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Electronic Components β€” Complete Guide & Cheat Sheet

Last reviewed: 2026-09-01

[!NOTE] This article covers the components presented in the video "All Electronic Components Explained In a SINGLE VIDEO" by Ron Mattino (watch on YouTube). The video transcript could not be fetched (YouTube blocks requests from this server's IP), so the content is compiled from the video's subject matter plus standard electronics reference knowledge. The summary table at the end is designed as a one-page cheat sheet.

Overview

Every electronic circuit β€” from an ESP32 sensor node to a 10 kW solar inverter β€” is built from a small set of fundamental components. This guide explains the most common ones: what they do, how to identify them, how to read their markings, and how to test them with a multimeter.

Components fall into two broad families:

  • Passive components β€” cannot amplify or switch; they only consume, store, or transfer energy (resistors, capacitors, inductors, transformers, fuses).
  • Active components β€” can amplify or switch signals using an external power supply (diodes, transistors, MOSFETs, op-amps, regulators, ICs).

Passive Components

Resistor (R)

Limits current flow and sets voltage levels. The most common component in any circuit.

  • Unit: Ohm (Ξ©). Common ranges: 1 Ξ© to 10 MΞ©.
  • Markings: axial resistors use 4- or 5-band color code; SMD resistors use 3- or 4-digit codes (e.g. 472 = 47 Γ— 10Β² = 4.7 kΞ©).
  • Power rating: 1/8 W, 1/4 W, 1/2 W, 1 W… determines physical size. Power dissipated: P = IΒ² Γ— R.
  • Variants: potentiometer (adjustable, 3 legs), trimpot, thermistor (temperature-sensitive), LDR (light-sensitive), varistor/MOV (voltage spike protection).

[!TIP] 4-band resistor color code Black 0, Brown 1, Red 2, Orange 3, Yellow 4, Green 5, Blue 6, Violet 7, Grey 8, White 9 β€” then multiplier band (same colors = Γ—10ⁿ), then tolerance (gold = Β±5%, silver = Β±10%). Example: Red–Red–Orange–Gold = 22 Γ— 10Β³ = 22 kΞ© Β±5%.

Capacitor (C)

Stores energy in an electric field. Used for filtering, decoupling, timing, and smoothing.

  • Unit: Farad (F) β€” practically Β΅F, nF, pF.
  • Polarized types: electrolytic (aluminium) and tantalum β€” must be wired the right way round (longer leg = +). Reversed polarity = explosion risk.
  • Non-polarized types: ceramic, film, mica β€” safe either way.
  • Markings: electrolytic β†’ value + voltage (e.g. 100Β΅F 25V); ceramic β†’ 3-digit code (e.g. 104 = 100 nF); film β†’ direct value.
  • Key behavior: blocks DC, passes AC. Voltage rating must exceed circuit voltage.

Inductor (L)

Stores energy in a magnetic field. Used in power supplies (buck/boost converters), filters, and RF circuits.

  • Unit: Henry (H) β€” practically Β΅H, mH.
  • Behavior: opposes changes in current. Never interrupt current through an inductor abruptly β€” the voltage spike can destroy components (hence flyback diodes across relay/motor coils).
  • Markings: often color bands (like resistors) or printed code.

Transformer (T)

Two or more coupled inductors that transfer AC energy between circuits via magnetic coupling.

  • Purpose: step up/down AC voltage, isolate circuits galvanically.
  • Only works with AC β€” a DC voltage on the primary does nothing (and can burn it).
  • Ratio: Vβ‚‚/V₁ = Nβ‚‚/N₁ (turns ratio).

Semiconductors

Diode (D)

Allows current in one direction only (from anode β†’ cathode).

  • Forward voltage (Vf): ~0.6-0.7 V silicon, ~0.3 V Schottky, ~2-3.5 V LED.
  • Uses: rectification (ACβ†’DC), reverse-polarity protection, flyback protection, voltage clamping.
  • Marking: a line on the body marks the cathode (βˆ’).
  • Variants: Schottky (fast, low Vf), Zener (reverse-breakdown voltage regulation), TVS (transient protection).

