Physics and Electronics

Electronic systems Electronic systems are made up of 3 parts: 1)An INPUT SENSOR – these detect changes in the environment Examples: 3) An OUTPUT DEVICE – these are controlled by the processor Examples: 2) A PROCESSOR – these decide what action is needed Examples:

Logic gates Logic gates are the basics behind any kind of processor. There are 3 that you need to know : NOT gate – “the output is NOT what the input is” AND – “the output is on if A AND B are both on” OR – “the output is on if A OR B are on” InputOutput Input AInput BOutput Input AInput BOutput

Logic gate symbols NOT gate: AND gate: OR gate:

Some problems to solve The pump on a central heating system is switched on at room temperature if the system is switched on (with the slide switch). When the temperature rises the pump needs to be switched off. Design a circuit that will sound a buzzer if the temperature of a hot radiator falls during the day ONLY. Include a test switch to check the operation of the buzzer. Design a circuit for a gardener that will warn them of cold conditions at night. The alarm should be able to be switched off.

Relays Circuits such as those containing logic gates only take very ______ currents. These circuits may be needed to operate a device that takes a much _____ current, e.g. a _________. To do this the circuit would need a RELAY switch, a device made of an _______ that can operate a switch. A relay switch is activated by the small current and the switch part is placed in the circuit needing a large current: Symbol for relay: Words – motor, larger, electromagnet, small M

The Resistor Colour Code We would use this to determine the value (in  ) of a resistor: % % % 331k 4410k 55100k 661M 7710M Significant figures Multiplier Tolerance (no band = 20%) E.g this resistor would have a value of 42 x 10 = 420  and a tolerance of 5%

Drawing electronic circuits 12V 0V V This voltmeter will read 12V V IN 0V This bulb and resistor are in parallel

Drawing electronic circuits 1) Two resistors in series 4) An ammeter measuring the current through a resistor 3) A voltmeter measuring the voltage across two bulbs in series 2) Two resistors in series with one bulb in parallel V IN 0V V IN 0V V IN 0V V V IN 0V A

Potential Dividers 0V V IN V OUT 0V R1R1 R2R2 (R 1 + R 2 ) V IN x (R 2 ) V OUT The Potential Divider equation:

Some example questions 0V 12V V OUT 0V 100  0V 1.5V V OUT 0V 50  45  0V 50V V OUT 0V 10  75  0V 3V V OUT 0V 75  25 

Practical applications 0V V in V OUT Here’s a potential divider that is used to control light-activated switches… When the light intensity on the LDR decreases its resistance will ________. This causes V OUT to _______ so the processor and output will probably turn _____. The variable resistor can be adjusted to change the ________ of the whole device. Words – decrease, sensitivity, increase, off

Transistors A transistor acts like a switch: Base Collector Emitter When a SMALL current flows through the base- emitter part of the transistor a different current is switched on through the collector- emitter part.

A light dependent switch 6V 0V Power supply Output device

A light dependent switch 1)When the light on the LDR decreases its resistance _________, which will decrease the ________ across the variable resistor 2)This will cause V OUT to ____. The____ gate will recognise this as a “0” and convert it into a “1”, i.e. a current will flow into the resistor 3)The resistor limits the amount of current flowing into the transistor, to avoid __________ it 4)When the transistor detects the current at its _____ it will “switch __” the collector-emitter current 5)A small current will then flow through the _______ 6)The relay will then switch on a _____ current in the output circuit 7)The “reversed biased” diode is also placed in the circuit to act as a “_______” to prevent current flowing back into the transistor when the relay is switched _____ Words – base, buffer, on, increases, damaging, relay, off, larger, voltage, drop, NOT

A light dependent switch 6V 0V We could modify this circuit (if we wanted to…) 2) Adjust this resistor to vary the sensitivity 1) Swap these two around and the output will now switch on when it becomes LIGHT, not when it becomes dark

The Capacitor A capacitor is a device that can store charge (it has a “capacity”). It is basically made of two plates: …or… Charge builds up on these plates and the voltage between them increases until it reaches the supply voltage.

Charging and discharging a capacitor P.d. across capacitor Time P.d. Time P.d. Time Increase resistance or capacitance

Time delay circuits 6V 0V Power supply Output device R

Time delay circuits “1” 6V 0V Power supply Output device R

Time delay circuits 1)When the switch is closed the capacitor is being short circuited so no charge builds up on it 2)This means that the input to the NOT gate is __, so the output is 1 and the output device is ___ 3)When the switch is released the capacitor starts to ________ up 4)When the voltage across the capacitor reaches a certain level the input to the NOT gate becomes __ so its output is 0 5)This means that the output device is now switched ___ 6)To INCREASE the amount of time taken to switch the device off you could: 1)Increase the _________ of the capacitor 2)_________ the resistance of the resistor R Words – charge, 1, capacitance, increase, 0, off, on

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