12 Conductors, Insulators, Semiconductors

electronics

conductors

insulators

12.1 Start Simple

Imagine touching a probe to copper, plastic, and silicon on the same board. Copper carries charge easily, plastic blocks it, and silicon can be controlled so it sometimes acts like either one. Start by asking which material should conduct, which should isolate, and what temperature, voltage, or doping changes that answer.

12.2 Learning Objectives

Classify materials as conductors, insulators, or semiconductors based on their electrical properties and explain why semiconductors are essential to IoT electronics
Identify passive and active electronic components and describe their roles in common IoT circuit patterns
Select appropriate resistors, capacitors, and transistors for IoT applications using datasheet specifications and rating guidelines
Design basic IoT interface circuits including voltage dividers, pull-up resistors, current-limiting circuits, and decoupling networks

In 60 Seconds

All materials fall into three categories based on electrical conductivity: conductors (copper wires), insulators (plastic casings), and semiconductors (silicon chips). Semiconductors are the foundation of all IoT electronics because their conductivity can be controlled, enabling transistors, diodes, and integrated circuits.

12.3 Why This Chapter Matters

Students often want to skip material classification because it looks too basic, but this chapter is what makes later component choices understandable instead of arbitrary.
Real IoT design depends on knowing why copper is used for traces, why plastic and solder mask isolate circuits, and why silicon can become a controllable switch instead of just another material.
This chapter also introduces the component families you will repeatedly meet on schematics, breakout boards, and datasheets.

12.4 How To Use This Chapter

On a first pass, focus on three questions: what carries current easily, what blocks it, and what can be controlled.
Use the taxonomy and quick-reference sections as a map of the parts ecosystem, not as something to memorize line by line.
If you are handling real boards while reading, stop and identify examples of passive components, active components, and integrated circuits around you.

Chapter Roadmap

This chapter is broad, so use this route through it:

First classify the parts you see on a board: passive components, active components, and integrated circuits.
Then practice the common component calculations – LED resistors, voltage dividers, RC timing, and decoupling values.
Next zoom out to the IoT device architecture that connects wireless, power, compute, memory, mixed-signal, and sensor blocks.
Finally return to materials: conductors carry current, insulators isolate nodes, and semiconductors make controlled switching possible.

Checkpoints recap the design rules as you go, and anything titled “Deep dive” is optional on a first read.

12.5 Conductors and Semiconductors

~15 min | Foundational | P06.C05.U01

Materials behave differently when it comes to conducting electricity. Before exploring material properties, let’s first understand how electronic components are classified in IoT systems.

Start with the parts ecosystem. If you can tell which parts only store or dissipate energy and which parts control current, the later material categories will feel less abstract.

12.5.1 Electronic Components Taxonomy

Electronic components taxonomy diagram showing passive components (resistors, capacitors, inductors) that cannot amplify signals, active components (diodes, transistors, thyristors) that can control and amplify current, and integrated circuits combining components into sensors, microcontrollers, and wireless modules — Electronic components taxonomy

Passive RCL Reference

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)

Component Quick Reference

12.5.2 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

Deep dive: Putting Numbers to It

RC time constant determines how fast a capacitor charges through a resistor – critical for debouncing buttons and timing circuits:

\[\tau = R \times C\]

Example: Button debounce circuit with 10kΩ pull-up and 100nF capacitor:

\[\tau = 10,000\Omega \times 0.0000001F = 0.001s = 1ms\]

The capacitor charges to 63% of final voltage in 1ms, effectively filtering mechanical switch bounce (<10ms typical).

After 5τ (5ms), voltage reaches 99.3% of final value – eliminating false triggers.

LC resonant frequency determines antenna and RF filter design:

\[f = \frac{1}{2\pi\sqrt{LC}}\]

Example: 433 MHz LoRa antenna matching network:

\[f = 433 \times 10^6 \text{ Hz}\]

\[LC = \frac{1}{(2\pi f)^2} = \frac{1}{(2\pi \times 433 \times 10^6)^2} = 1.35 \times 10^{-19}\]

Using L = 10nH: $C = \frac{1.35 \times 10^{-19}}{10 \times 10^{-9}} = 13.5pF$ ← typical antenna tuning capacitor value.

