PCB (printed circuit board) Parts and Components Identification


PCB (printed circuit board) Parts and Components Identification

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Printed circuit boards are used in all but the simplest electronic products. They are also used in some electrical products, such as passive switch boxes.


Resisters limit the flow of current through a circuit. These small, horizontal cylinders often bear four or five colored stripes that help identify their resistance and tolerance. Larger resistors may have this information written on them as well.

Their schematic systems can also have this information printed in words as well. In either case, PCBs use R to note resistors.

Transistors are a particular type of switch. You can identify them by their three terminals and their “D” shape. Circuit boards often use Q to indicate transistor locations.

Transistor diagrams are circles with three leads. Inside the circle, one point goes directly to a bar, while the other leads branch off diagonally from the bar with one of them containing an arrow.

Relays are electronic switches. Powered relays are open while disconnected relays are closed. These components typically have plastic shells with their specification written on them. Most boards use “K” to label relays. 

Transformers are normally pretty easy to identify by sight, and many have their specs printed on them. They are typically marked with an “T” on a circuit board.

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A switch is a component which controls the open-ness or closed-ness of an electric circuit. They allow control over current flow in a circuit (without having to actually get in there and manually cut or splice the wires). Switches are critical components in any circuit which requires user interaction or control.

These variable resistors are usually marked in ohms using three digits. The first two digits are the significant figures with the third proving the power of 10 multipliers.

Potentiometers also have a letter code to indicate the resistance change, and a VR for variable resistor marked on them somewhere.

These complete circuits-on-a-chip will take some effort to identify correctly, as several different types of ICs can come in the same package. Marked as U or IC on most circuit boards, you often need to look up the device’s datasheet to find the information.

Datasheets offer a schematic of their devices and are typically found online. Circuit diagrams use rectangular blocks to represent these components.

Essentially loops of wire, inductors are often difficult to identify. You can find them either as a raw wired coil or color coded. In either case, you should test the components before using them. Fortunately, PCBs use an L to indicate an inductor.

In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby interrupting the current. It is a sacrificial device; once a fuse has operated it is an open circuit, and it must be replaced or rewired, depending on type.

Diodes one-way electrical components with a band that indicated the current direction. You can find their specs on their shells. You may also come across LEDs and Zener diodes as well.

Diagrams use an arrowhead and a bar to indicate diodes while circuit boards use D or CR. The arrow points in the direction of the current.

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Marked on boards with an X or Y, these natural clocks keep our electronic devices working smoothly and on time. The unique appearance of a crystal oscillator makes these components the easiest to identify. They also have their specification written on them.

Capacitors store electric charge. These components come as small disk-shaped gumdrops or large cylinders. In either case, the information is printed directly onto them. PCBs, use C to make capacitors.

A Bridge rectifier is an Alternating Current (AC) to Direct Current (DC) converter that rectifies mains AC input to DC output. Bridge Rectifiers are widely used in power supplies that provide necessary DC voltage for the electronic components or devices. They can be constructed with four or more diodes or any other controlled solid state switches.
Depending on the load current requirements, a proper bridge rectifier is selected. Components’ ratings and specifications, breakdown voltage, temperature ranges, transient current rating, forward current rating, mounting requirements and other considerations are taken into account while selecting a rectifier power supply for an appropriate electronic circuit’s application.

A LED, or light emitting diode, is a component that can give off light. You can find them in single and multi-color and low and high-power varieties. Low-power, single color LEDs are the most common. They often come in their respective colors, but not always.

They will only have two terminals, a cathode, and an anode. Multi-color ones have more than one color and a set of terminals for each color. High-power LED has a large metal casing to dissipate the extra heat. LEDs use the diode symbol on diagrams.