith23 Clock Pulse Generator Capacitor charges up,V c increases Input to NOT changes from 0 to 1 Output changes to 0, (led on ) Capacitor discharges,V c decreases Input to NOT changes from 1 to 0 Output changes to 1, (led off ) Process repeats

24. David Smith24 Amplifiers Analogue Process Device Frequency unchanged V in V out

25. David Smith25 Amplifiers in CD players amplify power

26. David Smith26 S.G. ELECTRONICS Now try the Revision Questions