12.5.3 IoT Component Reference

A practical reference for selecting and using electronic components in IoT projects, with specifications and real-world use cases. Consider a typical IoT sensor module like the ultrasonic distance sensor below – it combines passive components (resistors, capacitors for signal conditioning), active components (transistors, op-amps for amplification), and an integrated circuit for digital output.

Ultrasonic sensor module showing transducer elements, signal conditioning circuitry, and connection interface commonly used in IoT distance measurement applications — Figure 12.2: Ultrasonic sensor module used in IoT distance measurement and proximity detection

12.5.3.1 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

12.5.3.2 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	Low power; MCP6002 is rail-to-rail
Voltage Regulator (Linear)	Stable DC voltage	3.3V/5V from battery	AMS1117, LM7805	Dropout: 1.0-2.0V, 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
Linear vs Switching Regulator: Linear for low noise (<100mA), Switching for efficiency (>100mA)

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 12.3: 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 12.4: 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 12.5: 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 12.6: 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 12.7: 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.

12.5.3.3 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)

12.5.3.4 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

12.5.3.5 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=0.06W → use 1/8W (0.125W) 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:

Wrong: “Any resistor will work.” Fix: calculate exact value and power rating.
Wrong: using a 5V sensor with a 3.3V ADC directly. Fix: add a voltage divider or level shifter.
Wrong: connecting a motor directly to GPIO. Fix: use a transistor/MOSFET switch.
Wrong: forgetting the flyback diode on a relay. Fix: add a 1N4007 across the coil.
Wrong: no decoupling capacitor on an MCU. Fix: add 100nF at each Vcc pin.

12.5.3.6 Quick Component Calculations

LED Current Limiting:

Step	Calculation
Given	ESP32 GPIO = 3.3V, red LED Vf = 2.0V, desired current = 10mA
Resistor	R = (Vsupply - Vf) / I = (3.3 - 2.0) / 0.010 = 130Ω
Standard value	Use 150Ω
Power	P = I² × R = (0.01)² × 150 = 0.015W, so a 1/8W resistor is sufficient

Voltage Divider for 5V→3.3V:

Step	Calculation
Given	5V sensor output, 3.3V maximum ADC input
Formula	Vout = Vin × (R2 / (R1 + R2))
Target	3.3 = 5 × (R2 / (R1 + R2))
Choose values	R2 = 10kΩ, R1 = 5.15kΩ, use 5.1kΩ standard value
Verify	5 × (10k / (5.1k + 10k)) = 3.31V

Decoupling Capacitor Value:

Step	Calculation
Rule of thumb	C = I × t / ΔV
Example	MCU draws 100mA for a 10ns switching transient, allow 0.1V droop
Result	C = 0.1 × 10×10⁻⁹ / 0.1 = 10nF
Practical choice	Use 100nF for safety margin

Checkpoint: Component Calculations

You now know:

A 10kΩ pull-up with a 100nF capacitor gives a 1ms time constant, and 5τ reaches 99.3% after 5ms.
The 5V to 3.3V divider example uses 10kΩ and 5.1kΩ and verifies about 3.31V.
The LED example chooses 150Ω and dissipates 0.015W, so a 1/8W resistor is sufficient.

12.5.3.7 Interactive Component Calculators

Use the sliders below to calculate LED resistor values, voltage divider outputs, and RC time constants in real time.

LED Current-Limiting Resistor Calculator:

Show code

viewof v_supply = Inputs.range([1.8, 12], {value: 3.3, step: 0.1, label: "Supply voltage (V)"})
viewof v_fwd = Inputs.range([1.0, 3.6], {value: 2.0, step: 0.1, label: "LED forward voltage (V)"})
viewof i_led = Inputs.range([1, 30], {value: 10, step: 1, label: "Desired LED current (mA)"})

