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Circuit Board Components: How to Identify Components on a PCB

It's fundamental to understand the basic circuit board components, whether you are just starting your journey into electronics or looking to level up your skills. Each circuit board part plays a unique but complementary role in bringing projects to life, from resistors and capacitors to integrated circuits and sensors.

However, with dozens of components regularly used on even simple boards, navigating the sea of parts can feel overwhelming. This guide aims to break down the essential circuit board components. We'll explain what each PCB component does, how it works, common types you may encounter, and examples of how they are used.

What are the Components of a Printed Circuit Board?

A printed circuit board (PCB) contains several key electronic components that work together to power our electronic devices. Here are some of the most important and common components found on circuit boards (circuit board components list).

Integrated Circuits (ICs)

integrated circuits
Integrated circuits (ICs), also called chips or microchips, are one of the most fundamental building blocks of modern electronics. ICs allow entire circuits to be constructed in a tiny space thanks to miniaturized transistors and other components. ICs can contain thousands of tiny electronic components like transistors, resistors, and capacitors etched onto a small silicon chip.

This level of miniaturization has enabled today's powerful computers, phones, and other devices. ICs come in different packages, from simple through-hole devices to complex surface-mount chips. No matter their size or shape, ICs act as the "brain" of a circuit board, performing complex operations and functions.


Resistors are one of the most basic and commonly used circuit board components. Their essential function is to resist or limit the flow of electrical current in a circuit. Resistors are crucial for controlling current, dividing voltages, and providing terminating impedances in electronic circuits. They are available in a variety of resistance values and tolerance levels.

On circuit boards, resistors are typically small cylindrical or rectangular components with color-coded bands indicating their resistance. Their simple yet critical role makes resistors one of the most plentiful parts found on most PCBs.



Capacitors are the second most widely used circuit board component after resistors. Their function is to store electrical charge and smooth voltage in a circuit temporarily. Capacitors utilize two conductive plates separated by an insulating material known as a dielectric. Different types of dielectric materials provide various capacitance values.

Capacitors come in many shapes and sizes but are mainly identified by their capacitance rating. Common types included on circuit boards include ceramic disc capacitors, tantalum capacitors, and electrolytic capacitors. Capacitors play an important role in regulating voltage levels, decoupling noise, and filtering signals - key functions necessary for proper circuit operation.



Inductors are another important component found on circuit boards. Similar to capacitors, inductors store energy, but instead of electric charge, they store energy as a magnetic field. Inductors are coils of wire wrapped around a core, often a ferromagnetic or ferrite material. As current passes through the coil, it creates a magnetic field proportional to the current and number of turns in the coil.

Inductors have the property of resisting changes in current flow, making them integral to functions like filtering noise and smoothing fluctuations in alternating current circuits. Common inductors seen on PCBs include wire wound, multilayer, and shielded inductive components available in various inductance values.



Connectors are essential interface components that allow boards to connect with off-board circuitry and other devices. Common connector types used in electronics include pin headers, wire-to-board terminals, ribbon cables, board-to-board headers, and external connectors like USB, HDMI, and modular jacks.

● Pin headers are basic inline connectors that link boards to things like breadboards during prototyping
● Terminal blocks terminate wires from external devices
● Ribbon cables and board-to-board headers interconnect multiple circuit boards internally or within larger devices
● External connectors provide industry-standardized interfaces for common I/O functions.

Connectors must be rugged enough to make and break connections during assembly/service life cycles. Their pin-out configurations comply with interface standards to enable integration into systems.



Transformers are circuit board components used to transfer electrical energy from one circuit to another through electromagnetic induction. They are composed of two or more coils of wire wrapped around a shared core. Varying the number of coil windings changes the voltage transferred according to the transformer equation.

Common transformer uses include power supplies where step-down transformers lower hazardous voltages for safe consumption or step-up transformers increase voltage for transmission applications. 

Communication devices also employ transformers to match impedances across transmission lines.

