How to Read Circuit Boards and Identify Components [Solve]

The question "How to read circuit boards" or "How to read schematics" often arises for beginners. Sometimes "What is this component" may also arise. These questions can be solved altogether in this article guiding how to read a circuit board and identify components.

circuit board

How to Read Circuit Boards - Standards for Electronic Symbols

A printed circuit board is a bunch of electronic components interconnected via conductive paths printed on a baseboard.

The electronic components and conductive paths are based on a map, the schematic diagram. This diagram is drawn based on widely-accepted rules and symbols.

The symbols used in schematic diagrams are according to standards that are defined at the National and International level by professional organizations, such as the Institute of Electrical and Electronics Engineers (IEEE), the International Electrotechnical Commission (IEC), and the American National Standards Institute (ANSI).

Following are some of the common standards for electronic symbols.

IEC 60617
ANSI Y32.2-1975
IEEE Std 91/91a

Where to Start Reading Circuit Boards - Power Source

If you have a schematic diagram or a circuit board, the best and easiest way to start analyzing it is from the power source. Every electronic component depends on some sort of power supply. Commonly the designing process of a circuit also begins from there.

The most common type of failure in electronic devices is also power supply failure. Following are the common symbols associated with the power source.

Symbols related to the power source

Direct Current (DC) Supply Symbols	Alternative Current (AC) Supply Symbols

Current Source Symbol	Battery Symbols

Controlled Voltage Source	Controlled Current Source

Solar Cell Symbol	Ground (Earth) Symbols

Fuse	Transformer

The connections within those symbols are shown with lines. And these lines (conductive paths) have joints and crossings. The below symbols represent these.

Trace Junction	Trace Crossing

Reading Schematics - Passive Components

After identifying the power supply, the next most common electronic components are the passive components. The name "passive component" is used for electronic components that cannot inject power or amplify the power in a circuit.

Passive components can only absorb, dissipate, or store energy. These components do not need a set level of voltage (energy) to perform a task.

Common component types that fall into this category are resistors, capacitors, inductors, and transformers.

Resistors

Resister is a component that acts as a barrier to the current flow. It dissipates energy as heat and creates a voltage drop in the circuit. The resistance value (R) is given in terms of "Ohms", and the voltage drop can be calculated from Ohm's Law Equation.

V = IR

(V = voltage, I = current, and R = resistance)

Resistor	Variable Resistor (Rheostat)

Potentiometer	Termister or Varistor

Capacitors

Capacitors are components that store energy in an electric field. The capacitance value (C) is given in terms of "Farads". The governing primary equation of capacitors is,

(C =capacitance, Q = charge in qoulomb, V = Voltage)

Unpolarized Capacitor	Polarized Capacitor

Variable Capacitor	Trimmer Capacitor

Inductors

Inductors are components that store energy in a magnetic field. Inductance (L) is measured in "Henry". The primary governing equation of Inductors is,

( Φ = magnetic flux linkage, I = Current, L = Inductance)

Air Cored Inductor	Magnetic Core Inductor

Tapped Inductor	Ferrite Bead

Transformers

Transformers are used to step up or step down voltages and currents. Energy is transferred in a transformer via a varying magnetic flux. Primary winding induces this magnetic flux, and there are one or many secondary windings that get induced currents from this core magnetic flux. Voltage and current induced here are proportional to the number of turns in the windings.

The governing primary equations of transformers are,

(Vp = Primary Winding Voltage, Vs = Secondary Winding Voltage, Np = Number of coils turns in the primary winding, Ns = Number of coils turns in the secondary winding, Ip = Primary Winding Current, Is = Secondary Winding Current.)

Transformer	Transformer with tapping

Current Transformer	Voltage Transformer

RLC circuits

These are circuits only composed of passive components. These are common in power transmission systems, audio noise filtering systems, EMI filters, and passive frequency filters.

EMI Filters	Audio Filters

Reading Schematics - Common Active Components

Active components are the heart of modern electronics. They are usually made of semiconductors. To perform tasks these components need a set level of voltage or they supply energy to the circuit.

Voltage sources, current sources, generators, all components made of transistors, and all types of diodes are examples of active components.

Let's see some common symbols of active components.

Transistors

There are tons of transistor types, and each has a unique symbol. Transistor type cannot be determined from its appearance because different types of transistors have the same package type. Transistor type can only be accurately recognized from its model number and symbol. Here we mention some of their most common types.

N-channel junction gate field-effect transistor (JFET)	P-channel junction gate field-effect transistor (JFET)	Metal-oxide-semiconductor field-effect transistor (MOSFET)

Enhancement mode, N-channel MOSFET	Enhancement mode, P-channel MOSFET	NPN bipolar junction transistor (BJT)

PNP bipolar junction transistor (BJT)	NPN Darlington transistor	PNP Darlington transistor

Diodes

Diodes are gates that allow current to flow in one direction only. These are commonly used for rectifying AC currents into DC currents in the power supply. Other types of diodes emit light which is called light-emitting diode (LED) and there are diodes that capture light and convert it into a current which is called photodiode. All diodes are made of semiconductors and have a P-N junction.

Rectifier Diode	Schottky diode	Zener diode

Light Emitting Diode (LED)	Photodiode	Tunnel diode

Varicap diode	Shockley diode	Silicon-controlled rectifier (SCR)

Constant-current diode	Diac	Bridge rectifier

Integrated Circuits (ICs)

Integrated Circuits (IC) consist of from a few transistors to a few billion transistors. In the modern day, they perform all the main tasks of any circuit. They provide logical computational power, storage, switching tasks, and many more. Integrated circuits are easily identifiable by their package and number of pins. These usually have a higher number of pins than any of the above components. The building block of most ICs is the operational amplifier (opamp). Since there are too many variants of ICs, here we look into only the basic IC symbol which is the OP-AMP.

Operational Amplifier (Op-Amp) or Comparator

Reading Schematics - Other Components

Apart from all the above primary components, there are many other key components in circuits that play vital roles. These can be electro-mechanical components such as relays, speakers, solenoids, connectors, and switches.

Or there can be other types of electronic components that do not fall into the above main categories like crystal oscillators, hall-effect sensors, displays, etc.

Crystal Oscillator	Hall-Effect Sensor	Loudspeaker

Microphone	Bulb	Relays

Switches	Motors	Solenoids

From Reading Circuit Boards to PCB EMS Manufacturing

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