Electronics components are fundamental building blocks in various professional fields, enabling the design and operation of devices that support modern workplaces across Kenya. From medical equipment at county referral hospitals to security systems in banks and automation in agricultural cooperatives, understanding electronic components is essential for troubleshooting, maintenance, and innovation. This chapter introduces key electronic components and focuses on passive components, providing knowledge applicable to all sectors where electronics are integrated into daily operations.

6.1 Introduction to Electronic Components

Electronics is the branch of electrical engineering that controls the flow of electrons, usually at low voltages and currents, to process signals and control power. Modern welding equipment depends on it: inverter welding machines, wire-feed controls, arc-start circuits, digital displays and protection circuits are all built from electronic components. A welding technologist who understands these components can read a machine's circuit diagram, identify a failed part and test it safely.

Example: the workshop technician at a steel fabrication firm in Ruaraka traces a dead inverter welder to a failed rectifier diode on its main board by following the schematic in the service manual.

6.1.1 Overview of electronics: What are electronic components?

Electronic components are the basic discrete devices that are connected together, usually on a printed circuit board (PCB), to make an electronic circuit. Each component has terminals (leads or pads) and a defined electrical behaviour: it may resist current, store energy, allow current in one direction only, switch, amplify or convert energy. Components are combined into circuits such as power supplies, amplifiers, timers and controllers, and circuits are combined into equipment.

• Discrete components: single devices such as a resistor, capacitor, diode or transistor.
• Integrated circuits (ICs): many components (transistors, resistors, capacitors) made together on one silicon chip.
• Through-hole and surface-mount packages: through-hole parts have leads passing through holes in the PCB; surface-mount devices (SMDs) are soldered onto pads on the board surface.
• Signal and power electronics: signal circuits handle small currents for measurement and control; power circuits (as in welding inverters) switch large currents efficiently.

6.1.2 Classification of components: Passive, active, and electromechanical

Components are classified by how they act on electrical energy.

Passive components

Passive components cannot amplify a signal or control current with another signal; they only resist, store or transfer energy. They need no separate power supply to perform their function. Examples are resistors, capacitors, inductors and transformers.

Active components

Active components can control the flow of current using a small control signal, and so can amplify or switch. They depend on an external power source to work. Examples are transistors, thyristors, operational amplifiers and other integrated circuits. Diodes are semiconductor devices usually grouped with active components because they control the direction of current.

Electromechanical components

Electromechanical components combine electrical and mechanical action: a mechanical movement makes or breaks a circuit, or a current produces a movement. Examples are switches, relays, contactors, connectors, fans, buzzers and small motors.

Other ways of classifying components

• Polarised and non-polarised: diodes and electrolytic capacitors must be connected the right way round; resistors and ceramic capacitors need not be.
• Linear and non-linear: a resistor obeys Ohm's law (linear); a diode does not (non-linear).
• Analogue and digital: analogue devices work with continuously varying signals, digital devices with two levels (0 and 1).

6.1.3 Introduction to circuit symbols and schematic diagrams

A schematic (circuit) diagram shows how components are connected, using standard symbols (BS EN 60617 or IEC 60617) rather than pictures. It shows connections, not the physical layout on the board. Being able to read schematics is essential for fault-finding on welding power sources and control boards.

Common circuit symbols

Reading a schematic

• Signal flow: diagrams are usually drawn with inputs on the left and outputs on the right.
• Supply rails: positive supply at the top and 0 V (ground) at the bottom.
• Junctions: a dot shows a joined connection; crossing lines without a dot are not connected.
• Reference designators: each part is labelled R1, C3, D2, Q1, IC4, and listed in the parts list.
• Block diagrams: a simplified diagram showing each stage as a box (rectifier, inverter, transformer, output) is often read first.

6.1.4 Basic electrical quantities and units (voltage, current, resistance)

All electronic circuits are analysed with a few basic quantities.

Ohm's law and power

V = I × R

P = V × I = I² × R = V² ÷ R

Example: A 470 Ω resistor has 12 V across it. Find the current and the power dissipated.