Signal isolators use transformers to isolate sensitive circuits from noise-prone environments electrically. On PCB boards, transformers appear as discrete through-hole or surface-mount components dedicated to AC voltage conversion applications.

Crystal Oscillators

crystal oscillators

Crystal oscillators are timing elements found on circuit boards. They contain a piece of piezoelectric material, usually quartz crystal, that physically oscillates at an exact frequency when an electric current is applied. This oscillation produces a periodic electronic signal that serves as a reference clock source.

Onboard clocks are crucial as modern circuits rely on precise timing to function correctly. The crystal oscillates reliably to keep microcontrollers synchronized and ensure processes occur at the right intervals. Their stability and small size make crystals well-suited for applications requiring accuracy, like computers and phones. Crystals typically oscillate between 1MHz and 100MHz, falling within frequency ranges needed by different chips.



Transistors are fundamental electronic components that act as switches or amplifiers. The most widely used type is the bipolar junction transistor (BJT), which has three terminals: base, collector, and emitter. 

When a small current is applied to the base terminal, it allows a much larger current to flow between the collector and emitter terminals. This switching action amplifies electrical signals and regulates current, enabling critical functions.

BJTs are found in units ranging from simple radios to advanced processors. Transistors form the basis of digital electronics and computers as they can be arranged to perform logical operations. Their reliable switching at low power consumption is why transistors became the fundamental building block of all modern electronic devices.



Diodes are one-way electronic valves that allow current to flow in only one direction. The most common type is the light-emitting diode (LED), which emits light when current flows through it in the forward bias direction from the anode to the cathode. On circuit boards, diodes protect components by blocking current flowing in the wrong direction, preventing damage. LEDs are also widely used as indicator lights.

Other diode types enable functions like current rectification. For example, diode rectifiers convert alternating current from power sources to the direct current used within circuitry. Their direction-specific conduction allows diodes to control signal and power flow and play essential roles in signaling and power regulation functions, making diodes ubiquitous components in all modern electronic devices.

Silicon-Controlled Rectifiers (SCRs)

silicon-controlled rectifiers

SCRs are semiconductor devices similar to diodes and transistors. Also known as thyristors, they have four alternating layers of semiconductor material that allow current flow in only one direction when a trigger signal is supplied to the gate terminal. This triggers the SCR into conducting mode.

On circuit boards, SCRs are commonly used components as electrically controlled switches in applications like light dimmers, where they regulate current flow. Their conducting once-triggered property makes SCRs well-suited to switching higher currents with only low-power control signals.



Fuses are safety devices on circuit boards to protect other circuit board components and wiring from overcurrent damage. They contain a fine wire or strip of metal that melts when too much current passes through. This interrupts the circuit to prevent components from burning out.

Fuses come in various amperage ratings and physical forms like glass cylinders or electronic surface mount. Their inclusion is vital as it limits damage from short circuits or power surges to only the fuse, avoiding cascading failures across the entire board.



Potentiometers are variable resistors whose resistance can be changed by an external mechanical device like a dial or slider. On circuit boards, common implementations are single-turn potentiometers adjusted through a knob or linear potentiometers with slider bars. Their versatility enables real-time adjustment of circuit parameters like volume controls.

During production, multi-turn potentiometers allow the calibration of circuits. Potentiometers see widespread use as any circuit requiring a continuously adjustable input value can make use of a potentiometer's varied resistance.



Relays are electrically operated switches supplemented with coils of wire that create magnetic fields. On circuit boards, relays are parts that allow low-power input signals to control circuits handling higher currents or voltages safely. When engaged, the magnetic field pulls a set of contacts closed to complete a separate circuit.

Relays thus integrate mechanical components into electronic solutions. Common uses include controlling heavy loads beyond component ratings and isolation of high and low-voltage sections. As the coil and switch contacts are electrically isolated, relays provide more robust switching than solid-state components.