Show code

{
  const valid = v_supply > v_fwd;
  const r_exact = valid ? (v_supply - v_fwd) / (i_led / 1000) : 0;
  const e12 = [10,12,15,18,22,27,33,39,47,56,68,82];
  function nearestE12(val) {
    if (val <= 0) return 0;
    let decade = 1;
    while (e12[e12.length-1] * decade < val) decade *= 10;
    while (e12[0] * decade > val) decade /= 10;
    let best = e12[0] * decade;
    for (const v of e12) {
      for (const d of [decade, decade*10]) {
        if (Math.abs(v*d - val) < Math.abs(best - val)) best = v*d;
      }
    }
    return best;
  }
  const r_std = nearestE12(r_exact);
  const i_actual = r_std > 0 ? ((v_supply - v_fwd) / r_std * 1000) : 0;
  const p_resistor = (i_actual/1000) * (i_actual/1000) * r_std;
  return html`<div style="background:#f0f7f4; border-left:4px solid #16A085; padding:12px; border-radius:4px; font-family:Arial,sans-serif;">
    <b>R<sub>exact</sub></b> = (${v_supply}V - ${v_fwd}V) / ${i_led}mA = <b>${valid ? r_exact.toFixed(1) : "---"} &Omega;</b><br>
    <b>Nearest E12 standard value</b>: <b>${valid ? r_std : "---"} &Omega;</b><br>
    <b>Actual current with ${valid ? r_std : "---"}&Omega;</b>: ${valid ? i_actual.toFixed(2) : "---"} mA<br>
    <b>Power dissipated in resistor</b>: ${valid ? (p_resistor*1000).toFixed(1) : "---"} mW ${valid && p_resistor < 0.125 ? "(use 1/8W)" : valid && p_resistor < 0.25 ? "(use 1/4W)" : valid ? "(use 1/2W)" : ""}<br>
    ${!valid ? "<em style='color:#E74C3C;'>Supply voltage must exceed LED forward voltage.</em>" : ""}
  </div>`;
}

Voltage Divider Calculator:

Show code

viewof v_in = Inputs.range([1, 24], {value: 5, step: 0.1, label: "Input voltage (V)"})
viewof r1_kohm = Inputs.range([0.1, 100], {value: 5.1, step: 0.1, label: "R1 - top resistor (k\u03A9)"})
viewof r2_kohm = Inputs.range([0.1, 100], {value: 10, step: 0.1, label: "R2 - bottom resistor (k\u03A9)"})

Show code

{
  const v_out = v_in * (r2_kohm / (r1_kohm + r2_kohm));
  const i_div = v_in / ((r1_kohm + r2_kohm) * 1000);
  const p_total = v_in * i_div;
  const safe33 = v_out <= 3.3;
  return html`<div style="background:#f0f4f7; border-left:4px solid #3498DB; padding:12px; border-radius:4px; font-family:Arial,sans-serif;">
    <b>V<sub>out</sub></b> = ${v_in}V &times; (${r2_kohm}k&Omega; / (${r1_kohm}k&Omega; + ${r2_kohm}k&Omega;)) = <b>${v_out.toFixed(3)} V</b><br>
    <b>Divider current</b>: ${(i_div * 1000).toFixed(3)} mA<br>
    <b>Power dissipated</b>: ${(p_total * 1000).toFixed(2)} mW<br>
    ${safe33 ? "<span style='color:#16A085;'>&#10003; Safe for 3.3V ADC input</span>" : "<span style='color:#E74C3C;'>&#10007; Exceeds 3.3V - not safe for 3.3V ADC</span>"}
  </div>`;
}

RC Time Constant Calculator:

