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Electronic Components

I have been asked many times to create a list of common terms used in model railway electronics, and the product descriptions within this website, to explain what each component is and what it does. So if you are new to electronics and electronic circuitry here is a handy glossary of common used words and terms used.

If you hnotice any obvious ommissions, or any errors please let me know by using the contact us form.


555 Timer:
The 555 timer is still one of the most popular ICs used in electronic circuits. It is used in timer and multi-vibrator applications.


Alligator Clips:
Used to temporarily hold an electrical connection together for testing or soldering. Often made of nickel plated steel. Can be found with vinyl insulators.
Alternating Current:
An electric current that reverses direction on a periodic basis. It is widely used to transport power on power lines.
The ampere is the standard unit of measure of electric current. It is sometimes written as amp.
The maximum absolute value reached by a voltage or current waveform.
The anode of a device is the terminal where current flows in.
American Wire Gauge - a system of measuring wire size.


The width of the range or band of frequencies that an electronic signal uses on a given transmission medium. Here bandwidth is expressed in terms of the difference between the highest frequency signal component and the lowest frequency signal component.
A DC voltage source containing two or more cells that convert chemical energy to electrical energy.
The method of establishing predetermined voltages and/or currents at various points of a circuit to set the appropriate operating point.
Relating to a device capable of using two polarizations, such as a transistor that uses positive and negative charge carriers.
Bits per second:
A measure of data speed for the number of bits transmitted or received each second.
A thin plastic board full of holes used to hold components that are wired together. It is commonly used for prototyping and experimenting with circuit designs.
Bridge Rectifier:
A rectifier with four elements connected as a bridge circuit with direct voltage secured from one pair of opposite junctions when alternating voltage is applied to the other pair.


A bound or sheathed group of mutually insulated conductors.
The ability of a capacitor to store an electrical charge. The basic unit is a Farad.
A basic electrical component that stores an electrical charge for a short period of time, and then returns it to the circuit. Capacitors are made from two electrical conductors separated by an insulator. Common types of capacitors include tantalum, electrolytic, ceramic, and film capacitors.
Carbon film resistor:
Device made by depositing a thin carbon film on a ceramic form.
The cathode of a device is the terminal where current flows out.
Ceramic Capacitor:
A ceramic capacitor is a capacitor constructed of alternating layers of metal and ceramic , with the ceramic material acting as the dielectric.
Metal box or frame to mount components.
Chassis ground:
Earthing connection to a chassis.
A configuration of electrically or electro magnetically connected components or devices.
Circuit breaker:
An electrical switch whose main function is to protect a circuit from overcurrent by interrupting current flow when a fault is detected.
Circuit protection:
Devices that are designed to keep components safe in situations where an excessive amount of current is suddenly introduced to a circuit.
Closed Circuit:
An electric circuit providing an uninterrupted, endless path for the flow of current.
Closed Position:
Relates to the position of switches and the way the current can flow.
Abbreviation for complementary metal oxide semiconductor, a class of integrated circuits.
Cold Solder Joint:
A faulty joint in electric wiring which results from the application of insufficient heat at the joint. The solder merely covers the joint and is not physically attached.
A device used in an electric generator to convert the alternating current produced in the generator into direct current before the current is sent into an external circuit. It is basically a rotary switching device synchronized with the frequency of the alternating current. Commutators are also used in electric motors to switch currents in order to maintain magnetic polarities necessary to keep the shafts of the motors turning.
A material that allows the free flow of electric charge. Copper wiring is the most widely used electrical conductor.
A device that joins to other conductors and to the terminals of apparatus and equipment.
Occurs when a complete path for current exists.
Crocodile clips:
Another name for Alligator clips.
The amount of electric charge flowing past a specified circuit point per unit time.


Dead short:
Short circuit having zero resistance.
A circuit that responds to a particular coded signal while rejecting others.
Relating to devices or circuits that have outputs of only two discrete levels. Examples: 0 or 1, high or low, on or off, true or false etc.
A two terminal device that conducts in only one direction.
Dip switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family are usually groupings of small switches used as jumper blocks or small rotary type switches that require a tool to set.
Direct current (DC):
A type of current that only flows in one direction (unlike AC which periodically reverses direction).
Release of energy stored in either a battery or a capacitor.
D sub connector:
Devices that have a "D" look to the mating end. Items in this family will have either male pins or female sockets for contacts. The size and layout of the "D" shape will determine the number and type of contact used in the device.
Dual In Line Package:
Integrated circuit package that has two rows of connecting pins.
Dry cell:
DC voltage generating chemical cell using a non liquid (paste) electrolyte.


