Component

What it Does

Uses

Seven Segment Display

Ammeter

Measures current in amps or milliamps or microamps.

To measure the current passing through a device, connect the ammeter in SERIES with the device. Connecting an ammeter across a power supply or battery will damage the meter.

A logic gate. Both/all inputs of this logic gate must be on for the output to be on.

Q = A.B

Blocking/passing a signal, decision making, binary arithmetic, many more ...

Antenna

Sends or receives electromagnetic waves. Also commonly called an aerial.

Half wave dipole
Quarter wave vertical
Yagi
Parabolic dish (satellite).

• Converts a radio frequency alternating current into electromagnetic waves. (Transmitting)
• Converts electromagnetic waves into an alternating current (Recieving)
• A good transmitting antenna is also a good receiving antenna.

Makes a signal weaker.

• The simplest type of attenuator is a potential divider.
• Signals also get weaker when they travel through wires, fibres or free space. This is also called attenuation.

• The clock signal that keeps the workings of a computer synchronised.
• Sound effects.
• Timing pulses for a counter or digital clock.

Avalanche photodiode

Detects single photons of light.
Exceptionally sensitive device.
Needs to be cooled for best performance.

Accurate light measurement, fibre optic telecommunications, detecting nuclear reactions.

Battery | Wikipedia

Buffer / Tristate Buffer a.k.a. Driver

Take a small input power and deliver a much larger output power. For example to drive many devices connected to the data bus in a computer.

• Voltage gain = 1
• Current gain can be large
• Power gain can be large

Bulb

An output transducer that converts electrical energy into heat and light. The current flowing in a thin tungsten filament causes it to become white hot. Not very efficient or reliable.

• Illuminating dark areas
• Signalling eg traffic lights, railway signals, break lights, indicator lights, many more ...
• The bulb resistance increases as it heats up

Capacitor

Stores energy in the form of an electric charge.

Capacitance is measured in Farads.

Charge is measured in Coulombs.

Voltage is measured in Volts.

Q = C V

• Coupling capacitor - blocks DC and passes AC.
• Decoupling capacitor - short circuit AC to ground. (gets rid of it).
• Filters - Capacitors pass higher frequencies more easily so low and high pass filters can be built.
• Tuned circuits.
• Time delay circuits.
• X_c is reactance in ohms
• X_C = 1 / 2 π f C
• Q = C V
• T = R C

Conductor

Usually wire or printed circuit board tracks. The diagram left shows wires joining (blobs) and a wire crossing.

• Allow a current to pass with negligible resistance (usually assumed to be zero).

Crystal

Mechanical oscillations of a quartz crystal produce an AC signal at the same frequency. AC signals also cause mechanical oscillations.

• Top quality filters.
• Very accurate and stable oscillators found in digital clocks.
• Controlling transmitter frequencies.
• Controlling the clock on computer motherboards.

DAC

Digital to Analogue Converter

Converts a stream of binary data into an analogue signal.

• mp3 player
• ipod
• cd music
• dvd video
• digital TV
• DAB radio

D Type Flip Flop

On the rising edge of the clock pulse, D is copied to Q (edge triggered)

• Data latch
• Binary counter
• Modulo N Counter
• Shift Register
• Serial/parallel data conversion

Darlington Pair

Two bipolar transistors combined to give a very high current gain.

The gain of the pair is equal to the product of the gains of each transistor.

• touch sensitive switch
• rain sensor

Diode

Passes current in one direction only.

• Converting AC into DC.
• Protecting circuits from power connected the wrong way round.
• Demodulating AM radio.
• Soaking up the back EMF spike when a current changes suddenly in an inductor such as a relay.

Electret Microphone

A microphone with a built-in MOSFET pre-amplifier.

An input transducer used to convert sound wave energy into an equivalent AC signal.

Fuse

A thin wire in a glass or ceramic tube melts if the current is too big.

The fuse wire melts if the current flowing is too big. This protects the more expensive parts (eg your home) from fire damage due to over-heating. Most students have, in a moment of idiocy, blown one or more multimeter fuses.

Half Adder

0 plus 0 = 0 (carry 0)
0 plus 1 = 1 (carry 0)
1 plus 0 = 1 (carry 0)
1 plus 1 = 0 (carry 1)

Here you can spot the AND and EXOR rules.

Heat Sink

Not normally shown on circuit diagrams.

A black metal block with a large surface area used to get rid of waste heat.

Rated in degrees per watt. (How many degrees the temperature will rise when one watt of heat is fed into the heat sink.)