Show code

{
  const tau_ms = rc_r * rc_c / 1000;
  const t63 = tau_ms;
  const t99 = tau_ms * 5;
  const fc = 1 / (2 * Math.PI * (rc_r * 1000) * (rc_c * 1e-9));
  return html`<div style="background:#f7f4f0; border-left:4px solid #E67E22; padding:12px; border-radius:4px; font-family:Arial,sans-serif;">
    <b>&tau;</b> = ${rc_r}k&Omega; &times; ${rc_c}nF = <b>${tau_ms < 1 ? (tau_ms * 1000).toFixed(1) + " &mu;s" : tau_ms.toFixed(3) + " ms"}</b><br>
    <b>63% charge time (1&tau;)</b>: ${tau_ms < 1 ? (t63 * 1000).toFixed(1) + " &mu;s" : t63.toFixed(3) + " ms"}<br>
    <b>99.3% charge time (5&tau;)</b>: ${t99 < 1 ? (t99 * 1000).toFixed(1) + " &mu;s" : t99.toFixed(3) + " ms"}<br>
    <b>RC low-pass cutoff frequency</b>: ${fc > 1e6 ? (fc / 1e6).toFixed(2) + " MHz" : fc > 1e3 ? (fc / 1e3).toFixed(2) + " kHz" : fc.toFixed(2) + " Hz"}<br>
    ${t99 >= 5 && t99 <= 50 ? "<span style='color:#16A085;'>&#10003; Good range for button debouncing (5-50ms)</span>" : t99 < 5 ? "<span style='color:#7F8C8D;'>Fast settling - suitable for signal filtering</span>" : "<span style='color:#7F8C8D;'>Slow settling - suitable for timing circuits</span>"}
  </div>`;
}

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	Low-power op-amp	LM358 (general), MCP6002 (rail-to-rail)	Single supply compatible
5V↔︎3.3V bidirectional	Logic level shifter IC	TXS0108E, BSS138	I2C, SPI safe conversion

Pro Tips for Component Selection:

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

Generic IoT Device Architecture

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

Figure 12.8: Generic IoT device block diagram showing six major subsystems: Wireless Transceiver, Energy Management, Microcontroller, Memory, Mixed-Signal, and Sensors/Actuators

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

Checkpoint: Architecture and Power

You now know:

A typical IoT device combines wireless, energy management, microcontroller, memory, mixed-signal, and sensor or actuator subsystems.
Active currents can sit around 1-50mA for the microcontroller and 10-100mA for wireless transmit, while sleep currents can fall to microamp levels.
With a 1000mAh battery and 11.4µA average sleep current, the chapter’s calculation gives 87,719 hours, about 10 years.

Now move from whole-device blocks to the materials underneath them. The same device only works because copper, FR4, plastic, and silicon each play a different electrical role.

12.5.4 Material Classification

Now that we have surveyed the electronic components used in IoT systems, let’s examine the underlying material science that makes them possible. All materials fall into three categories based on how freely their electrons can move.

Semiconductor band gap diagram comparing conductors, semiconductors, and insulators — Figure 12.9: Material Conductivity Classification: Conductors, Semiconductors, and Insulators

IoT device anatomy showing how conductors (copper traces and wires) carry current between components, semiconductors (silicon chips and ICs) control and process signals, and insulators (FR4 board substrate and plastic casing) prevent unwanted current flow and provide safety — Figure 12.10: 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.

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 12.11: 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 12.12: Semiconductor knowledge check and key concepts

Checkpoint: Materials

You now know:

Conductors such as copper have very low resistivity, around 10^-8 Ω·m, and carry current in traces, wires, and contacts.
Insulators such as rubber, glass, and plastic have very high resistance, around 10^15 Ω·m in the chapter table, and protect against unwanted current paths.
FR4 appears later with about 10^12 ohm per square surface resistance, which is why contamination and moisture matter on high-impedance circuits.

12.6 Phoebe’s Field Notes: Why Materials Turn Into Circuit Numbers

Phoebe the physics guide

Phoebe’s Why

The material table and the circuit recipes are the same physics seen at two scales. A conductor has many mobile charges, so a small electric field produces useful current. An insulator has almost no mobile charges, so the same field produces negligible current. A semiconductor sits between them because voltage, light, heat, or doping can change how many carriers are available. Once the material sets the resistance or capacitance, the circuit equations decide the IoT behavior: current limiting, divider scaling, RC settling, and leakage margins are all charge motion plus stored electric field.

