David Smith1 S.G. Electronics Revision Lesson

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

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

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

David Smith5 Input Devices Energy Changers Thermocouple, Microphone Solar Cell

David Smith6 LDR As Light Intensity Increases Resistance Decreases

David Smith7 Thermistor As Temperature increases the resistance decreases

David Smith8 Capacitors Store Charge V –t Provide timing delays

David Smith9 Voltage Dividers VsVs 0 V R1R1 R2R2 V out

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

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

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

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

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

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

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

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

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

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

David Smith20 And Gate A BOutput

David Smith21 Or Gate ABOutput

David Smith22 Not Gate InputOutput

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

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

David Smith25 Amplifiers in CD players amplify power

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