LED (D, light-emitting diode)

Diode that emits light.

  • Always needs a series resistor (unless in a designed module).
  • Resistor formula: R = (V_supply βˆ’ V_LED) / I_LED β€” e.g. 5 V supply, red LED (2 V, 20 mA): R = (5βˆ’2)/0.02 = 150 Ξ©.
  • Long leg = anode (+).

Zener Diode

Deliberately operated in reverse breakdown to hold a stable voltage.

  • Example: a 5.1 V Zener keeps a node at ~5.1 V regardless of small supply variations β€” cheap voltage reference / shunt regulator.
  • Cathode marking like a normal diode; used in reverse.

Bipolar Junction Transistor β€” BJT (Q)

Current-controlled switch or amplifier. Three legs: Base, Collector, Emitter.

  • NPN (most common): small current into the Base switches a larger Collectorβ†’Emitter current. Emitter is the arrow point on the symbol.
  • PNP: opposite polarity β€” current flows out of the base; emitter arrow points in.
  • Key rule (NPN): V_BE β‰ˆ 0.7 V to turn on; base current I_B β‰ˆ I_C / h_FE.
  • Uses: switching loads (relays, LEDs, motors), simple amplifiers, level shifting.
  • Package markings: 2N2222, BC547, S8050, etc.

MOSFET (Q)

Voltage-controlled switch β€” the workhorse of power electronics (inverters, motor drivers, solar charge controllers).

  • Three legs: Gate, Drain, Source. Voltage on Gate controls Drain↔Source conduction β€” almost no gate current.
  • N-channel vs P-channel; enhancement (normally off) is the common type.
  • Key specs: V_GS(th) (threshold), R_DS(on) (on-resistance β€” low = less heat), V_DS max, I_D max.
  • Static-sensitive β€” handle with care (ESD can punch the gate oxide).

Thyristor / SCR & Triac

  • SCR: one-way latching switch β€” once triggered by the gate, it stays on until current drops to zero (used in AC power control, crowbar protection).
  • Triac: bidirectional SCR (controls AC in both halves of the cycle β€” dimmers, motor speed).

Optocoupler / Optoisolator

LED + phototransistor in one package β€” transfers a signal across an isolation barrier (no electrical connection).

  • Uses: isolating MCU from high-voltage/inductive circuits, level shifting, protecting logic inputs.

Integrated Circuits (IC)

Operational Amplifier β€” Op-Amp (U)

High-gain differential amplifier: amplifies the difference between its two inputs.

  • Two inputs: inverting (βˆ’) and non-inverting (+), one output.
  • Common configurations:
  • Voltage follower (buffer): output = input, high input impedance, low output impedance.
  • Non-inverting amplifier: gain = 1 + Rβ‚‚/R₁.
  • Inverting amplifier: gain = βˆ’Rβ‚‚/R₁.
  • Comparator: output swings HIGH/LOW depending on which input is higher.
  • Examples: LM358, LM741, TL072, LM393 (comparator).

555 Timer (U)

The classic timing IC β€” monostable (one-shot) and astable (oscillator) modes.

  • Astable formula: f = 1.44 / ((R₁ + 2Rβ‚‚) Γ— C) β€” square-wave generator, LED flashers, buzzers, PWM.
  • Also used for debouncing, timers, tone generation.

Voltage Regulator (U)

Maintains a stable output voltage regardless of input variations and load.

  • Fixed linear: 7805 (+5 V), 7812 (+12 V), 7905 (βˆ’5 V) β€” simple but wasteful (drops the difference as heat).
  • Adjustable: LM317 β€” V_out = 1.25 Γ— (1 + Rβ‚‚/R₁).
  • LDO: low-dropout, efficient for battery applications.
  • Switching regulators (buck/boost): highly efficient (90%+), used in most modern power supplies.

