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Preface

The information here is provided as-is and without warranty - check with more established references before making important decisions.

Electricity can be dangerous - even at lower voltages, it silently presents hazards ranging from electric shock to fires and death. If you are unsure about what you are doing, stop and seek professional advice.

Electronics

Concepts

• Direct Current (DC) flows in one direction, either steadily or in pulses.
• Alternating Current (AC) flows in alternating directions across a circuit
• Current refers to the quantity of electrons passing a given point.
  • Unit - Amperes
  • Symbol - I
• Voltage - refers to the electrical pressure or force
  • Unit - Volts
  • Symbol - V
• Resistance - refers to a cause of restriction in the flow of a current
  • Unit - Ohms
  • Symbol - R (or Ω)
• Power - refers to the work performed by a current
  • Unit - Watt
  • Symbol - p
• Potential Difference - the difference in voltage between the two ends of a conductor through which a current flows. Also known as voltage drop.

Ohm's Law

a potential difference of 1 volt will force a current of 1 ampere through a resistance of 1 ohm, or: V = I x R or I = V / R or R = V / I

Ohm's law also is used to calculate power where P = I x V (or I^2 x R)

Abbreviations and Units

Metric Prefixes for SI Units

P (PETA-) = x 1,000,000,000,000,000 (or 10^-15)

T (TERA-) = x 1,000,000,000,000 (or 10^-12)

G (GIGA-) = x 1,000,000,000 (or 10^-9)

M (MEG-) = x 1,000,000 (or 10⁶

K (KILO-) = × 1,000 (or 10³

h (HECTO-) = x 100 (or 10²)

d (DECI-) = x 1.0 (or 10^-1)

c (CENTI-) = x 0.01 (or 10^-2)

m (MILLI-) = x 0.001 (or /1000 or 10^-3)

µ (MICRO-) = x 0.000 001 (or /1000000 or 10^-6) (also mc)

n (NANO-) = x 0.000 000 001 (or /1000000000 or 10^-9)

p (PICO-) = x 0.000 000 000 001 (or /10000000000 or 10^-12)

f (FEMTO-) = x 0.000 000 000 000 001 (or /10000000000000 or 10^-15)

Resistors

A resistor is one of the most common and fundamental passive electronic components, whose primary function is to impede the flow of electric current. It introduces electrical resistance into a circuit. This resistance is a measure of the opposition to current flow. Unlike capacitors or inductors, which store energy, a resistor dissipates electrical energy, typically as heat. The unit of measurement for resistance is the Ohm (Ω).

How Resistors Work 🔥

Resistors work based on the principle of electrical resistance. Inside a resistor is a material that is not a great conductor (like carbon, metal film, or a specific alloy wire). As electrons try to flow through this material, they collide with the atoms within it, losing energy in the process. This opposition to the flow of electrons is the resistance. The amount of resistance is determined by the material used, its length, and its cross-sectional area. This relationship is defined by Ohm's Law, which states that the voltage ($V$) across a resistor is directly proportional to the current ($I$) flowing through it, with the constant of proportionality being the resistance ($R$). The formula is expressed as $V = IR$. The energy lost by the electrons is converted into heat.

File:Resistor color code chart.svg

A chart showing the color-coding system used to indicate the resistance value of a resistor.

What Resistors Are Used For 💡

The primary and most frequent use of a resistor is to limit current. For example, an LED (Light Emitting Diode) can be damaged by too much current, so a resistor is placed in series with it to ensure the current stays at a safe level. Another crucial application is in voltage division. By connecting two resistors in series, you can create a specific voltage level that is a fraction of the source voltage, which is essential for providing the correct voltage to different parts of a circuit.

Further Applications

Resistors are also used as pull-up and pull-down resistors in digital logic circuits. These ensure that a digital input pin settles at a known logical state (either high or low) when it's not actively being driven, preventing an unstable, "floating" state. They are also used in timing circuits with capacitors (RC circuits), where the resistance value helps determine the charging and discharging rate of the capacitor. From setting the gain of an amplifier to acting as heating elements, the simplicity and utility of resistors make them an indispensable component in virtually every electronic circuit ever designed.

