594  Conductors, Insulators, and Semiconductors

594.1 Conductors, Insulators, and Semiconductors

⏱️ ~15 min | ⭐ Foundational | 📋 P06.C05.U01

Materials behave differently when it comes to conducting electricity:

594.1.1 Electronic Components Taxonomy

Before diving into materials, let’s understand how electronic components are classified in IoT systems:

Graph diagram

Graph diagram
Figure 594.1: Electronic components taxonomy showing passive components (resistors, capacitors, inductors) that cannot amplify signals, active components (diodes, transistors, thyristors) that can control and amplify current, and integrated circuits that combine thousands to billions of components into complete systems like sensors, microcontrollers, and wireless modules

The three passive components—resistors, capacitors, and inductors—behave differently in circuits. Understanding their properties is essential for IoT design.

Property Resistor (R) Capacitor (C) Inductor (L)
Circuit Symbol ⏛ (zigzag) ⏥ (parallel plates) ⏚ (coil)
I-V Relationship V = R·I I = C·dV/dt V = L·dI/dt
Unit Ohm (Ω) Farad (F) = C/V Henry (H) = V·s/A
Impedance Z Z = R Z = 1/(j2πfC) Z = j2πfL
Power Loss P = I²R = V²/R 0 (ideal) 0 (ideal)
Energy Storage 0 (dissipates heat) W = ½CV² W = ½LI²
Frequency Response Constant Passes high freq, blocks DC Passes DC, blocks high freq

Why This Matters for IoT:

Component IoT Application Example
Resistor Current limiting, voltage dividers, pull-ups LED current limiting (220Ω), sensor pull-up (4.7kΩ)
Capacitor Power filtering, decoupling, timing 100nF decoupling on MCU VCC, 1000µF bulk capacitor
Inductor EMI filtering, DC-DC conversion, antennas Switching regulator, PCB antenna matching

Key Formulas for IoT Design:

  • RC Time Constant: τ = R × C (seconds)
    • Used for: Button debouncing, ADC sample timing
    • Example: 10kΩ × 100nF = 1ms
  • LC Resonant Frequency: f = 1/(2π√(LC))
    • Used for: RF tuning, antenna matching
    • Example: 1µH × 10pF → 50MHz
  • Capacitor Energy: W = ½CV²
    • Used for: Backup power calculations
    • Example: 1000µF × 3.3V² = 5.4mJ (powers MCU for ~50ms during brownout)
NoteComponent Quick Reference

594.1.2 Schematic Symbol to Real Component Guide

Learning to read schematics requires mapping symbols to physical components:

Component Symbol Description Physical Appearance Key Specs to Know
Resistor Zigzag line or rectangle Cylinder with color bands Ohms (Ω), Power rating (W)
Capacitor Two parallel lines Cylinder or disc Capacitance (µF), Voltage rating
LED Triangle with arrow + light rays Clear/colored dome Forward voltage (Vf), Max current
Transistor Circle with 3 leads (NPN/PNP) TO-92 or SMD package hFE (gain), Vce max
Diode Triangle pointing to line Glass cylinder with stripe Forward voltage, Max current
Inductor Coiled line Wire-wound cylinder Inductance (µH/mH)

Reading color codes (resistors): - Black=0, Brown=1, Red=2, Orange=3, Yellow=4 - Green=5, Blue=6, Violet=7, Gray=8, White=9 - Gold=5% tolerance, Silver=10%

Example: Brown-Black-Red = 10 × 10² = 1000Ω = 1kΩ

594.1.3 IoT Component Visual Dictionary

Comprehensive visual dictionary of electronic components used in IoT systems, organized by category. Shows passive components (resistors with color code bands, capacitors of various types including electrolytic and ceramic, inductors), active components (transistors in TO-92 and SMD packages, MOSFETs, op-amps), power components (voltage regulators, DC-DC converters), and protection components (diodes, fuses, TVS devices). Each component is shown with its schematic symbol, physical appearance, and typical IoT application examples.

Electronic components for IoT systems
Figure 594.2: AI-generated visual dictionary of electronic components commonly used in IoT applications

A comprehensive reference guide for selecting and using electronic components in IoT projects. This section provides practical specifications and real-world use cases.