Inductor

A coil of wire (sometimes with a ferrite (dotted lines) or soft iron (solid lines)core). This stores energy in magnetic field.

• Passes DC
• Passes low frequencies more easily than high frequencies.
• Blocks high frequency AC.
• Tuned circuits.
• Filter circuits.
• X_l is reactance in ohms
• X_L = 2 π f L

• Paper
• Most plastics
• Dry wood
• Glass
• Most fabrics

Integrated Circuit (IC) on Wikipedia

Thousands of types.
Most have no symbol.

A wafer of semiconductor (usually silicon) with many components constructed on the wafer.

• All analogue and digital microchips including advanced central processing units (CPU) for computers. These can have many millions of transistors built onto one chip.

Latch

A logic circuit that is able to remember the most recent event.

The RS Flip Flop (left) is the simplest latch.

• D Type Flip Flop
• Counting
• Shift Register
• Serial to parallel conversion
• Input data latching
• Output data latching

LDR

A light dependent resistor.

• In the dark, the resistance is high
• In bright light, the resistance is low
• Used to measure light intensity.

LED

A diode that glows when current is flowing. The usual maximum allowed current is 20 mA. The voltage across a lit LED is about 1.8V.

• Indicator lights
• Cycle lighting
• Car brake lights
• Traffic lights
• Display screens

Microphone

An input transducer used to convert sound wave energy into an equivalent AC signal.

• Sound recording
• Intercoms
• Telephone mouth piece

• small
• reliable

• Clean up digital signals to correct the pulse timing.
• Provide a time delay to allow an alarm to be reset.
• Build a circuit where the output voltage is proportional to the input pulse frequency.

MOSFET

See Transistor (Field Effect)

• Send hundreds of phone calls down one cable (e.g. transatlantic cable).
• Allow many computers to share one network.

NAND

A logic gate. Both/all the inputs must be on for the output to be off.

Used in gate arrays, flip flops and very commonly in many logic circuits.

Neon Bulb

A gas discharge lamp used as a mains power-on indicator. The current must be limited with a resistor or sometimes with an inductor. Pure neon glows orange.

• Power-on indicator
• Fluorescent lights
• Advertising signs

NOR

A logic gate. Both/all the inputs must be off for the output to be on.

Used in gate arrays and very commonly in many logic circuits.

NOT

One of the simplest logic gates.

Used to invert a signal. 0 becomes 1 and 1 becomes 0.

Operational Amplifier

A versatile and easy to use analogue amplifier chip.
Ideal properties ...
Gain = infinity
Input resistance (impedance) = infinity
Output resistance (impedance) = zero
Input offset voltage = zero
Gain bandwidth product = infinity

• Inverting amplifier
• Non inverting amplifier
• Summing amplifier
• Voltage Follower
• Comparator
• Schmitt trigger
• Filter circuits (low pass, band pass, high pass)
• D to A Converter (DAC)
• Lots of other stuff

OR

A logic gate. Both/all the inputs must be off for the output to be off.

Q = A + B

Very commonly used in many logic circuits.

Oscilloscope

Gives a graphical display of AC signals in circuits.

Used to measure voltage, pulse duration, wave period and wave shape.

PIC

Programmable Integrated Circuit

The diagram (left) is an example. There are many different pin-outs.

Software is used instead of hardware to make very versatile sub-systems. The same pic chip can be programmed in many different ways to solve different problems.

Photodiode

A diode that generates power when light shines on it. If reversed biased, the leakage current increases when light shines on it.

• Solar panels
• Photo detectors/light meters
• Infra-red dectectors in remote controls

Potential Divider

V₁ / R₁ = V₂ / R₂

V₂ = V_s R₂ / (R₁ + R₂)

• Set a voltage to a fixed value between the negative and positive supply voltages.
• Set an adjustable voltage if a variable resistor is used.
• Set a voltage that depends on one of the resistor values. This resistor could be light or temperature dependent.

Potentiometer

A three pin resistor. The centre pin connects a slider to a resistive track allowing the resistance to be adjusted.

• Voltage control
• Volume control
• Tone control
• Light dimmer

A measure of the amount of energy produced per second. This could be wanted energy like sound or light or unwanted waste energy usually in the form of heat.

• Energy is measured in Joules
• Power is Joules per Second
• Power is measured in Watts
• P = I V
• P = V² / R
• P = I² R

RCD

Link

A mains supply safety device. Residual Current Device. Better than a fuse because it also protects against current leakage through faulty insulation.

• Trips the power off if the current into the device is not exactly balanced with the current coming out.
• Trips the power off if the total current is too great.

