Electronic Components Reference Guide

Understanding electronic components is essential for reading schematics, building circuits, and troubleshooting problems. This comprehensive reference covers the most common components you'll encounter in electronics projects.

Resistors

What Resistors Do

Resistors limit the flow of electrical current in a circuit. They're the most common component you'll use, found in virtually every circuit.

Key Applications:

• Current limiting (protecting LEDs, transistors)
• Voltage division (creating reference voltages)
• Pull-up/pull-down resistors (digital circuits)
• Timing circuits (with capacitors)
• Signal conditioning

Resistor Color Code Chart

Most through-hole resistors use colored bands to indicate their resistance value. Here's how to read them:

4-Band Resistor Code (Most Common):

How to Read:

1. Orient the resistor: Gold or silver tolerance band goes on the right
2. Read left to right: First two bands are digits, third is multiplier, fourth is tolerance
3. Calculate: (1st digit)(2nd digit) × multiplier = resistance in ohms

Examples:

• Brown-Black-Red-Gold: 1-0-×100 = 1,000Ω = 1KΩ ±5%
• Yellow-Violet-Orange-Gold: 4-7-×1K = 47KΩ ±5%
• Red-Red-Brown-Gold: 2-2-×10 = 220Ω ±5%
• Orange-Orange-Brown-Gold: 3-3-×10 = 330Ω ±5%

Memory Trick: "Big Boys Race Our Young Girls But Violet Generally Wins" (Black Brown Red Orange Yellow Green Blue Violet Gray White)

Common Resistor Values

Resistors come in standard values following the E12 or E24 series:

E12 Series (±10% tolerance): 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

Each value is available with multipliers: ×1, ×10, ×100, ×1K, ×10K, ×100K, ×1M

Most Common in Projects:

• 220Ω - LED current limiting (5V)
• 330Ω - LED current limiting (9V)
• 1KΩ - General purpose pull-up/pull-down
• 10KΩ - Very common in all circuits
• 100KΩ - High impedance applications
• 1MΩ - Timing circuits, biasing

Get a complete set with our Resistor Kit (33Ω to 1MΩ).

Resistor Specifications

• Resistance Value: Measured in ohms (Ω), kiloohms (KΩ), or megohms (MΩ)
• Tolerance: How much the actual value can vary (±5% is standard for hobbyists)
• Power Rating: Maximum power dissipation (1/4W is standard for through-hole)
• Temperature Coefficient: How value changes with temperature (less critical for hobbyists)

Power Calculation: P = V² / R or P = I² × R

Always use a resistor rated for at least 2× the expected power dissipation for reliability.

Capacitors

What Capacitors Do

Capacitors store electrical charge temporarily. They act like tiny rechargeable batteries that charge and discharge very quickly.

Key Applications:

• Filtering (smoothing power supply ripple)
• Coupling (passing AC signals while blocking DC)
• Decoupling/bypass (filtering noise from ICs)
• Timing circuits (with resistors)
• Energy storage (camera flash)

Types of Capacitors

1. Ceramic Capacitors (Non-polarized)

• Appearance: Small disc or rectangular SMD
• Values: 1pF to ~10µF
• Voltage: 50V typical
• Uses: Decoupling, high-frequency filtering, timing
• Polarity: None - can be installed either way

2. Electrolytic Capacitors (Polarized)

• Appearance: Cylindrical, usually with stripe marking negative side
• Values: 1µF to thousands of µF
• Voltage: Various ratings (check carefully!)
• Uses: Power supply filtering, bulk energy storage
• Polarity: CRITICAL - wrong polarity can cause explosion!
• Longer lead = Positive
• Stripe on body = Negative side

WARNING: Installing electrolytic capacitors backward can cause them to overheat, leak, or explode! Always check polarity.

3. Film/Polyester Capacitors (Non-polarized)

• Appearance: Box-shaped, often yellow or blue
• Values: 1nF to ~10µF
• Voltage: Typically high (100V+)
• Uses: Audio circuits, timing, snubbing
• Polarity: None

Capacitor Value Markings

Direct Marking: Some capacitors print the value directly: "10µF 25V"

3-Digit Code (Common on Ceramics):

• First two digits = significant figures
• Third digit = multiplier (number of zeros to add)
• Result is in picofarads (pF)

Examples:

• 104: 10 + 0000 = 100,000pF = 100nF = 0.1µF
• 223: 22 + 000 = 22,000pF = 22nF = 0.022µF
• 473: 47 + 000 = 47,000pF = 47nF = 0.047µF
• 105: 10 + 00000 = 1,000,000pF = 1µF

Capacitor Units Conversion

Capacitor values span a huge range, so multiple unit prefixes are used:

• 1 Farad (F) = 1,000,000 µF (rarely seen - huge!)
• 1 Microfarad (µF) = 1,000 nF = 1,000,000 pF
• 1 Nanofarad (nF) = 1,000 pF = 0.001 µF
• 1 Picofarad (pF) = 0.001 nF = 0.000001 µF

Common Capacitor Values

• 100nF (0.1µF): Standard decoupling capacitor (place near every IC)
• 10µF: Local power filtering
• 100µF - 1000µF: Main power supply filtering
• 22pF, 33pF: Crystal oscillator loading caps

Diodes

What Diodes Do

Diodes allow current to flow in only one direction - like a one-way valve for electricity.