How to Classify the Circuit Board Components

With the multitude of parts present on any given PCB, it is important to understand how they are classified to identify components and understand their purpose. In general, the circuit board components are divided into mechanical and electrical. Each classification works differently and is specific to perform critical functions in PCB design and manufacturing. Let's take a closer look at each.

various circuit board components

Mechanical Components

Mechanical components play an integral role in circuit boards, providing the physical structure needed to interconnect electronic parts reliably. These mechanical elements are just as important as the electrical components themselves. Without robust mechanical design, it would not be possible to assemble all the necessary pieces in a compact yet durable package. Some examples of mechanical components on circuit boards include:

● Connectors
● Standoffs
● Screws and nuts
● Shielding
● Traces

Circuit boards require various mechanical parts to hold electrical components in exact positions, connect the board to other devices, protect sensitive components from damage, and provide insulation. These mechanisms give the rigid physical framework circuit boards need to maintain precise alignments and connections.

They fasten everything together securely while separating elements as required to prevent electrical issues. The mechanical design ensures the system can withstand transportation and handling and operate correctly in end-use environments. This makes the computational function of the board possible. Comprehensive mechanical integration is, therefore, key to the production of high-quality circuit boards.

Electrical Components

The electrical components of circuit boards are the parts that handle the flow of electricity through the board. They allow current to pass between different areas of the circuit. Electrical circuit board components differ from mechanical components in that mechanical parts are used for physical structure and connections rather than electrical functions.

Mechanical components provide support and connection points for attaching electrical parts but do not regulate or control electricity flowing through the circuit. Electrical components are what make the circuit functional by controlling or directing current flow.

There are two main types - passive and active components. Let's take a closer look at both of them.

Passive Electrical Components on Circuit Boards

passive circuit board components

Passive electrical components are an essential part of any electronic circuit. They are defined as components that do not require a power source to function, unlike active components that do require a power source. Passive components alter the flow of electric current through a circuit without using any power.

Passive components work simply by imposing resistance, capacitance or inductance into an electric circuit. Resistance reduces or limits current flow, while capacitance stores electric charge between conductors separated by an insulator. Inductance is the ability of a conductor to oppose a change in electric current flow. These intrinsic properties allow passive components to control voltage, current, and power levels within a circuit.

Because of their simple functioning without an external power source, passive components are classified differently than active components. Some common types of passive components include:

● Resistors
● Capacitors
● Inductors
● Transformers
● Diodes
● Connectors

They provide simple but crucial roles in shaping electric signals and directing power in both analog and digital circuits.

Active PCB Components 

active circuit board components

Active components are a crucial part of any electronic printed circuit board (PCB) as they are able to generate, control, modify, and strengthen electrical signals. Unlike passive components that can only attenuate, store, or release energy, active circuit board components require external power to function and are capable of controlling or amplifying signals.

Active components serve as the "brains" of a PCB as they can process inputs and use internal mechanisms to generate outputs. They contain semiconductors like transistors and integrated circuits that can both control electric current and be controlled by varying voltage inputs. The active flow of electric charges within their semiconductor material allows for functions like switching, oscillation, signal amplification, and data processing.

Some examples of common active components found on PCB boards include:

● Transistors
● Integrated circuits/chips
● Microprocessors
● Optocouplers
● Diodes
● Op-amps
● Thyristors

Active components play a critical role in electronics by controlling signal levels, timing, switching power on/off, processing data, and performing other important logic functions essential for PCB operation.

How to Identify the Components on a Circuit Board

As we have already seen, printed circuit boards contain a variety of electrical components that perform different functions within electronic devices and systems. However, identifying individual parts can sometimes be challenging for those unfamiliar with circuit board design.

Here are some helpful tips for determining what each part is and what it does.

Determine the Board's Purpose

The first step is to examine the entire board to determine its overall function. Look for any part numbers, model names, or descriptive text printed on the board itself that can provide context. Is it a main system board, add-on module, or dedicated controller?

Boards intended for computers, industrial machines, and medical equipment often have standardized layouts and components for their functions. Taking note of a board's purpose will help narrow down what to expect from it.

Inspect Passive Components in Detail

Passive components like resistors, capacitors, and inductors are good places to start identification due to their consistent designs. Resistors may have color-coded bands indicating resistance value. Look closely, as some have all-numeric printing instead.