594.1.3.1 Essential Passive Components

Component Symbol Function IoT Use Case Typical Values
Resistor ─/\/\/─ Limits current flow LED current limiting 220Ω-10kΩ
Capacitor ─ǁ─ Stores electrical charge Power supply smoothing 100nF-1000µF
Inductor ─∿∿∿─ Stores magnetic energy Switching regulators, EMI filtering 10µH-100mH
Diode ─▷│─ One-way current flow Reverse polarity protection 1N4001, 1N4148
LED ─▷│─ (light) Light output Status indicators, displays Red: 1.8-2.2V, Blue: 3.0-3.4V

Passive Component Selection Rules:

  • Resistors: Always check power rating (P = I² × R). Common: 1/8W, 1/4W, 1/2W
  • Capacitors: Voltage rating must be ≥ 2× operating voltage for reliability
  • Inductors: Saturation current must exceed maximum expected current
  • Diodes: Forward voltage (Vf) affects efficiency; Schottky diodes have lower Vf (0.3V vs 0.7V)
  • LEDs: Always use current-limiting resistor. Formula: R = (Vsupply - Vf) / Iled

594.1.3.2 Essential Active Components

Component Function IoT Use Case Popular Parts Key Specs
Transistor (NPN) Switch/amplify small signals Driving motors, relays 2N2222, BC547 Ic=800mA, hFE=100-300
Transistor (PNP) High-side switching Load switching 2N2907, BC557 Ic=600mA, hFE=100-300
MOSFET (N-channel) High-current power switching Motors, LED strips, solenoids IRF540, AO3400 Id=10-30A, RDS(on)=0.01-0.1Ω
MOSFET (P-channel) High-side load control Reverse polarity protection IRF9540, AO3401 Id=10-20A, higher RDS(on)
Op-Amp Signal conditioning Sensor amplification, filtering LM358, MCP6002 Rail-to-rail, low offset
Voltage Regulator (Linear) Stable DC voltage 3.3V/5V from battery AMS1117, LM7805 Dropout: 1-1.5V, efficiency 50-60%
Voltage Regulator (Switching) Efficient power conversion Battery-powered IoT nodes TPS62130, LM2596 Efficiency: 85-95%, lower quiescent current

Active Component Selection Rules:

  • BJT vs MOSFET: Use BJT for <1A, MOSFET for >1A (lower switching losses)
  • Logic-Level MOSFETs: Required for 3.3V/5V GPIO control (Vgs(th) < 2.5V)
  • Op-Amp Power: Choose rail-to-rail for single-supply IoT applications
Geometric illustration of capacitor types showing ceramic disc capacitor with small form factor for decoupling, electrolytic capacitor with polarity markings for power supply filtering, tantalum capacitor for stable capacitance, and film capacitor for signal coupling applications
Figure 594.3: Capacitors store electrical charge and are essential for power supply filtering, signal coupling, and timing circuits. Ceramic capacitors offer compact size for high-frequency bypass, while electrolytic capacitors provide large capacitance values for voltage stabilization in IoT power circuits.
Artistic reference table showing common capacitor, inductor, and resistor packages with physical dimensions, typical values, power ratings, and recommended IoT applications for each component type
Figure 594.4: This component reference table summarizes specifications for passive components commonly used in IoT designs. Selecting appropriate package sizes and ratings ensures reliable operation while minimizing board space for compact sensor nodes.
Geometric diagram of inductor types showing axial through-hole inductor for power filtering, toroidal core inductor for EMI suppression, surface mount chip inductor for compact designs, and coupled inductors for DC-DC converters
Figure 594.5: Inductors store energy in magnetic fields and are critical for switching power supplies, EMI filtering, and sensor signal conditioning. The core material and geometry determine frequency response and saturation characteristics important for IoT power management.
Artistic reference of resistor schematic symbols including standard zigzag symbol, variable resistor potentiometer symbol, thermistor symbol with T marking, photoresistor symbol with light arrows, and color code band reference for determining resistance values
Figure 594.6: Understanding resistor schematic symbols enables quick circuit reading. Standard fixed resistors use the zigzag symbol, while variable resistors show an arrow. Temperature-sensitive thermistors and light-sensitive photoresistors have distinctive markings indicating their sensor functionality.
Geometric comparison of resistor package types showing carbon film axial resistor with color bands, metal film precision resistor, surface mount chip resistor with size codes, and high-power wirewound resistor for current sensing applications
Figure 594.7: Different resistor types suit various IoT applications. Carbon film resistors offer low cost for general use, metal film provides better precision for sensor circuits, surface mount enables compact PCB designs, and wirewound resistors handle high-power applications like current sensing.
  • Linear vs Switching Regulator: Linear for low noise (<100mA), Switching for efficiency (>100mA)

594.1.3.3 Common IoT Circuit Patterns

These circuit patterns solve 90% of IoT interface challenges:

Circuit Pattern Purpose When to Use Formula/Notes
Voltage Divider Scale voltage down Sensor output > ADC range, 5V→3.3V level shift Vout = Vin × (R2 / (R1 + R2))
Pull-up Resistor Ensure defined logic HIGH I2C, open-drain outputs, buttons 4.7kΩ-10kΩ typical, lower for faster switching
Pull-down Resistor Ensure defined logic LOW GPIO floating inputs, reset pins 10kΩ-100kΩ typical
Decoupling Capacitor Reduce power supply noise Every IC power pin 100nF ceramic + 10µF electrolytic
Level Shifter Bidirectional 3.3V ↔︎ 5V I2C, SPI, UART voltage mismatch Use BSS138 MOSFET or TXS0108E IC
Current Limiting (LED) Prevent LED burnout All LED circuits R = (Vsupply - Vf) / Iled
Flyback Diode Suppress inductive kickback Motors, relays, solenoids 1N4001-1N4007 across coil
RC Low-Pass Filter Remove high-frequency noise Analog sensor inputs fc = 1 / (2π × R × C)

594.1.3.4 Quick IoT Component Selection Guide

For Beginners - Start Here:

Goal Component Combo Example Circuit
Status indicator LED + Resistor GPIO → 220Ω resistor → LED → GND
Speed control Transistor + Motor GPIO → 1kΩ → NPN base, Motor between Vcc and collector
Stable power Capacitor + Regulator Battery → AMS1117-3.3 → 10µF cap → ESP32
Sensor interface Voltage divider 5V sensor → 10kΩ → ADC pin → 10kΩ → GND
High-current load MOSFET + Gate resistor GPIO → 100Ω → MOSFET gate, Load between Vcc and drain

594.1.3.5 Component Rating Guidelines

Critical Safety Rules - Prevent Component Damage:

Parameter Selection Rule Example Why It Matters
Voltage Rating Choose ≥ 2× expected voltage 12V supply → use 25V+ capacitor Voltage spikes can exceed nominal
Current Rating Choose ≥ 1.5× expected current 1A motor → use 1.5A+ transistor Prevent overheating and failure
Power Rating (Watts) Must exceed P = I² × R or P = V × I 5V, 20mA LED → R=150Ω → P=0.1W → use 1/4W (0.25W) resistor Insufficient rating → burnout
Temperature Rating Match environment Outdoor sensor: -40°C to +85°C rated components Consumer-grade (0-70°C) fails in harsh conditions
Package Size Consider PCB design 0402, 0805 (SMD) or through-hole Smaller = harder to hand-solder

Real-World Temperature Derating:

  • Commercial: 0°C to 70°C (indoor IoT devices)
  • Industrial: -40°C to 85°C (outdoor sensors, automotive)
  • Military: -55°C to 125°C (extreme environments)

Common Mistakes to Avoid:

  1. ❌ “Any resistor will work” → ✓ Calculate exact value and power rating
  2. ❌ Using 5V sensor with 3.3V ADC directly → ✓ Add voltage divider or level shifter
  3. ❌ Connecting motor directly to GPIO → ✓ Use transistor/MOSFET switch
  4. ❌ Forgetting flyback diode on relay → ✓ Always add 1N4007 across coil
  5. ❌ No decoupling capacitor on MCU → ✓ Add 100nF at each Vcc pin

594.1.3.6 Quick Component Calculations

LED Current Limiting:

Given: ESP32 GPIO (3.3V), Red LED (Vf=2.0V), desired current 10mA
R = (Vsupply - Vf) / I = (3.3 - 2.0) / 0.010 = 130Ω → use 150Ω (standard value)
Power: P = I² × R = (0.01)² × 150 = 0.015W → use 1/8W resistor

Voltage Divider for 5V→3.3V:

Given: 5V sensor output, 3.3V max ADC input
Vout = Vin × (R2 / (R1 + R2))
3.3 = 5 × (R2 / (R1 + R2))
Choose R2 = 10kΩ, then R1 = 5.15kΩ → use 5.1kΩ (standard value)
Verify: 5 × (10k / (5.1k + 10k)) = 3.31V ✓

Decoupling Capacitor Value:

Rule of thumb: C = I × t / ΔV
For MCU drawing 100mA with 10ns switching, allow 0.1V droop:
C = 0.1 × 10×10⁻⁹ / 0.1 = 10nF → use 100nF for safety margin

Component Selection Summary Table:

Scenario Recommended Components Key Specs Notes
Low-current indicator (<20mA) Standard LED + resistor 220Ω-1kΩ, 1/8W Simple and reliable
Medium current load (100mA-1A) NPN transistor (2N2222) Ic=800mA, hFE>100 Add base resistor
High current load (>1A) Logic-level N-MOSFET RDS(on)<0.1Ω, Vgs(th)<2.5V IRF540, IRLZ44N
Inductive load (motor, relay) MOSFET + flyback diode 1N4007 diode Prevents voltage spikes
3.3V from battery (low noise) Linear LDO regulator AMS1117-3.3, 1A max Simple, low noise
3.3V from battery (efficient) Buck converter TPS62130, 85-95% efficient Longer battery life
Sensor signal amplification Rail-to-rail op-amp LM358, MCP6002 Single supply compatible
5V↔︎3.3V bidirectional Logic level shifter IC TXS0108E, BSS138 I2C, SPI safe conversion

Pro Tips for Component Selection:

  1. Start with reference designs: Most sensor/module datasheets include recommended circuits
  2. Use standard values: Resistors (E12 series: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82)
  3. Buy assortment kits: Get common values (resistors, capacitors, transistors) for prototyping
  4. Check package availability: Through-hole for breadboarding, SMD for final PCB
  5. Read the datasheet: Absolute maximum ratings, recommended operating conditions, typical circuits

Every IoT device follows a similar block architecture, regardless of whether it’s a simple sensor node or complex gateway:

%% fig-alt: "Generic IoT device block diagram showing six major subsystems: Wireless Transceiver (antenna, RF front-end), Energy Management (battery, solar panel, power regulation showing 1000mAh battery with 11.4µA sleep current), Accelerators and Microcontroller (CPU, hardware accelerators), Memory (RAM, Flash), Mixed-Signal Interfaces (ADC, DAC, GPIO), and Sensors/Actuators (physical world interface). All blocks interconnected via internal buses."
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flowchart TB
    subgraph device["IoT Device Architecture"]
        ANT["📡 Wireless<br/>Transceiver"]
        MCU["🧠 Accelerators &<br/>Microcontroller"]
        MEM["💾 Memory<br/>(RAM + Flash)"]
        PWR["🔋 Energy<br/>Management"]
        MIX["⚡ Mixed-Signal<br/>Interfaces"]
        SENS["📊 Sensors &<br/>Actuators"]
    end

    subgraph power["Power Sources"]
        BAT["🔋 Battery<br/>1000mAh"]
        SOL["☀️ Solar<br/>Panel"]
    end

    ANT <--> MCU
    MCU <--> MEM
    MCU <--> MIX
    MIX <--> SENS
    PWR --> ANT
    PWR --> MCU
    PWR --> MEM
    PWR --> MIX
    BAT --> PWR
    SOL --> PWR

    style ANT fill:#E67E22,stroke:#2C3E50,color:#fff
    style MCU fill:#2C3E50,stroke:#16A085,color:#fff
    style MEM fill:#7F8C8D,stroke:#2C3E50,color:#fff
    style PWR fill:#16A085,stroke:#2C3E50,color:#fff
    style MIX fill:#E67E22,stroke:#2C3E50,color:#fff
    style SENS fill:#16A085,stroke:#2C3E50,color:#fff
    style BAT fill:#16A085,stroke:#2C3E50,color:#fff
    style SOL fill:#E67E22,stroke:#2C3E50,color:#fff

Figure 594.8: Generic IoT device block diagram showing six major subsystems: Wireless Transceiver (antenna, RF front-end), Energy Management (battery, solar pane…

Subsystem Functions:

Subsystem Function Power Consumption Example Components
Wireless Transceiver RF communication 10-100mA (TX), 5-20mA (RX) ESP32 Wi-Fi, SX1276 LoRa, nRF52 BLE
Microcontroller Program execution, logic 1-50mA (active), 1-50µA (sleep) ARM Cortex-M0/M4, ESP32, ATmega
Memory Code and data storage Included in MCU Flash (program), SRAM (data)
Energy Management Voltage regulation, charging 1-10µA overhead LDO, DC-DC converter, PMIC
Mixed-Signal ADC, DAC, comparators 10-100µA per channel Built into MCU or external ICs
Sensors/Actuators Physical world interface 1µA - 100mA (varies widely) BME280, DHT22, motors, LEDs

Real Numbers - Ultra-Low-Power Design:

With a 1000mAh battery and 11.4µA average sleep current: - Battery Life = 1000mAh / 0.0114mA = 87,719 hours = 10 years

This is achievable when: - Sleep mode 99.9% of time - Wake briefly (100ms) every 15 minutes - Transmit data once per hour