The Derivation

Start with the definitions of voltage and current:

\[V = \frac{W}{Q}\]

\[I = \frac{\Delta Q}{\Delta t}\]

For an ohmic material, resistance is the voltage needed per ampere of charge flow:

\[R = \frac{V}{I}\]

Geometry converts material resistivity into circuit resistance:

\[R = \rho\frac{L}{A}\]

Two resistors in series carry the same current, so the bottom resistor sees the fraction of the input voltage proportional to its resistance:

\[V_{\mathrm{out}} = V_{\mathrm{in}}\frac{R_2}{R_1 + R_2}\]

A capacitor stores charge according to $Q = CV$. Charging it through a resistor gives the first-order response

\[\tau = RC\]

and the equivalent low-pass cutoff is

\[f_c = \frac{1}{2\pi RC}\]

For a semiconductor, the material knob is carrier density:

\[\sigma = q(n\mu_n + p\mu_p)\]

\[\rho = \frac{1}{\sigma}\]

Doping or gate voltage changes $n$ and $p$, so silicon can behave like a controllable resistor, diode, or switch instead of a fixed conductor.

Worked Numbers: This Chapter’s Parts

LED limiter: the GPIO provides $3.3 - 2.0 = 1.30$ V across the resistor. At the target $10.0$ mA, $R = 1.30/0.0100 = 130\Omega$. The chapter’s $150\Omega$ standard value gives actual current $(3.3 - 2.0)/150 = 8.67$ mA; the design-current power check is $(0.0100)^2 \times 150 = 0.0150$ W.
5 V to 3.3 V divider: with $R_1 = 5.1$ k$\Omega$ and $R_2 = 10$ k$\Omega$, $V_{\mathrm{out}} = 5.00(10/(5.1+10)) = 3.31$ V. Divider current is $5.00/15.1$ k$\Omega = 0.331$ mA.
Button RC filter: $10$ k$\Omega \times 100$ nF $= 1.00$ ms, so $5\tau = 5.00$ ms and $f_c = 1/(2\pi \times 0.00100) = 159$ Hz. That is why short switch bounce is smoothed while slow button presses still pass.
Decoupling pulse: a $100$ mA, $10$ ns current spike with only $0.1$ V droop needs $C = It/\Delta V = 0.1 \times 10^{-8}/0.1 = 10.0$ nF; choosing $100$ nF adds a $10.0\times$ margin.
Material contrast: the table’s $10^{-8}\Omega\cdot\mathrm{m}$ conductor and $10^{15}\Omega\cdot\mathrm{m}$ insulator differ by $10^{23}\times$ for the same geometry, while FR4 at about $10^{12}\Omega$ per square is why moisture and flux residue matter on high-impedance ADC nodes.

12.6.1 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.

Knowledge Check: Decoupling Capacitors

For Kids: Meet the Sensor Squad!

The Sensor Squad discovers why materials matter!

Sammy the Sensor was curious about something. “Max, why are some things made of copper and other things made of plastic?” Max the Microcontroller loved this question!

“Imagine a hallway full of kids,” Max explained. “In a CONDUCTOR like copper, all the kids can move freely – they’re like electrons zooming through the hallway. That’s why copper wires carry electricity so well!” Lila the LED nodded. “That’s how electricity gets to me!”

“Now imagine a hallway where all the kids are stuck to their desks and can’t move at all,” Max continued. “That’s an INSULATOR like rubber or plastic. No electrons can flow, so no electricity gets through. That’s why your charging cable has a plastic coating – it keeps the electricity inside the wire and protects your fingers!”

“But here’s the really cool part,” said Max, getting excited. “A SEMICONDUCTOR like silicon is a hallway where the kids are sitting at their desks, but if someone gives them a push – like adding a little bit of special material called a dopant – some of them can start moving! It’s like a teacher saying ‘OK, you can get up now!’”

Bella the Battery was amazed. “So semiconductors can be switched between ‘conducting’ and ‘not conducting’?” “Exactly!” said Max. “That’s what makes transistors work – tiny switches that can turn on and off billions of times per second. That’s how I think and make decisions!”

Sammy looked at the circuit board. “So the copper traces are conductors, the green board is an insulator, and all those tiny chips are semiconductors?” “You got it!” cheered the whole Sensor Squad. “Every IoT device uses all three materials working together!”