Calculating resistance

R_t = Total Resistance

Resistors in series

• R_t = R1 + R2 + R3 (etc)

Resistors in parallel (2 resistors)

• R_t = (R1xR2) / (R1+R2)

Resistors in parallel (3 or more resistors)

• R_t = 1 / ((1/R1) + (1/R2) + (1/RN))

Resistors used as a voltage divider

• V_out = V_in x (R2/(R1+R2))

Resistor component identification

Resistor values are most famously identified using a color code, especially on through-hole components. In the common four-band system, the first two bands represent the significant digits, the third band is the multiplier (the power of 10), and the fourth band indicates the tolerance. For example, a resistor with bands of brown (1), black (0), red (2), and gold (±5%) would be 10 x 10², which is 1,000 Ohms (Ω) or 1 kΩ, with a ±5% tolerance. Precision resistors use a five-band system with three significant digit bands. However, modern Surface Mount Device (SMD) resistors are too small for color bands and instead use a numerical code. A three-digit code like "472" translates to 47 x 10², or 4,700 Ω (4.7 kΩ). Just as with inductors, the letter 'R' is used to denote a decimal point, so "5R6" means 5.6 Ω.

Resistor Colour Codes

Colour	Significant Digits (bands 1&2)	Multipliers (band 3)	Tolerence (band 4)
Black	0	1	-
Brown	1	10	±1%
Red	2	100	-
Orange	3	1000 (k)	-
Yellow	4	10000 (x10k)	No
Green	5	100000 (x100k)	colour
Blue	6	1000000 (M)	band
Violet	7	10000000 (x10M)	±20%
Gray	8	100000000 (x100M)	-
White	9	-	-
Gold	-	-	±5%
Silver	-	-	±10%

Example: a component with Yellow, Violet, Orange and Silver bands could be a 47k resistor with 10% tolerance.

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Capacitors

A capacitor is a fundamental electronic component that stores electrical energy in an electric field. Think of it like a small, rechargeable battery that can charge and discharge very quickly. At its most basic, a capacitor consists of two conductive plates, typically made of metal, separated by an insulating material called a dielectric. This dielectric can be made of various materials, including ceramic, plastic, or even air. The ability of a capacitor to store charge is known as its capacitance, which is measured in units called Farads (F).

How Capacitors Work 🔋

Capacitors work by accumulating charge on their conductive plates. When a voltage source, like a battery, is connected across the capacitor, an electric field is created across the dielectric. This causes positive charge to build up on one plate and negative charge to build up on the other. The dielectric prevents the charge from flowing directly between the plates, so the energy remains stored in the electric field. This process is called charging. When the capacitor is connected to a circuit, it releases this stored energy in a rapid burst, a process known as discharging. The amount of charge it can store depends on its capacitance and the voltage applied.

File:Capacitor schematic with details.svg

A basic diagram showing a parallel-plate capacitor connected in a circuit.

What Capacitors Are Used For 💡

Capacitors are essential in countless electronic devices due to their ability to store and release energy quickly. One of their most common uses is in filtering. In power supplies, they smooth out fluctuations in voltage to provide a steady, clean power source for sensitive electronics. They are also crucial in timing circuits. By controlling how quickly a capacitor charges or discharges, engineers can create precise time delays, which are used in everything from blinking lights to computer clocks.

Further Applications

Another key application is in signal coupling and decoupling. In audio amplifiers, for instance, they block direct current (DC) while allowing alternating current (AC) signals (like the sound waveform) to pass through, ensuring different stages of the circuit don't interfere with each other's DC voltage levels. In camera flashes, a large capacitor is charged over a few seconds and then rapidly discharged to produce a bright burst of light. From radios and computers to mobile phones and electric vehicles, capacitors are a cornerstone of modern electronics, performing a wide range of critical functions.