Key Applications:

• Rectification (converting AC to DC)
• Reverse polarity protection
• Flyback/snubber diodes (protecting against voltage spikes)
• Signal clipping and clamping

Diode Polarity

Identifying the Cathode (Negative):

• Printed band/stripe on one end = cathode
• Current flows FROM anode TO cathode (arrow direction in schematic symbol)
• In normal operation, cathode should be at higher voltage than anode

Schematic Symbol: Triangle pointing to a line - current flows in direction of arrow

Common Diode Types

1N4001 - 1N4007 Series (Rectifier Diodes):

• General-purpose rectification
• 1A current rating
• Differences are voltage rating (1N4001=50V, 1N4007=1000V)
• Most common: 1N4007 (highest voltage rating, same price)

1N4148 (Small Signal Diode):

• Fast switching
• Small current (200mA max)
• Used in signal processing, logic circuits

Schottky Diodes (e.g., 1N5819):

• Very low forward voltage drop (0.3V vs 0.7V)
• Fast switching
• Ideal for power supplies and reverse polarity protection

Zener Diodes:

• Conduct in reverse at specific voltage (e.g., 5.1V Zener)
• Used for voltage regulation and reference

LED (Light Emitting Diode)

LEDs are special diodes that emit light when current flows through them.

LED Polarity:

• Longer lead = Anode (positive)
• Shorter lead = Cathode (negative)
• Flat edge on lens indicates cathode side
• Inside the LED, larger metal piece = cathode

ALWAYS use a current-limiting resistor with LEDs!

Standard LEDs require 10-20mA. Calculate resistor value:

R = (V_supply - V_LED) / I_LED

Examples:

• 5V supply, red LED (1.8V drop), 15mA: R = (5 - 1.8) / 0.015 = 213Ω → use 220Ω
• 9V supply, white LED (3.2V drop), 15mA: R = (9 - 3.2) / 0.015 = 387Ω → use 390Ω

Typical LED Forward Voltages:

• Red: 1.8-2.0V
• Yellow/Green: 2.0-2.2V
• Blue/White: 3.0-3.4V
• Infrared: 1.2-1.5V

Transistors

What Transistors Do

Transistors act as electronic switches or amplifiers. They're the fundamental building block of all modern electronics.

Key Applications:

• Electronic switches (controlling high current with low current)
• Signal amplification
• Logic gates (billions in every microprocessor)
• Oscillators and timing circuits

BJT (Bipolar Junction Transistor)

Two Types:

• NPN: Most common; turns ON when base is HIGH
• PNP: Turns ON when base is LOW

Three Pins:

• Base (B): Control input (like a gate)
• Collector (C): Current enters here
• Emitter (E): Current exits here

Pin Identification: Unfortunately, pinouts vary by part number. ALWAYS check the datasheet!

Common NPN Transistors:

• 2N3904: General purpose, small signal, 200mA max
• 2N2222: Higher current (800mA), switching and amplification
• TIP120: Darlington transistor, very high gain, up to 5A

Common PNP Transistors:

• 2N3906: Complement to 2N3904
• 2N2907: Complement to 2N2222

MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor)

MOSFETs are voltage-controlled (vs current-controlled BJTs) and can handle much higher currents.

Three Pins:

• Gate (G): Control input (voltage-controlled, draws almost no current)
• Drain (D): Current enters
• Source (S): Current exits

Two Types:

• N-Channel: Most common; turns ON when gate is HIGH relative to source
• P-Channel: Turns ON when gate is LOW relative to source

Common MOSFETs:

• 2N7000: Small N-channel, 200mA, great for logic-level switching
• IRF540N: High power N-channel, 33A, motor control
• IRF9540N: High power P-channel, 23A

Integrated Circuits (ICs)

What ICs Are

Integrated Circuits contain complete circuits with many transistors, resistors, and other components in one package.