12.6.2 Key Words for Kids

Word	What It Means
Conductor	A material that lets electricity flow easily (like copper wire)
Insulator	A material that blocks electricity (like rubber or plastic)
Semiconductor	A material that can switch between conducting and blocking electricity
Silicon	The most common semiconductor material, found in every computer chip
Doping	Adding special ingredients to silicon to control how it conducts electricity
Circuit Board	The green board inside electronics where copper conductors connect all the chips

Capacitor Type Selection

Context: You need to add capacitors to your IoT circuit. Choosing the wrong type can cause circuit failure, noise issues, or premature component failure. Use this framework to select the optimal capacitor for each application.

Capacitor Type	Capacitance Range	Key Properties	Typical Applications	Cost	Pitfalls
Ceramic (MLCC)	1pF - 100µF	Low ESR, high frequency response, temperature-stable (X7R), small size	Decoupling, bypassing, high-frequency filtering	Low ($0.05-$0.50)	Voltage coefficient (capacitance drops at rated voltage), microphonic (vibration sensitivity)
Electrolytic (Aluminum)	1µF - 10,000µF	High capacitance, polarized (must observe polarity), high ESR	Bulk power supply filtering, energy storage	Low ($0.10-$1)	Limited lifespan (2000-10,000 hrs), fails open/short, temperature-sensitive
Tantalum	0.1µF - 1000µF	Stable, low leakage, polarized, lower ESR than aluminum	Power supply filtering where size matters, audio circuits	Medium ($0.50-$3)	Catastrophic failure mode (burns/explodes if reversed), surge-sensitive
Film (Polyester/Polypropylene)	1nF - 10µF	Low loss, non-polarized, stable over temperature	Timing circuits, signal coupling, precision filters	Medium ($0.20-$2)	Large physical size limits use in compact IoT devices

Decision Guide:

Application	Recommended Capacitor	What to Check
Decoupling MCU/IC power pins	100nF X7R or X5R ceramic MLCC	Place within 5mm of the power pin; add 10µF ceramic for local bulk storage
Power supply bulk storage	100µF-1000µF electrolytic	Place in parallel with 100nF ceramic; check ESR, ripple current, and lifetime
ADC reference filtering	1-10µF polypropylene film, or high-quality X7R ceramic	Check voltage coefficient and noise requirements
Precision timing circuit	Film capacitor, or C0G/NP0 ceramic for best stability	Check tolerance and temperature coefficient
Energy storage	1000µF+ electrolytic, or supercapacitor for very high values	Consider series resistance and leakage current

Critical Selection Criteria:

1. Voltage Rating:

Rule: Always use ≥2× operating voltage
Example: 5V circuit → use 10V-rated minimum (16V for margin)
Why: Capacitance drops near rated voltage (ceramic), lifetime extends with derating

2. Temperature Coefficient:

C0G/NP0: ±30ppm/°C (best stability, small values)
X7R: ±15% over -55°C to +125°C (good stability, larger values)
Y5V: +22% to -82% over -30°C to +85°C (worst, avoid for critical circuits)
Choose: X7R minimum for IoT (C0G for precision timing)

3. ESR (Equivalent Series Resistance):

Low ESR needed: Decoupling (ceramic), switching regulators
High ESR OK: Bulk filtering with aluminum electrolytics
Check datasheet: For >100mA ripple current, verify ESR won’t cause excessive heating

4. Physical Size:

0805 ceramic: 2mm × 1.25mm (hand-solderable, common values)
1206 ceramic: 3.2mm × 1.6mm (easier for beginners)
Electrolytic radial: 5-10mm diameter (through-hole, large values)
Design tip: Reserve space on PCB BEFORE finalizing component selection

Worked Example: ESP32 Power Supply Design

Requirements:

Input: 5V USB
Output: 3.3V @ 500mA max (ESP32 + peripherals)
LDO regulator: AMS1117-3.3

Capacitor selection:

1. Input decoupling (5V rail):

C1: 100nF X7R ceramic (high frequency noise)
- Voltage: 10V rating (2× safety margin)
- Package: 0805
C2: 10µF X7R ceramic (bulk storage near regulator)
- Voltage: 10V rating
- Package: 1206 (larger for higher capacitance)