Calculating Capacitance

Capacitance

• Ct = Total Capacitance

Capacitors in parallel

• Ct = C1 + C2 + C3 (etc)

Capacitors in series (2 capacitors)

• Ct = (C1 x C2) / (C1 + C2)

Capacitors in series (3 or more capacitors)

• Ct = 1 / ((1/C1) + (1/C2) + (1/CN))

Capacitors used as a voltage divider

• Vout = Vin x (C1 / (C1 + C2))

Capacitor component identification

Capacitor identification numbers are typically printed on the component's body to indicate its capacitance, tolerance, and voltage rating. The most common system, especially for smaller ceramic, film, and tantalum capacitors, is a three-digit code. In this code, the first two digits represent the significant figures of the value, and the third digit is a multiplier, indicating the power of 10. This value is almost always in picofarads (pF). For example, a capacitor marked "104" means 10 followed by 4 zeros, which is 100,000 pF. This value is more commonly expressed as 100 nanofarads (nF) or 0.1 microfarads (µF). This number is often followed by a letter that signifies the tolerance (e.g., J = ±5%, K = ±10%, M = ±20%) and a number indicating the maximum working voltage (e.g., 50V). Larger capacitors, such as electrolytic types, usually have enough space to have their full value, unit, and voltage printed directly on them, for example, "470µF 25V".

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Inductors

An inductor is a fundamental passive electronic component that stores energy in a magnetic field when electric current flows through it. Often called a coil, choke, or reactor, an inductor is typically a coil of insulated wire wound around a core. The core material can be air or a magnetic material like iron or ferrite. The ability of an inductor to store energy in a magnetic field is called inductance, and its unit of measurement is the Henry (H).

How Inductors Work 🔋

Inductors operate based on the principles of electromagnetism. When current flows through the coiled wire, it generates a magnetic field around the inductor. If the current changes, the magnetic field also changes, and this change induces a voltage (an electromotive force or EMF) across the coil, according to Faraday's law of induction. This induced voltage opposes the change in the original current, a property known as Lenz's law. In essence, an inductor resists changes in current. When current increases, the inductor tries to hold it back, and when current decreases, it tries to keep it flowing. It stores energy in the magnetic field when current is increasing and releases it when current is decreasing.

File:Inductor with magnetic field lines.svg

An inductor showing the magnetic field generated by the flow of current.

What Inductors Are Used For 💡

Due to their property of resisting changes in current, inductors are vital in many electronic applications. One of their primary uses is in filters. Paired with capacitors, they form LC circuits (or "tank" circuits) that can be used to select or block specific frequencies. This is fundamental to radio tuners and signal processing, allowing you to tune into a specific station while rejecting others. They are also essential in power supplies to smooth out the flow of direct current (DC) and filter out unwanted alternating current (AC) noise.

Calculating Inductance

Inductance

• Lt = Total Inductance

Inductors in series

• Lt = L1 + L2 + L3 (etc)

Inductors in parallel (2 inductors)

• Lt = (L1 x L2) / (L1 + L2)

Inductors in parallel (3 or more inductors)

• Lt = 1 / ((1/L1) + (1/L2) + (1/LN))

Inductors used as a current divider

• Iout = Iin x (L1 / (L1 + L2))

Further Applications

Inductors are also key components in power conversion. In devices like buck or boost converters (found in phone chargers and laptops), inductors are used to efficiently step voltages up or down. Their ability to store and release energy allows for the regulation of voltage and current. Furthermore, inductors are used as sensors to detect magnetic fields or the proximity of metallic objects. From the transformers that power our homes to the wireless charging pads for our phones and even the ignition systems in cars, inductors play a crucial role in managing and manipulating electrical energy across a vast range of technologies.

Inductor component identification

Inductor component identification numbers often follow a system similar to capacitors, but with one crucial difference: the base unit is the microhenry (µH). For many smaller inductors, a three-digit code is used where the first two digits are the significant figures and the third is the power-of-10 multiplier. For instance, an inductor marked "101" is 10 x 10¹, which equals 100 µH. A key feature of this system is the use of the letter 'R' to indicate a decimal point. So, an inductor marked "2R2" has a value of 2.2 µH, and one marked "R15" would be 0.15 µH. This code is typically followed by a letter indicating the tolerance, such as K for ±10% or M for ±20%. Just like with other components, larger inductors and chokes often have sufficient space to have their full value, including the unit (e.g., 10mH for 10 millihenries), printed directly on their casing. Some older through-hole inductors may also use a color-coding system similar to resistors.