Capacitors are marked with the letter C followed by capacitance rating in farads or a coded system of numbers and letters. Inductors resemble small coils labeled L. Take time to examine passive parts' physical features, labels, and relative locations for clues.

Carefully Evaluate Integrated Circuits

Integrated circuits (ICs) are complex active devices that condense multiple transistors and other components onto a single silicon chip. They often have part numbers or manufacturer markings printed right on the surface that can be researched.

Depending on age, an IC may simply have a functional label like 7400 instead of a detailed number. ICs' varying shapes and pin configurations also provide clues. Give ICs extra scrutiny, as correct identification reveals critical roles

Identify Other Discrete Circuit Board Components

Transformers, relays, connectors, and diodes are generally labeled with standardized initials like T, K, J, or D. Transformers resemble small multiply-wound coils. In contrast, relays look similar to an electrically operated switch.

Diodes may have stripe patterns on cylindrical packages indicating polarity. Batteries are usually stamped BT. Discrete parts don't hold as many internal details as ICs, but understanding common symbols aids recognition.

Consult Inline Reference Designators

Some circuit boards include alphanumeric reference designators directly on traces near each part for reference. Though formats vary, these abbreviations paired with placement point to a circuit board component's identity and purpose within the circuit. Take advantage of clearly marked references when deciphering obscure components' functions. 

The abbreviations listed in the table below are some of the most commonly used designators and their standard abbreviations for different electronic components of circuit boards.

Designator Components


BR Bridge Rectifier
BT Battery
C Capacitor
CB Circuit Breaker
CN Capacitor Network
DC Directional Coupler
D Diode
F Fuse
G Oscillator
IC Integrated Circuit
J Jumper or Jack
K Relay or Contactor
L Inductor
LED Light-emitting Diode
LS Loudspeaker
MOV Metal Oxide Varistor
P Plug
POT Potentiometer
PS Power Supply
Q Transistor
R Resistor
S or SW Switch
TB Terminal Block
TC Thermocouple
TP Test Point
TR Transducer
T Transformer
U Integrated Circuit
VR Variable Resistor
X Transducer
XTAL Crystal
Z Zener Diode
ZD Zener Diode

Research Unknown Components Thoroughly

If a circuit board component remains unidentified after thoroughly examining physical properties, labels, and reference designators, turn to other resources like manuals, diagrams, or online component databases with searchable part numbers before making assumptions. 

Methodical inspection cross-referenced with documentation maximizes recognition of even antiquated PCB elements. Professional-grade schematics may also be required in complex cases.

How are Circuit Board Components Connected in a PCB?

how are circuit board components connected in a pcb

Components are connected on a printed circuit board through a network of pathways called traces. Traces are thin copper strips laminated between layers of a non-conductive substrate like fiberglass. 

Components like integrated circuits, resistors, and capacitors have miniature metal pads on their bodies where wires can be soldered, or components can be inserted directly into holes in the PCB called vias.

Traces carry signals and current throughout the PCB, linking the pins or pads of one component to another to transfer data and power around the circuit. Components can be surface mounted directly onto the PCB traces or inserted vertically into through-hole plated vias that electrically connect the top and bottom layers of the board. Decals known as solder masks are screened over the board to protect the traces and provide isolation between connections.

Holes through the board called plated-through holes allow traces on internal layers of the PCB to connect with the top and bottom exterior layers, vastly increasing the number of possible circuit routes and interconnections. Together, the traces and plated holes form a dense wiring matrix that propagates signals and controls current flow between silicon chips and other pieces in an electronic device.


At their core, circuit boards are deceptively simple—they're just connections between electronic components. However, as we've explored, countless components can go on a circuit board, each serving a unique and vital role.

Mastering the basics of circuit board components like resistors, capacitors, transistors, and integrated circuits is an essential first step for anyone interested in electronics or circuit design. With continued learning and hands-on practice, you'll understand how circuit board parts interact and the possibilities they enable when combined in different configurations on a PCB.


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