I = V ÷ R = 12 ÷ 470

I = 0.0255 A (25.5 mA)

P = V × I = 12 × 0.0255

P = 0.306 W, so a resistor rated at least 0.5 W should be used.

Prefixes used in electronics

• Pico (p): × 10⁻¹², used for small capacitors (100 pF).
• Nano (n): × 10⁻⁹, for capacitors (47 nF).
• Micro (µ): × 10⁻⁶, for capacitors and currents (100 µF, 50 µA).
• Milli (m): × 10⁻³, for currents and voltages (20 mA, 500 mV).
• Kilo (k) and mega (M): × 10³ and × 10⁶, for resistances (4.7 kΩ, 1 MΩ).

6.1.5 Understanding datasheets and component specifications

A datasheet is the manufacturer's document giving the ratings, characteristics, pin connections and package dimensions of a component. It is used to choose a component, design with it and find a correct replacement.

Main parts of a datasheet

• Absolute maximum ratings: limits that must never be exceeded, such as maximum voltage, current, power and junction temperature.
• Electrical characteristics: typical, minimum and maximum values under stated test conditions, for example a diode's forward voltage at a given current.
• Pin configuration: a drawing showing which pin is which (for example base, collector and emitter of a transistor).
• Graphs: curves such as voltage against current, or derating of power with temperature.
• Package and mounting information: dimensions, footprint and soldering profile.
• Ordering information: full part numbers and variants.

Key specifications by component

• Resistor: resistance, tolerance (for example ±1%), power rating, temperature coefficient.
• Capacitor: capacitance, working voltage, tolerance, temperature range, equivalent series resistance.
• Diode: maximum reverse voltage, maximum forward current, forward voltage drop, recovery time.
• Transistor: maximum collector-emitter voltage, collector current, power dissipation, gain.

A replacement part should match or exceed the original's ratings and fit the same package and pin layout.

6.1.6 Overview of testing and measurement tools (multimeters, oscilloscopes)

Testing tools let the technician measure quantities and check components without guessing.

Using a multimeter

1. Select the function and range: choose V, A or Ω and a range above the expected value.
2. Connect the leads correctly: black to COM, red to the V/Ω socket (or the A socket for current).
3. Measure voltage in parallel: place the probes across the component.
4. Measure current in series: break the circuit and insert the meter.
5. Measure resistance with power off: isolate the circuit and discharge capacitors first.
6. Read and record: note the value and units, then switch the meter off or to a voltage range.

Using an oscilloscope

An oscilloscope plots voltage (vertical axis) against time (horizontal axis). The technician sets the volts per division and time per division, connects the probe and earth clip, and adjusts the trigger to obtain a steady trace. From the trace, the peak voltage, period (and so frequency, f = 1 ÷ T) and the shape of the waveform can be read.

Handling and storage of components

• Static protection: semiconductor components are damaged by static; use an earthed wrist strap and anti-static mat.
• Dry storage: store components in dry, cool, labelled containers.
• Shelf life: electrolytic capacitors that have been stored for years may need reforming or replacement.
• Identification: keep components in their labelled bags or drawers to avoid using the wrong value.

Chapter Summary

This chapter provides a comprehensive introduction to electronic components, covering their classification into passive, active, and electromechanical types, as well as the interpretation of circuit symbols and schematic diagrams. It explains fundamental electrical quantities such as voltage, current, and resistance, and guides students on how to read datasheets and use testing tools like multimeters and oscilloscopes. The section on passive components explores resistors, capacitors, and inductors, detailing their types, characteristics, and roles in circuits including filtering and timing functions. Semiconductor devices are examined next, focusing on diodes, transistors, and special components like thyristors, highlighting their properties and applications in switching and amplification. Integrated circuits are introduced with distinctions between analog and digital types, emphasizing operational amplifiers, timers, voltage regulators, and digital logic devices. The chapter concludes by discussing electromechanical components such as relays and transformers, various display technologies, and essential circuit design practices including breadboarding and PCB layout. Practical aspects of testing, troubleshooting, and project building are integrated throughout to connect theory with real-world electronics applications.