Electronics glossary: plain-English definitions

66 electronics terms, each explained in one or two simple sentences, with a link to the short lesson that shows it. Written for total beginners.

5

555 timer

A classic 8-pin timer chip. With two resistors and a capacitor it blinks an LED or makes a tone with no code at all. Lesson: The 555 timer: one chip that blinks →

A

AC (alternating current) AC

Current that reverses direction many times a second. Mains power is AC: 230 V at 50 Hz in India, the UK and Europe, and 120 V at 60 Hz in the USA and Canada. Lesson: AC vs DC →

ADC (analog-to-digital converter) ADC

The circuit that turns a voltage into a number. On an Arduino Uno, analogRead() gives 0–1023 for 0–5 V (10 bits). Lesson: Speed knob: potentiometer + analogRead →

Arduino

An open-source family of microcontroller boards plus a simple programming tool. The Arduino Uno uses an ATmega328P running at 16 MHz and 5 V. Lesson: Inside an Arduino Uno →

B

Bit shift 1 << n

A C operator that moves bits left or right. 1 << 5 produces a value with only bit 5 set (0b00100000 = 32), used as a mask to control one pin. Lesson: Embedded C Part 8: the bit shift trick — what does 1 << 5… →

Bluetooth

A short-range 2.4 GHz radio link for earbuds, watches and sensors. Bluetooth Low Energy sleeps most of the time, so it uses very little power. Lesson: Explained Simply #16: how do wireless earbuds talk to your… →

Breadboard

A reusable board for building circuits without soldering. Each short row of five holes is joined inside, and the long side rails carry plus and minus. Lesson: Workbench Skills Part 8: the breadboard — which holes are… →

Brushless motor (BLDC) BLDC

A motor with no brushes: an electronic speed controller switches its three coils in turn. It is efficient and long-lasting, and is used in drones, fans and e-bikes. Lesson: Motors & Drivers Part 6: Brushless motors — how drones… →

C

Capacitor C

Two metal plates with an insulator between them that store electric charge. It is measured in farads (F), smooths voltage, sets timing and blocks DC while letting AC through. Lesson: How a capacitor stores energy →

Continuity test

A multimeter mode that beeps when there is an unbroken path between the two probes. It is used, with the power off, to find broken wires and blown fuses. Lesson: Workbench Skills Part 4: Continuity beep — find a broken… →

Current A

The flow of electric charge through a wire, measured in amperes (amps, A). 1 A is about 6.24 billion billion electrons passing a point every second.

D

DC (direct current) DC

Current that flows in one direction only, as from a battery, a USB port or a solar panel. Lesson: AC vs DC →

Decibel dB

A logarithmic way to compare two power levels. +3 dB is about double the power and +10 dB is ten times the power. Lesson: Decibels (dB): why +3 dB = double →

Decoupling capacitor

A small capacitor (often 100 nF) placed right next to a chip's power pin. It supplies short bursts of current and keeps the chip's supply voltage steady. Lesson: Capacitor Series Part 6: Decoupling caps — the tiny… →

Diode D

A one-way valve for current: it conducts from anode to cathode and blocks the other way. A silicon diode drops about 0.7 V when conducting. Lesson: The DIODE: the one-way valve that turns AC into DC →

E

Earthing (grounding)

A low-resistance wire from an appliance's metal body to the ground. If a live wire touches the body, the fault current flows to earth and trips the protection instead of shocking you. Lesson: Earthing: how an earth pit works →

Efficiency η

The share of input power that comes out as useful output: output ÷ input × 100 %. The rest becomes heat. Lesson: Maths for Electronics L14: Efficiency — where does the… →

Embedded C

Plain C that runs directly on a microcontroller with no operating system, controlling pins through hardware registers. Lesson: What is Embedded C? →

ESC (electronic speed controller) ESC

The board that drives a brushless motor. Six MOSFETs feed the three coils a pair at a time, at a speed set by a throttle signal. Lesson: Motors & Drivers Part 8: the ESC — the brain between the… →

ESP32

A low-cost microcontroller with Wi-Fi and Bluetooth built in. Its pins work at 3.3 V, not 5 V. Lesson: ESP32: Wi-Fi + Bluetooth on one chip →

F

Flash memory

Memory that keeps data with the power off by trapping electrons in tiny insulated cells. It is used in phones, SSDs, USB sticks and microcontrollers. Lesson: Explained Simply #5: How does your phone remember things… →

Footprint

The pattern of copper pads on a PCB that one part is soldered to. A schematic symbol shows what a part does; its footprint shows its real shape and size. Lesson: PCB Design with KiCad Part 6: symbol vs footprint — one… →