594.1.4 Material Classification

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graph LR
    subgraph COND["Conductors"]
        C1["Free Electrons<br/>Low Resistance<br/>~10⁻⁸ Ω·m"]
        C2["Copper, Gold<br/>Aluminum"]
    end

    subgraph SEMI["Semiconductors"]
        S1["Controllable<br/>Medium Resistance<br/>Variable"]
        S2["Silicon, Germanium<br/>Gallium Arsenide"]
    end

    subgraph INSU["Insulators"]
        I1["Bound Electrons<br/>High Resistance<br/>~10¹⁵ Ω·m"]
        I2["Rubber, Glass<br/>Plastic"]
    end

    COND -.Increasing Resistance.-> SEMI
    SEMI -.Increasing Resistance.-> INSU

    style COND fill:#16A085,stroke:#138D75,color:#fff
    style SEMI fill:#E67E22,stroke:#D35400,color:#fff
    style INSU fill:#7F8C8D,stroke:#5D6D7E,color:#fff
    style C1 fill:#ECF0F1,stroke:#16A085,color:#2C3E50
    style C2 fill:#ECF0F1,stroke:#16A085,color:#2C3E50
    style S1 fill:#ECF0F1,stroke:#E67E22,color:#2C3E50
    style S2 fill:#ECF0F1,stroke:#E67E22,color:#2C3E50
    style I1 fill:#ECF0F1,stroke:#7F8C8D,color:#2C3E50
    style I2 fill:#ECF0F1,stroke:#7F8C8D,color:#2C3E50

Figure 594.9: Material Conductivity Classification: Conductors, Semiconductors, and Insulators 

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flowchart TB
    subgraph device["IoT SENSOR NODE"]
        subgraph conductors["CONDUCTORS (Carry current)"]
            C1["PCB Copper Traces<br/>Connect components"]
            C2["Wire Leads<br/>External connections"]
            C3["Solder Joints<br/>Component mounting"]
        end

        subgraph semiconductors["SEMICONDUCTORS (Control current)"]
            S1["ESP32 Chip<br/>Millions of transistors"]
            S2["Sensor IC<br/>Signal processing"]
            S3["Voltage Regulator<br/>Power control"]
        end

        subgraph insulators["INSULATORS (Block current)"]
            I1["PCB Substrate (FR4)<br/>Isolates traces"]
            I2["Plastic Enclosure<br/>Safety barrier"]
            I3["Conformal Coating<br/>Moisture protection"]
        end
    end

    conductors --> semiconductors
    semiconductors --> insulators

    style conductors fill:#E8F5E9,stroke:#16A085
    style semiconductors fill:#FFF3E0,stroke:#E67E22
    style insulators fill:#E3F2FD,stroke:#2C3E50

Figure 594.10: Device anatomy view: Every IoT device uses all three material types. CONDUCTORS (copper traces, wires) carry current between components. SEMICONDUCTORS (chips, ICs) actively control and process signals. INSULATORS (FR4 board, plastic case) prevent unwanted current flow and provide safety. Understanding materials helps with troubleshooting: broken trace? Replace conductor. Chip not working? Semiconductor issue. Short circuit? Insulator failure.

{fig-alt=“Electronics diagram illustrating”Conductors”, “Free Electrons Low Resistance ~10⁻⁸ Ω·m”, “Copper, Gold Aluminum” showing semiconductor components, transistor circuits, diode operation, signal amplification, or switching circuits used in sensor and actuator interfacing for IoT systems.”}

Type Electron Mobility Resistance Examples IoT Use
Conductor Free to move Very low (~10-8 Ω·m) Copper, gold, aluminum Wires, PCB traces, contacts
Insulator Cannot move Very high (~1015 Ω·m) Rubber, glass, plastic Cable insulation, PCB substrate
Semiconductor Conditionally mobile Medium (variable) Silicon, germanium Transistors, diodes, ICs
Diagram showing three material classes based on electrical conductivity: insulators with tightly bound electrons and high resistance, conductors with free electrons and low resistance, and semiconductors with controllable conductivity between the two extremes
Figure 594.11: Classification of materials: insulators, conductors, and semiconductors
Educational diagram reviewing semiconductor fundamentals: doping process creating N-type and P-type materials, energy band diagrams, and charge carrier mobility concepts
Figure 594.12: Semiconductor knowledge check and key concepts

594.1.5 The Semiconductor Advantage

Key Property: Semiconductors can be switched between conducting and insulating states by applying external energy (voltage or current).

This controllability makes ALL modern electronics possible.

594.2 What’s Next?

Continue to Semiconductors and Doping to learn about N-type and P-type semiconductors, diodes, and PN junctions.