A flow of electrical charges such as electrons through a conductor.
Electrolytic Capacitors:
An electrolytic capacitor is a type of capacitor typically with a larger capacitance per unit volume than other types, making them valuable in relatively high current and low frequency electrical circuits.
A magnet consisting basically of a coil of insulated wire wrapped around a soft iron core that is magnetized only when current flows through the wire.
Electromotive Force:
Measured in volts, a force that exists between postive and negative charges.
An elementary particle which is the negatively charged constituent of ordinary matter.
An encoder is a device used to change a signal or data into a code.
Electrostatic discharge (ESD):
Electrostatic discharge is the form of current that is left within an insulating body after the power source is removed.


The standard unit of measure for capacitance.
Ferrite Core:
A device placed on cables and wires to reduce RF interference.
Fibre optic cable:
Cables that contain a glass or plastic thread enclosed within a jacketed material.
A protective device in the current path that melts or breaks when current exceeds a predetermined maximum value.
Fuse holder:
A device used to facilitate the easy insertion and removal of fuses in an electronic circuit.


An increase in signal power, voltage, or current by an amplifier, expressed as the ratio of output to input. Also called amplification.
A system to measure wire or tubing.
A conducting object, such as a wire, that is connected to such a position of zero potential.


Heat shrink tube:
Hollow tubes of woven material with both ends open. These tubes become smaller in size as they become warm. Most often used as insulation material when connecting wires together, these tubes can be used to group wires together, insulate items from mechanical wear, and much more.
A mass of metal that is added to a device for the purpose of drawing off and dissipating heat; used with power transistors and many types of metallic rectifiers. Also known as dissipator.
The standard unit of measure for inductance.
Hertz (Hz):
A unit of frequency, equal to one cycle per second; symbol. Abbreviated as Hz.
High Pass Filter:
A filter that blocks low frequencies and allows high frequencies to pass through.


Abbreviation for Integrated Circuit which is a microscopic array of electronic circuits and components that has been diffused or implanted onto the surface of a single chip of semiconducting material such as silicon.
Opposition that a circuit presents to electric current. It includes both resistance and reactance.
The property of an electric circuit or of two neighboring circuits whereby an electromotive force is induced by the process of electromagnetic induction in one of the circuits by a change of current in either of them. A device for introducing inductance into a circuit.
Infrared (LEDs):
Infrared is an invisible band of radiation at the lower end of the visible light spectrum. With wavelengths from 750 nm to 1 mm, infrared starts at the end of the microwave spectrum and ends at the beginning of visible light. Infrared transmission typically requires an unobstructed line of sight between transmitter and receiver.
A material in which an electronic charge does not flow freely and does not conduct the flow of electric current.
Integrated Circuit (IC):
An IC is a microscopic array of electronic circuits and components that has been diffused or implanted onto the surface of a single chip of semiconducting material such as silicon.
A device used to convert direct current into alternating current. Also, a type of logicgate with a single input.


A type of connector.
The unit of work and energy.
Jumper wire:
A length of insulated, stiff, single conductor wire with stripped ends bent at 90 degree angles commonly used with breadboards to make test circuits.


Key lock switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family use a key as an actuator which will turn along the center axis point but have a predetermined number of stopping positions. The key may or may not be removable at any number of these positions.
K Ohm:
One thousand ohms.


Light-emitting diode (LED):
A semiconductor diode that converts electric energy into electromagnetic radiation at a visible and near infrared frequencies when its pn junction is forward biased.
Circuit or device that prevents some portion of its input from reaching the output.
Relationship between input and output in which the output varies in direct proportion to the input.
Live Circuit:
Term used to describe a circuit or piece of equipment that is on and has current flow within it.
Logic Gate:
An electronic device that performs a logical operation on an input signal.
Low Pass Filter:
A filter designed to transmit electromagnetic frequencies below a certain value, while excluding those of a higher frequency.
A fitting to which wires can be attached.
A lumen is a unit of luminous flux. It is represented by the abbreviation lm. One lumen equals the amount of light emitted in a solid angle from a source that radiates to an equal extent in all directions.
A source drives a load. Whatever component or piece of equipment is connected to a source and draws current from a source is a load on that source.
Relationship between input and output in which the output varies in direct proportion to the input.