Active Components

Semiconductors

Diodes

A diode is a fundamental semiconductor device that essentially acts as a one-way street for electrical current. It allows current to flow easily in one direction, known as the forward bias direction, while severely restricting its flow in the opposite direction, known as the reverse bias direction. This property is achieved by joining P-type and N-type semiconductor materials to form a P-N junction.

Diodes are crucial for a wide range of applications, most notably for converting alternating current (AC) to direct current (DC) in a process called rectification.

Specialised types include Light Emitting Diodes (LEDs), which produce light, and Zener diodes, used for voltage regulation.

Further reading: Diode on Wikipedia

Transistors

A transistor is a semiconductor device that serves as the fundamental building block of modern electronics. Its primary functions are to act as either an amplifier, where it takes a small input signal and produces a larger output signal, or as an electronic switch, turning a current on or off.

The two main families are Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs).

By controlling the flow of a large current with a tiny one, transistors enable everything from simple circuits to complex computations, forming the basis of all microchips, computer memory, and processors.

Further reading: Transistor on Wikipedia

Integrated Circuits (ICs)

An Integrated Circuit (IC), often called a microchip or chip, is a miniaturised electronic circuit consisting of thousands or even billions of electronic components, primarily transistors, diodes, resistors, and capacitors, all fabricated on a single, tiny piece of semiconductor material, usually silicon.

By integrating all these components onto one chip, ICs can perform complex functions at incredible speeds with very low power consumption.

They are the brains behind nearly all modern electronic devices, from simple digital watches and calculators to powerful computers, smartphones, and servers.

Further reading: Integrated Circuits on Wikipedia

Microcontrollers

A microcontroller (often abbreviated as MCU) is essentially a small, self-contained computer on a single integrated circuit.

Unlike a microprocessor (like the CPU in a laptop) which requires external memory and peripherals to function, a microcontroller integrates a processor, memory (both RAM for temporary data and Flash or ROM for storing programs), and various input/output (I/O) peripherals onto one chip. These peripherals allow it to interact directly with the physical world, enabling it to read sensors, control motors, light up LEDs, and communicate with other devices. Designed for specific tasks, microcontrollers are the "hidden" brains in countless everyday items, from microwave ovens and TV remotes to cars and IoT devices, where they execute a dedicated program to manage the device's functions.

Further reading: Microcontrollers on Wikipedia

Optoelectronics

Optoelectronics (often shortened to "opto") is a branch of electronics that deals with devices that source, detect, and control light.

These components convert electrical signals into light or light into electrical signals. Key examples include Light Emitting Diodes (LEDs), which emit light when current passes through them, and photodetectors (like photodiodes or phototransistors), which generate a current when exposed to light.

Another important device is an optocoupler (or opto-isolator), which combines an LED and a photodetector in one package to transmit a signal between two electrically isolated circuits using a beam of light, providing safety and noise reduction.

Further reading: Optoelectronics on Wikipedia

Power

Batteries

A battery is a self-contained electrochemical device that converts stored chemical energy into electrical energy. It consists of one or more cells, each with three main components: a negative electrode (the anode), a positive electrode (the cathode), and a chemical medium called an electrolyte that separates them.

When a circuit is connected, a chemical reaction begins, causing electrons to flow from the anode, through the external circuit to power a device, and then to the cathode, creating a direct current (DC).

Batteries are broadly classified into two types: primary (single-use), like standard AA or AAA alkaline cells, which are discarded once depleted, and secondary (rechargeable), such as the lithium-ion batteries in smartphones and electric cars, which can have their chemical reactions reversed by applying an external power source.

Further reading: Electric Battery on Wikipedia

Electrical

Pages pertaining to house and automotive electrical systems