Microcontroller (U)

A programmable computer on a chip (Arduino/ATmega, ESP32, STM32, Raspberry Pi Pico).

  • Runs firmware from flash, reads sensors (ADC), drives outputs (GPIO, PWM), communicates (UART, IΒ²C, SPI).
  • Needs supporting components: decoupling capacitors, crystal/resonator (or internal RC), pull-up resistors, voltage regulation.

Electromechanical Components

Relay (K)

Electromagnetic switch: a small current energizes a coil that closes/opens contacts carrying a much larger current.

  • Coil specs: 5 V / 12 V / 24 V versions.
  • Always add a flyback diode across the coil (cathode toward +) to absorb the inductive spike when switching off β€” otherwise it can kill the driving transistor/MCU pin.

Switch (S)

  • SPST / SPDT / DPDT β€” number of poles (circuits) and throws (positions).
  • Momentary (push-button, returns when released) vs latching (stays).
  • Tactile, toggle, rocker, slide, micro-switch (limit), reed (magnetic), DIP (configuration banks).

Fuse & Circuit Breaker (F)

Overcurrent protection β€” the last line of defense.

  • Fuse: one-time, rated in A and voltage (e.g. 5Γ—20 mm glass, blade/ANL for automotive, mini-fuse). Never replace with a higher rating.
  • PTC resettable fuse: self-resetting β€” heats up and opens, cools and reconnects.
  • Circuit breaker: manual reset, reusable.
  • Sizing rule: fuse β‰ˆ 1.25 Γ— maximum continuous current.

Motors

  • DC motor: spins when powered β€” speed ∝ voltage, current ∝ load. Needs a driver (MOSFET H-bridge) for direction/speed.
  • Servo: position-controlled (PWM pulse every ~20 ms; 1 ms β‰ˆ 0Β°, 1.5 ms β‰ˆ 90Β°, 2 ms β‰ˆ 180Β°).
  • Stepper: moves in precise steps β€” for 3D printers, CNC; needs a driver (A4988, DRV8825).

Buzzer

  • Active: generates its own tone when powered (just apply DC).
  • Passive: needs an external square wave (PWM) β€” can play melodies.

Sensors & Other Common Parts

Part What it senses Behavior Typical use
LDR (photoresistor) Light Resistance drops in bright light (MΞ© β†’ kΞ©) Night lights, light meters
Thermistor NTC/PTC Temperature NTC: resistance drops when hot; PTC: rises Motor protection, temp sensing
Hall sensor Magnetic field Digital or analog output RPM sensing, door/window sensors
PIR sensor Infrared motion HIGH when motion detected Security, presence
Potentiometer β€” Adjustable voltage divider Volume knobs, calibration
Crystal / Resonator β€” Precise frequency reference (e.g. 16 MHz) MCU clocking, RTC
Capacitor (decoupling) β€” Local energy reservoir near ICs Noise suppression, stability

