GCSE Electronic Products

Revision Flashcards

555 timer

•8 pin Integrated Circuit (I.C.)•Analog•can be used as an astable or monostable•Low cost

Monostable(the egg timer)

•Has a single (mono) stable state• when it is timing

•The output is normally off

Pin 2 = Trigger

• The trigger sets the timer going

• Timer starts when trigger is < 2V

• Connects to a 10K pull-up resistor

Pull-up resistor

• Pulls the voltage up on a wire to supply voltage

• Makes a “nice” logic high

Pull Down Resistor

• Pulls the voltage on a wire down to 0V

• Gives a “nice” logic 0

Pin 6 = Threshold• Detects when the bucket

(capacitor) is 2/3rds full

• The capacitor fills up through a resistor

• Time to fill to 2/3rds full = Resistor Value x Capacitor Value (T = RC)

Pin 7 = discharge

• Empties the bucket (capacitor)

Astable(The “flasher” circuit)

• Has no stable states

• Keeps on flashing forever

• Number of flashes per second = frequency

• Automatically triggers

The Op-Amp• - input = inverting

• + input = non-inverting

• used as an inverting amplifier or a comparator

• An analog device

• A 741 I.C. is an example of an op-amp

Inverting

• Means it turns the signal upside down

Gain• The ability of a device

to make a signal bigger

• Op-amps have huge “open loop” gain

• Transistors also have gain

Feedback• Gain can be reduced by

using feedback

• Some of the output is taken away and added to the input

• We use resistors to do this

Comparator(Which input is bigger)

• If “+” is bigger than “-” we get a logic 1

• If “+” is smaller than “-” then we get a logic 0

• A simple analog to digital converter

+ -

Ohms Law

• As resistance increases, current decreases

• As resistance increases, voltage increases

Sources of power

P.I.C.(Peripheral Interface Controller)

• Digital• A mini-computer in a

single Integrated Circuit• Programmable using

flowcharts• Can be programmed many

times• Remembers program even

when the power is off

Diode(A one way valve)

• Current flows from anode to cathode

• Prevents current flowing the wrong way

• Protects circuits if the power supply is connected up wrong

Transducer(A device for converting energy

from one form to another• Motor – converts electrical

energy to kinetic energy• LED – converts electrical

energy to light• Microphone - converts

sound energy to electrical energy

Transducer Drivers(Things that provide power to output transducers)

• Bipolar Transistors• FET’s• Darlington Pairs

Tolerance

• The amount of “spread” in a components value

• 100Ω and 10% tolerance gives a spread between 90Ω and 110Ω

E12 Series

• The values that 10% tolerance resistors are made in to avoid value overlap

• 10, 12, 15, 18, 22 etc• 100, 120, 150, 180 etc

Polymorph – Smart Material

• Used to rapidly model complex shapes

• Granules put in hot water turn solid and can be immediately shaped

+

clock

• A digital signal that has a regular repeating on/off pattern

• Often generated by an astable

• Used by PICs & counters

HIPS

• Plastic material used for vacuum forming

• Available in different colours

• Used to make complex 3d shapes

• Boxes must have angled sides to get the mold out

Breadboard

• Used to model circuit using real component

• No soldering• Easy to change

connections• Components can be re-

used

CAD(Computer Aided Design)

• Testing by simulation

• Links to CAM (Computer Aided Manufacture)

• Easy to share designs with others and keep track of changes

• Making changes is a quick & easy process

Latch Circuit• Can be made using a

thyristor

• Can be made with NOR or NAND gates

• When activated, stays activated until reset– Remembers that it has

been activated

Thyristor• Used in latch circuits

• A pulse on the gate causes current to flow from Anode to Cathode until reset

• Reset by making the Anode voltage the same as the Cathode

Potential Divider

• A circuit for dividing voltages

• Voltage splits based upon the ratio of two resistors

Schmitt Trigger

• A type of circuit used to remove switch bounce

Thermistor• Device for measuring

temperature

• As temperature increases, resistance decreases

• Often used as part of a potential divider

LDR(Light Dependent Resistor)

• As light increases, resistance decreases

• Often used as part of a potential divider

Multimeter

• Device for measuring:– Current– Voltage– Resistance

• Has red & black probes

The 3 R’s(Helping The Environment)

• Reducecut the materials you use

• Reusemake use of existing products

• Recyclestop the product going to landfill when obsolete

Resistors• Measured in Ohms

(Ω)

• Used to reduce current

• Colour bands indicate the value

Integrated Circuits

• Pin 1 is to the left of the notch

• Lots of components on a single piece of silicon

• Examples are:– PICS– 555’s– 741’s

Switch Bounce

• A problem with mechanical PTM & PTB switches

• One press of the switch generates more than one pulse

AND Gate

• Both inputs must be at logic 1 to get a logic 1 out

• A = 1 AND B= 1

OR GATE

• Either one of the two inputs can be at logic 1 to create a 1 on the output

• A=1 OR B=1

Relay

• A device that allows one circuit to turn on another circuit that works at a different voltage

• Uses electro-magnets

Variable Resistor

• Used for– volume controls

– Changing astable frequencies

– Changing mono-stable time periods

4017• Output 0 is on• When a clock pulse is

received:– Output0 turns off– Output1 turns on

• On next clock pulse– Output1 turns off– Output2 turns on

SPDT SWITCH(Single Pole Double Throw)

• One circuit• Two positions• Three pins• Two different sets of

components can be switched into one circuit

Life Cycle Analysis

• What happens to a product when it is disposed of:

– Reused in a new product

– Recycled– Goes to landfill

Multipliers

1,000,000,000 = 1G = 1 x 109

1,000,000 = 1M = 1 x 106

1,000 = 1K = 1 x 103

1 = 1 = 1 x 101

0.001 = 1m = 1 x 10-3

0.000,001 = 1µ = 1 x 10-6

0.000,000,001 = 1n = 1 x 10-9

0.000,000,000,001 = 1p = 1 x 10-12

Units of MeasureMeasurement Unit Symbol

Resistance Ohms Ω

Capacitance Farads F

Voltage Volts V

Current Amps I

Power Watts W

Time Seconds S