Rectifier

A diode used to convert AC to DC in a power supply.

• Convert AC to DC

Reed Switch

A small switch encased in a glass tube. The switch is activated with a magnet.

• Mechanical position sensing
• Burglar alarms - if a door is opened the switch opens and triggers the alarm.

Relay

An electromagnet that operates a switch.

NO = Normally open

NC = Normally closed

Com = Common connection

• Small currents can be used to activiate the relay. The relay switches large currents.
• The ignition key in a car operates a relay used to turn on the car starter motor.

Resistor

A device that allows a limited or reduced current to pass.

• Control or limit the current flowing in a circuit.
• Set the potential in a circuit (two resistors needed).
• Limit the current in a circuit to a safe level.
• Ohm's Law
• R = V / I
• V = I R
• I = V / R

Semiconductor

No symbol

Very pure Silicon, Germanium or Gallium Arsenide. By adding carefully chosen and very small amounts of impurities (called doping) many interesting devices can be manufactured.

• Diodes (all types)
• Bipolar transistors
• Field effect transistors
• Analogue ICs
• Digital ICs
• LEDs
• Photodiodes and LDRs

Schmitt Trigger

The turn-on voltage is NOT the same as the turn-off voltage.

This behaviour is often combined with comparator behaviour.

• Remove noise from digital signals.
• Add hysteresis - for example to turn on street lights when it is quite dark but to turn them off again when it is much lighter.

Speaker

An output transducer used to convert AC signals into equivalent sound waves.

Any device that reproduces sound with reasonable quality. Radio, sound system, HiFi, earphones, telephone earpiece.

Superconductor

No symbol

Specialised materials. At very low temperatures, they conduct with absolutely no resistance.

• Huge magnets
• Power transmission
• Measurement devices.

Switch

• Single pole single throw
• Double pole single throw
• Single pole double throw
• Double pole double throw

Tachometer - Shaft Encoder

No symbol

Used to count pulses from a sensor connected to a rotating shaft.

Used to measure revolutions per minute (RPM)

Thermistor

Temperature Dependent Resistor.

Note the similarity to a varistor. Always label this component clearly.

• High resistance at low temperatures
• Low resistance at high temperatures
• Used for measuring temperature

• movement sensors

Transducer

Many different symbols

Any device that converts energy from one form to another.

• Input transducers mostly measure something such as light intensity, temperature, movement or sound waves.
• Output transducers typically produce sound, light, heat or movement.

Transformer

Two coils of wire coupled together magnetically. An alternating current in one coil induces a similar alternating current in the second coil.

The magnetic coupling can be improved greatly by using a soft iron laminated core, a ferrite core, ring or toroid.

• Step down transformer to convert 230 or 110 volt mains down to 5 or 12 volts for typical electronic circuits.
• Step down transformer to convert kilovolt power lines down to the lower voltages needed for domestic supplies (230V or 110V).
• Step up transformer to convert the lowish voltage from power station generators up the the very high voltages needed for efficient power lines across the country.
• Isolating transformers that allow AC to pass but isolate any DC voltages.
• Coupling radio frequency circuits together in transmitters and receivers.

Transistor (Bipolar)

A three pin semiconductor. A small current in the base controls a much larger current flowing in the collector and emitter.

• Amplifiers
• Current controlled switches
• Astable circuit
• Bistable circuit
• Schmitt trigger

Transistor
(Field Effect)

MOSFET

A three pin semiconductor. A small voltage in the gate controls a much larger current flowing in the source and drain. The FET has a very high input impedance.

• Amplifiers
• Radio frequency amplifier
• Voltage controlled switches
• Astable circuit
• Bistable circuit
• Schmitt trigger
• Sensitive measuring equipment
• Low noise audio /radio frequency preamps

Varistor

A voltage dependent resistor used to get rid of voltage spikes on power supply lines.

Note the similarity to a thermistor. Always label this component clearly.

• Surge supressors

Voltage Follower

• Voltage regulator
• Audio power amplifier using MOSFETS as source followers

Voltmeter

Used to measure the voltage ACROSS a device.

Voltage is measured in Volts.

Connect the voltmeter in parallel with the device to be measured. Unlike an ammeter, a voltmeter can be connected across a power supply.

XOR

A logic gate. If the inputs are equal, the output is off.

Very commonly used in many logic circuits. Used to add binary digits. Used extensively in computer graphics processing.

Zener diode

A diode that is intentionally used in its breakdown region. This occurs at an exact voltage.

• The zener diode is used as a voltage reference in stabilised power supplies and measuring equipment.