πŸ“‹ Cheat Sheet β€” All Components at a Glance

Component Ref. Category What it does Key property / unit How to test (multimeter)
Resistor R Passive Limits current, sets voltage Resistance, Ξ© Ohmmeter: read value vs color code (Β±tolerance)
Potentiometer RV Passive Adjustable resistor / voltage divider Ξ© (max) Ohmmeter between wiper and ends while turning
Capacitor C Passive Stores charge, filters, blocks DC Capacitance, F (Β΅F/nF/pF) Ohmmeter: brief continuity then open (charging); ESR meter for precision
Electrolytic capacitor C Passive (polarized) Bulk energy storage, smoothing Β΅F + voltage rating Check no short, correct polarity; bulged top = dead
Inductor L Passive Stores magnetic energy, filters Inductance, H (Β΅H/mH) Ohmmeter: near 0 Ξ© (low DCR); no continuity = open
Transformer T Passive AC voltage step up/down, isolation Turns ratio Ohmmeter: continuity on each winding; check isolation between windings
Fuse F Protection Opens on overcurrent Amps, A Ohmmeter: ~0 Ξ© = good; OL = blown
Diode D Active One-way current valve Vf ~0.6 V (Si) Diode mode: ~0.6 V one way, OL the other
LED D Active Emits light Vf 2-3.5 V, I ~20 mA Diode mode: glows faintly; OL in reverse
Zener diode D Active Voltage reference/regulation Breakdown Vz Diode mode forward; reverse ~Vz with bench supply
BJT transistor Q Active Current-controlled switch/amp h_FE, V_BE ~0.7 V Diode mode: B–E and B–C junctions ~0.6-0.7 V
MOSFET Q Active Voltage-controlled switch V_GS(th), R_DS(on) Diode mode: body diode D–S one way; gate open
SCR / Triac Q Active Latching AC power switch Hold current, gate trigger Diode mode between anode/cathode; gate pulses
Optocoupler U Active Signal isolation CTR (transfer ratio) Power input LED, check output transistor switches
Op-Amp U IC Amplify/compare signals Gain, GBW Supply it, test follower/comparator behavior
555 timer U IC Timing, oscillation Frequency formula Wire astable, measure square wave with scope
Voltage regulator U IC Stable output voltage V_out, dropout Measure in/out; 78xx out = rated V Β±5%
Microcontroller U IC Programmable logic Clock, flash, GPIO Program it, check power pins, blink LED
Relay K Electromechanical Big switch, small control Coil V, contact A Ohmmeter: coil 50-200 Ξ©; click on coil power
Switch / button S Electromechanical Open/close circuit Poles, throws Ohmmeter: continuity in closed state
DC motor M Electromechanical Rotation V, current, RPM Ohmmeter: low Ξ© between terminals; spins with supply
Servo M Electromechanical Position control PWM pulse width PWM signal β†’ shaft angle follows
Stepper M Electromechanical Precise steps Steps/rev, coil Ξ© Ohmmeter: coil pairs have continuity; driver needed
Buzzer BZ Electromechanical Sound Active/passive Active: beeps on DC; passive: needs PWM
LDR R Sensor Light β†’ resistance kΩ–MΞ© Ohmmeter: resistance drops under light
Thermistor R Sensor Temp β†’ resistance NTC/PTC, 10 kΞ© @25 Β°C Ohmmeter: resistance changes with heat/cold
Hall sensor U Sensor Magnetic field Digital/analog out Magnet near β†’ output toggles
Crystal Y Passive Frequency reference MHz Oscilloscope (in circuit); can't test with ohmmeter

Quick Formulas

Formula Purpose
V = I Γ— R (Ohm's law) Voltage, current, resistance
P = V Γ— I = IΒ² Γ— R Power dissipation
V_divider = V_in Γ— Rβ‚‚/(R₁+Rβ‚‚) Voltage divider
R_LED = (V_supply βˆ’ V_LED) / I_LED LED series resistor
Ο„ = R Γ— C RC time constant (~63% charge in 1Ο„; 5Ο„ = settled)
f = 1.44 / ((R₁ + 2Rβ‚‚) Γ— C) 555 astable frequency
V_out = 1.25 Γ— (1 + Rβ‚‚/R₁) LM317 adjustable regulator
P = IΒ² Γ— R (fuse sizing) Fuse β‰ˆ 1.25 Γ— max continuous current

Practical Tips

  • Polarity first: electrolytic capacitors, LEDs, diodes, and most ICs are polarized β€” check before powering. A reversed electrolytic can pop.
  • Decouple every IC: place a 100 nF ceramic capacitor as close as possible to each IC's power pins.
  • Flyback diode on every inductive load (relay coil, motor, solenoid) β€” cathode toward the positive supply.
  • MOSFETs and CMOS ICs are ESD-sensitive β€” use an anti-static wrist strap or at least touch ground before handling.
  • Check polarity with a multimeter in diode mode before connecting power β€” seconds of checking saves components.
  • Derate: choose capacitors rated β‰₯1.5Γ— the circuit voltage and resistors rated β‰₯2Γ— the expected power.

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