Metal film resistor:
A resistor in which a film of metal oxide or alloy is deposited on an insulating substrate.
Known as an MCU, a microcontroller is a type of microprocessor that can contain an entire Computer on a chip.
Metal oxide resistor:
A metal film resistor in which an oxide of metal (such as tin) is deposited as a film onto the substrate.
Metal Oxide Varistor (MOV):
A two electrode device having a voltage dependent nonlinear resistance; its resistance drops as the applied voltage is increased. Also known as voltage dependent resistor. Abbreviated as MOV.
Abbreviation for "metal oxide field effect transistor" also known as an "insulated gate field effect transistor). A field effect transistor in which the insulating layer between the gate electrode and the channel is a metal oxide layer.
Electronic test equipment that can perform multiple tasks. Typically capable of measuring voltage, current and resistance. More sophisticated modern digital multimeters also measure capacitance, inductance, current gain of transistors and/or anything else that can be measured electronically.
Multi segmant display:
A device made of several light emitting diodes arranged in a numeric or alphanumeric pattern. By lighting selected segments numeric or alphabet characters can be displayed.


Terminal that has an excess of electrons.
Negative charge:
A charge that has more electrons than protons.
Negative ion:
An atom having a greater number of electrons in orbit than there are protons in the nucleus.
Negative Ion enerator:
A negative ion generator is a device that uses high voltage to ionise or electrically charge air molecules. Negative ions, or anions, are particles with one or more extra electron, conferring a net negative charge to the particle.
Neon bulb:
Glass envelope filled with neon gas which when ionized by an applied voltage will glow.
A terminal, point or object with balanced charges. Neither positive or negative.
Neutral wire:
The conductor of a polyphase circuit or a single-phase three wire circuit that is intended to have a ground potential. The potential difference between the neutral and each of the other conductors are approximately equal in magnitude and equally spaced in phase.
Junction or branch point in a circuit.
A semiconductor to which doping material is added to increase the number of free charge carriers.
Normal closed:
Designation which states that the contacts of a switch or relay are closed or connected when at rest. When activated, the contacts open or separated.
Normally open:
Designation which states that the contacts of a switch or relay are normally open or not connected. When activated the contacts close or become connected.


The standard unit of measure for resistance.
Device used to measure electrical resistance.
Ohms Law:
The equation used to calculate voltage, current, resistance or power. The law states that the direct current flowing in a conductor is directly proportional to the potential difference between its ends. The equation is written as V = IR.
Open Circuit:
A circuit that is broken and current is unable to flow.
Terminal at which a component, circuit or piece of equipment delivers current, voltage or power.
Condition that occurs when the load is greater than the system was designed to handle.
Overload protection:
Protective device such as a fuse or circuit breaker that automatically disconnects a load when current exceeds a predetermined value.


Circuit board contact points.
Parallel circuit:
Circuit having two or more paths for current flow.
Passive component:
Component that does not amplify a signal. Resistors and capacitors are examples.
Angular relationship between two waves.
Photovoltaic Cells:
Formerly used exclusively in space, photovoltaic cells convert sunlight into electricity. Photo=Light; Voltaic=Electricity.
Movable connector that is normally connected into a socket or jack.
Term used to describe positive and negative charges.
In an active filter, a single RC circuit. A one pole filter has one capacitor and one resistor. A two pole filter has two RC circuits and so on.
Manually adjustable, variable, electrical resistor. It has a resistance element that is attached to the circuit by three contacts, or terminals. Also referred to as a pot.
Amount of energy converted by a circuit or component in a unit of time, normally seconds. Measured in units of watts. (joules/second).
Primary winding:
First winding of a transformer. Winding that is connected to the source as opposed to secondary which is a winding connected to a load.
Printed circuit board:
Insulating board containing conductive tracks for circuit connections.
A positively charged particle.
Prototyping Board:
A thin plastic board full of holes used to hold components that are wired together. It is commonly used for prototyping and experimenting with circuit designs and also referred to as a breadboard.
Proximity Sensor:
Devices designed to detect and respond to movement outside of the component but within the range of the sensor.
A short duration of current flow which rapidly alternates between high and low.
Pulse Width Modulation:
A method to control the speed of a motor by turning voltage on and off in rapid pulses. The longer the intervals, the faster the speed of the motor.
Push button switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family are turned on or off through the use of an actuator that is depressed into the units body.


Rectifier Diode:
A diode which is designed for a waveform that periodically reverses direction. They are often used in DC Power Supplies, and High Voltage DC power transmission systems.
Regulated power supply:
Power supply that maintains a constant output voltage under changing load conditions.
A measurement of the difficulty encountered by a power source in forcing electric current through an electrical circuit, and hence the amount of power dissipated in the circuit. Resistance is measured in ohms.
A device that responds to a small current or voltage change by activating switches or other devices in an electric circuit.
A basic electronic component that prevents the flow of electric current by producing a voltage drop between its terminals in accordance with Ohms law.
Reverse current:
Current through a diode when reverse biased. An extremely small current also referred to as leakage.
Rocker Switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family are turned on or off through the use of an actuator that rocks along a center axis. The depressed side of the actuator will be lower than the opposite side.
Rotary Switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family are composed of a turntable center actuator that has one or more decks (thin circular boards) of contacts.