Frequency Hz

How many full cycles happen each second, measured in hertz (Hz). Frequency = 1 ÷ period, so 50 Hz mains has a 20 ms cycle. Lesson: Frequency: f = 1 ÷ T →

G

GPU

A processor with thousands of small cores that work on many pixels at once, so it draws games and video far faster than a CPU. Lesson: Chips Part 6: What is a GPU? Thousands of small cores →

I

Inductor L

A coil of wire that stores energy in a magnetic field and resists changes in current. It is measured in henries (H). Lesson: The inductor: the coil that fights change →

Inverter

A device that turns DC from a battery or solar panels into AC for home appliances. Lesson: Inverter backup: how long will your battery last? →

IoT (Internet of Things) IoT

Everyday objects with a small chip, a sensor and a network connection that send data to the internet and take commands from an app. Lesson: What is the Internet of Things (IoT)? (you asked) →

K

KiCad

A free, open-source program for designing PCBs. It includes a schematic editor, a PCB editor and a 3D viewer. Lesson: PCB Design with KiCad Part 2: Why KiCad? →

Kilowatt-hour (kWh) kWh

The unit of energy on an electricity bill: 1 kWh = 1,000 W used for 1 hour. A 100 W device running for 10 hours uses 1 kWh. Lesson: What is 1 unit of electricity? (kWh) →

L

LDR (light-dependent resistor) LDR

A resistor whose resistance falls as light gets brighter: about 1 kΩ in bright light and up to about 1 MΩ in the dark. Lesson: Sensors Part 3: The LDR — the resistor that sees light →

LED LED

A light-emitting diode: a diode that gives off light when current flows through it. The longer leg is plus (anode), and it needs a series resistor to limit the current. Lesson: What actually happens when you turn ON an LED? →

M

mAh (milliamp-hour) mAh

A measure of how much charge a battery holds. 1,000 mAh can supply 1 A for one hour. For energy, multiply by the voltage: 5,000 mAh × 3.85 V ≈ 19 Wh. Lesson: Quiz #15: What does mAh on a battery mean? → B, how much… →

MCB (miniature circuit breaker) MCB

A resettable switch in a home panel that trips on overload or short circuit to protect the wiring from overheating. Lesson: MCB: overload vs short circuit →

Microcontroller MCU

A small computer on one chip, with processor, memory and input/output pins together. Examples: the ATmega328P on an Arduino Uno, the ESP32 and the RP2040. Lesson: Microcontroller vs Microprocessor →

MOSFET

A transistor switched by voltage on its gate rather than by current. It wastes very little power when fully on, so it is used to switch motors, LED strips and power supplies. Lesson: The MOSFET: big DC loads, no click →

Motor driver

A board (such as the L298N) that lets a low-power microcontroller pin switch the much larger current a motor needs, usually in both directions. Lesson: Why your motor needs a driver →

Multimeter

A handheld tester that measures voltage, current and resistance, and usually continuity (a beep) and diodes. Lesson: Workbench Skills Part 1: Meet the multimeter — every… →

N

NFC

Near-field communication: short-range wireless at 13.56 MHz that works within about 4 cm. A reader's magnetic field powers the chip in a contactless card, so the card needs no battery. Lesson: Everyday Tech Part 7 — how tap-to-pay works (NFC) →

NPU

A part of a chip built only for the multiply-and-add maths of AI, so photo and voice features run fast on very little power. Lesson: Chips Part 7: what is an NPU? The AI part of your phone chip →

O

Ohm's law V = I × R

Voltage = current × resistance. Know any two of volts, amps and ohms and you can work out the third: 5 V across 1 kΩ gives 5 mA. Lesson: Why does a resistor resist current? →

P

Parallel circuit

Parts connected side by side across the same two points. Each gets the same voltage and the currents add up; if one branch breaks, the others keep working. Lesson: Series vs parallel resistors →

PCB (printed circuit board) PCB

A board with copper tracks that connect electronic parts, replacing loose wires. Typical layers: FR-4 base, copper, solder mask and silkscreen. Lesson: PCB Design with KiCad Part 1: What is a PCB? →

Power W

How fast energy is used, measured in watts (W). Power = volts × amps, so 5 V × 2 A = 10 W. Lesson: Power: P = V × I →

Pull-up resistor

A resistor that holds an input pin HIGH until a button connects it to ground. Arduino has one built in: pinMode(pin, INPUT_PULLUP). Lesson: Control it with a BUTTON →