Common IC Packages

• DIP (Dual Inline Package): Two rows of pins, breadboard-friendly
• SOIC (Small Outline IC): Surface mount version of DIP
• QFP (Quad Flat Pack): Pins on all four sides
• BGA (Ball Grid Array): Connections on bottom (very difficult to hand-solder)

Pin 1 Identification

ICs must be oriented correctly. Pin 1 is marked by:

• Small dot or dimple on the package near pin 1
• Notch or semicircle at one end (pin 1 is to the left of the notch)
• Pins are numbered counterclockwise from pin 1 when viewed from top

Popular Beginner ICs

555 Timer:

• Most popular IC ever made
• Creates timing pulses, oscillators, delays
• 8-pin DIP package
• Can blink LEDs, make sounds, create PWM

741 Op-Amp:

• Operational amplifier (programmable gain)
• Signal amplification, filtering, math operations
• 8-pin DIP

7805 Voltage Regulator:

• Converts varying input voltage to stable 5V output
• 1A current capability
• 3-pin TO-220 package
• Common in power supplies

74 Series Logic ICs:

• Digital logic gates (AND, OR, NOT, NAND, etc.)
• Foundation of digital electronics
• Example: 7404 (hex inverter), 7408 (quad AND gate)

Other Essential Components

Potentiometers (Variable Resistors)

• 3 terminals: Two ends of resistive element, center is wiper (variable contact)
• Types: Rotary (knob) or linear (slider)
• Taper: Linear (B) or logarithmic (A, for audio volume controls)
• Common values: 10KΩ most versatile
• Uses: Volume controls, voltage dividers, analog input

Switches

Common Switch Types:

• SPST (Single Pole Single Throw): Simple on/off switch
• SPDT (Single Pole Double Throw): Selects between two connections
• DPDT (Double Pole Double Throw): Two independent SPDT switches in one
• Momentary: Returns to off when released (push buttons)
• Latching: Stays in position (toggle switches)

Crystals and Resonators

• Provide precise timing for microcontrollers and digital circuits
• Common frequencies: 16MHz (Arduino), 32.768kHz (RTC)
• Usually require loading capacitors (typically 22pF each)

Fuses

• Protective device that breaks circuit if current exceeds rating
• ALWAYS use appropriate fuse in power supplies
• Types: Glass tube, blade (automotive), SMD
• Never replace with higher rating or bypass!

Component Datasheets

Datasheets are your best friend! They contain all specifications, pinouts, and application notes.

How to Read a Datasheet:

1. Absolute Maximum Ratings: NEVER exceed these or you'll destroy the part
2. Recommended Operating Conditions: Normal use parameters
3. Electrical Characteristics: Actual performance specifications
4. Pinout Diagram: Physical pin locations and functions
5. Application Notes: Example circuits and design tips
6. Package Dimensions: Physical size for PCB layout

Where to Find Datasheets:

• Google "component part number datasheet"
• Manufacturer websites
• DigiKey, Mouser, Octopart (cross-reference databases)

Component Storage and Organization

Proper organization saves enormous time:

• Resistors: Sort by value in labeled compartments or labeled bags
• Capacitors: Separate by type (ceramic, electrolytic, film) and value
• Semiconductors: Keep in anti-static bags or foam; label clearly
• ICs: Store in anti-static tubes or foam; note orientation
• Small parts: Use component storage boxes with adjustable dividers
• Label everything: Future you will thank present you!

Testing Components

Your multimeter can test most components:

Testing Resistors

• Set multimeter to resistance (Ω) mode
• Touch probes to both leads
• Reading should be within tolerance of color code
• If infinite resistance: resistor is open (failed)

Testing Diodes

• Use diode test mode (diode symbol) or resistance mode
• Forward bias: Should show 0.5-0.7V drop
• Reverse bias: Should show infinite resistance or "OL"
• If same reading both ways: diode is shorted (failed)

Testing Capacitors

• Discharge first! Short the leads safely
• Capacitance mode: Should read close to marked value
• Resistance mode: Should start low and rise to infinity as cap charges
• If stays low: capacitor is shorted (failed)
• If immediately infinite: may be open (failed) or just small value

Testing Transistors

• Use transistor hFE test mode if available
• Alternatively, use diode mode to test B-E and B-C junctions
• NPN: Both junctions should conduct when red probe on base
• PNP: Both junctions should conduct when black probe on base

Quick Reference: Component Symbols

Schematic symbols you must know:

• Resistor: Zigzag line or rectangle
• Capacitor (non-polarized): Two parallel lines
• Capacitor (polarized): Two parallel lines, one curved (negative side)
• Diode: Triangle pointing to line
• LED: Diode with arrows pointing outward
• NPN Transistor: Arrow pointing OUT of emitter
• PNP Transistor: Arrow pointing INTO emitter
• Ground: Three horizontal lines decreasing in length
• Power (Vcc/Vdd): Circle or arrow pointing up
• Switch: Angled line that completes/breaks connection

Getting Started with Components

Recommended Component Kits:

• Resistor Kit - Complete range from 33Ω to 1MΩ
• Make: Electronics Component Packs - Curated selection for guided learning
• Make: Electronics Ultimate Kit - Everything needed for comprehensive education

Continue Learning:

• Beginner's Guide to Electronics - Start with the fundamentals
• How to Solder Tutorial - Assemble components properly
• Make: Electronics Book Guide - Structured learning path

Master component identification and you'll be able to read schematics, build circuits, and troubleshoot problems like a pro!