Schematic diagram:
Illustration of an electrical or electronic circuit with the components represented by their symbols.
Schottky diode:
Also known as a "hot-carrier diode" or "surface barrier diode", a high speed diode that has very little junction capacitance.
Secondary Winding:
The output winding of a transformer that is connected to the load.
Single in-line package:
Package containing several electronic components (generally resistors) with a single row of connecting pins.
A material that behaves between a conductor and an insulator depending on the conditions. Silicon is a widely used semiconductor in electronics.
A sensor is a type of transducer. Since a significant change involves an exchange of energy, sensors can be classified according to the type of energy transfer that they detect.
Series Circuit:
A circuit in which current runs sequentially through each component.
Short Circuit:
An abnormal condition of relatively low impedance, whether accidental or intentional, between two points of different potential in an electric network.
Single Pole Double Throw Switch (SPDT):
A three-terminal switch or relay contact arrangement that connects one terminal to either of two other terminals.
Single Pole Switch:
A switch with only one input wire.
Slide Switch:
A switch with an actuator that slides forward and backward to turn the device on and off.
Surface Mount Device.
Solderless Breadboard:
A prototyping board that requires no solder to attach the components.
Devices that contain a metal cylinder core that moves in and out of the component based on the current flow through the device.
Solid Wire:
Wire consisting of a single strand.
A brief increase in voltage.
Static electricity:
The build up of an electric charge on the surface of an object. The charge remains in one area rather than flowing to another area.
Stepper Motor:
Devices designed to turn electricity into mechanical motion. These devices take digital pulses and convert them into incremental movements (steps) of a central shaft.
Stranded Wire:
A group of wires or combinations of groups of wires usually twisted together wrapped within an insulated outer.
Supply voltage:
Voltage provided by a power source.
Electrical device having two states, on (closed) or off (open). Ideally having zero impedance when closed and infinite impedance when open.


Tantalum Capacitors:
A device for storing a charge of electricity. The dielectric material of these devices will be an oxidized form of tantalum.
A position in a circuit or device at which a connection is normally established or broken.
An electrical resistor with a relatively large negative temperature coefficient of resistance. Thermistors are useful for measuring temperature and gas flow or wind velocity.
Toggle switch:
An electromechanical device used to start or stop current flow along a circuit. Devices in this family are turned on or off through the use of an actuator in the shape of a bat or lever that pivots through an arc at its base.
The variation in the value of a component due to the manufacturing process. It is expressed typically as a percentage.
An electrical component that transfers electrical energy using inductive coupling between two winding circuits.
Devices that transfer, usually through the use of a pair of wound coil wires, electrical energy from one circuit to another.
A semiconductor device used in an electric circuit to regulate current flow to act as a gate, switch, or amplifier for electronic signals.


Universal Serial Bus, an interface for connecting peripherals, including test instruments, to computers.


Variable Capacitor:
Capacitor whose capacitance can be altered by changing the effective area of the plates or the distance between the plates.
Variable Resistors:
Resistor whose resistance can be changed by turning a shaft. Also known as potentiometers
Vibration Sensor:
Devices designed to detect and respond to vibrations of the device.
Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm.
Term used to designate electrical pressure or force that causes current to flow.
Voltage drop:
The difference in voltage from one end of an electrical circuit to the other.
Voltage Regulator:
A device that is placed between the power source and load to provide a constant voltage to the load.
Voltage Spike:
Voltage spikes are rapid, quick duration electrical transients in the electric potential of a circuit.


Unit of electrical power required to do work at the rate of one joule per second. One watt of power is expended when one ampere of direct current flows through a resistance of one ohm. In an AC circuit, true power is the product of effective volts and effective amperes, multiplied by the power factor.
Wave Form:
The representation of a wave in graph-form achieved by plotting wave against time.
A usually pliable metallic strand manufactured in many lengths and diameters. It is sometimes clad and often electrically insulated, used mainly to conduct electricity.
Wire Gauge:
The system used to measure the diameter of wire.




Zener Diode:
Semiconductor diodes in which reverse breakdown voltage current causes the diode to develop a constant voltage. Used as a clamp for voltage regulation.
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