PWM (pulse-width modulation) PWM

Switching a pin on and off very fast and changing how long it stays on. It dims LEDs and controls motor speed; Arduino's analogWrite() uses it. Lesson: Make it FADE (PWM) →

R

RCD / RCCB / GFCI RCD

A safety switch that compares the current going out with the current coming back. If about 30 mA leaks to earth (for example through a person), it cuts the power in milliseconds. Called RCD or RCCB in Europe and India, and GFCI in the USA. Lesson: RCCB: the switch that trips on a leak →

Register

A small memory location inside a microcontroller whose bits directly control hardware. On the ATmega328P, DDRB sets pin direction, PORTB sets outputs and PINB reads inputs. Lesson: Embedded C Part 6: What is a register? →

Relay

A switch moved by an electromagnet. A small coil current switches a completely separate, larger circuit and keeps the two electrically isolated. Lesson: The RELAY: 5 V switches 230 V →

Resistance Ω

How strongly a part opposes current, measured in ohms (Ω). More resistance means less current for the same voltage. Lesson: Why does a resistor resist current? →

Resistor R

A part that limits current and turns the extra energy into heat. Its value in ohms is shown by colour bands; an LED on 5 V usually needs about 220 Ω in series. Lesson: Why does a resistor resist current? →

RMS voltage RMS

The 'equal heating' value of an AC voltage. 230 V RMS mains actually peaks at about 325 V (230 × √2); 120 V RMS peaks at about 170 V. Lesson: RMS: why 230 V really peaks at 325 V →

S

Semiconductor

A material such as silicon that conducts between a conductor and an insulator. Adding tiny amounts of other elements (doping) controls how it conducts; chips, diodes and LEDs are made from it. Lesson: Explained Simply #10: What is a semiconductor, really? →

Sensor

A part that turns something physical, such as temperature, light or distance, into an electrical signal a circuit can read. Lesson: NTC thermistor: the resistor that feels heat →

Serial Monitor

The Arduino IDE window that shows text a board sends over USB with Serial.print(). It is the easiest way to see sensor values and debug code. Lesson: Serial.print: see your knob's number →

Series circuit

Parts connected one after another in a single path. The same current flows through all of them and their resistances add up. Lesson: Series vs parallel resistors →

Servo motor

A motor with built-in gears and control electronics that turns to an exact angle set by the width of a control pulse (about 1–2 ms). Lesson: Servo motor: stop at an exact angle →

SoC (system on a chip) SoC

One chip that holds a phone's main parts together: CPU, GPU, modem, memory controller and more. Lesson: Chipset: your phone's whole computer is ONE chip →

Stepper motor

A motor that moves in fixed steps, commonly 200 steps per turn (1.8° each), so its position can be controlled exactly without a sensor. Lesson: Stepper motor: move in exact steps →

T

Thermistor (NTC) NTC

A resistor whose resistance changes with temperature. In an NTC thermistor, resistance drops as it gets hotter. Lesson: NTC thermistor: the resistor that feels heat →

Tolerance ±%

How far a part's real value may differ from its marked value. A 1 kΩ ±5 % resistor can measure anywhere from 950 Ω to 1,050 Ω. Lesson: Tolerance: is your 1 kΩ really 1 kΩ? →

Transformer

Two coils on one iron core that change AC voltage up or down. The voltage ratio equals the turns ratio; it does not work on steady DC. Lesson: How a transformer works →

Transistor BJT

A three-leg semiconductor switch or amplifier. In an NPN transistor a small base current controls a much larger collector current. Lesson: The TRANSISTOR: a tiny current switches a BIG one →

U

USB Power Delivery USB PD

A fast-charging standard where the charger and the device agree on a voltage (5, 9, 15 or 20 V) and current before power is raised. The device only takes what it asks for. Lesson: Smart Buyer #4: Phone charger — watts, USB PD and why the… →

V

Voltage V

The electrical 'push' that makes current flow, measured in volts (V). A 1.5 V AA cell pushes gently; a 230 V or 120 V wall socket pushes hard enough to be deadly.

Voltage divider

Two resistors in series that split a voltage: Vout = Vin × R2 ÷ (R1 + R2). It is used to read sensors and to scale voltages down for a microcontroller pin. Lesson: Voltage divider — create a voltage with math →

Z

Zener diode

A diode made to conduct backwards at one exact voltage (for example 5.1 V) and hold it steady. It is used as a simple voltage reference or regulator. Lesson: Electronics Basics L14: the Zener diode — a voltage that… →

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