2. Output decoupling (3.3V rail):

C3: 100nF X7R ceramic (high frequency)
- Voltage: 6.3V rating
- Package: 0805
C4: 10µF X7R ceramic (bulk storage)
- Voltage: 6.3V rating
- Package: 1206
C5: 100µF aluminum electrolytic (large transient currents)
- Voltage: 6.3V rating minimum
- Low ESR type (<100mΩ) for 500mA load switching

3. ESP32 VCC pins (near chip):

C6-C9: 100nF X7R ceramic (one per VCC pin)
- Voltage: 6.3V rating
- Package: 0805
- Critical: Place within 5mm of each VCC pin

Why this combination?

Ceramic caps handle MHz-GHz switching noise from ESP32 digital logic
Electrolytic cap provides energy reservoir for Wi-Fi TX bursts (200mA for 1-2s)
Multiple 100nF caps (one per power pin) minimize inductance
Cost: ~$1 total for all capacitors

Common Mistakes to Avoid:

Wrong: using Y5V ceramic for power supply filtering. Capacitance can drop 80% with temperature and voltage.
Wrong: forgetting voltage derating. Electrolytic capacitors fail early when run at their rated voltage.
Wrong: reversing electrolytic or tantalum polarity. This creates an explosion and fire hazard.
Wrong: using one large capacitor instead of multiple small capacitors. High inductance hurts high-frequency response.
Wrong: ignoring ESR for high ripple current. The capacitor overheats and fails.
Wrong: omitting the bulk capacitor on a switching regulator output. The output voltage can become unstable.

Quick Reference Card:

Need	Use This	Value	Voltage	Notes
MCU decoupling	Ceramic X7R	100nF	2× Vcc	One per VCC pin
Bulk power	Electrolytic	100-1000µF	2× Vcc	Low ESR type
ADC reference	Ceramic C0G or Film	1-10µF	2× Vref	Ultra-low noise
Timing (RC)	Ceramic C0G or Film	Per calculation	2× Vmax	Stable over temp
Energy storage	Electrolytic or Supercap	>1000µF	2× Vcc	Check leakage current

Default Recommendation: For general IoT power supply decoupling, use 100nF ceramic (X7R, 0805) + 10µF ceramic (X7R, 1206) + 100µF electrolytic (low ESR) in parallel. This combination handles high-frequency noise, moderate transients, and large current bursts – covering 90% of IoT applications.

Passive vs Active Components

The big picture: Electronic components fall into two categories based on energy behavior: passive components (resistors, capacitors, inductors) can only consume or store energy, while active components (transistors, diodes, ICs) can control current flow and amplify signals by using external power.

Step-by-step breakdown:

Resistors: Convert electrical energy to heat following P = I²R - Real example: 220Ω resistor limiting 15mA LED current dissipates P = (0.015)² × 220 = 0.05W as heat, well within its 0.25W power rating and staying cool to touch
Capacitors: Store energy in electric field (E = ½CV²), releasing it during voltage dips to stabilize power supplies - Real example: 100µF capacitor at 5V stores 1.25mJ, supplementing the regulator output during brief ESP32 Wi-Fi transmission current spikes (~200mA bursts lasting 1-2ms)
Transistors: Use small control signal to switch or amplify large currents - Real example: A 3.3V GPIO driving an NPN BJT base through a 1kΩ resistor (Ib = (3.3V - 0.7V) / 1kΩ = 2.6mA base current, 8.6mW input power) controls a 12V motor at 200mA collector current (2.4W output power), providing roughly 280x power gain. MOSFETs achieve even higher ratios since their gate draws near-zero DC current

Why this matters: Passive components set voltage/current levels and filter noise, while active components make decisions and drive loads. Every IoT circuit combines both: passives condition signals, actives process and amplify them.

You have now seen the chapter at three scales: individual parts, device subsystems, and material classes. The remaining sections connect those ideas to the surrounding electronics module and give you review tasks to check whether the distinctions hold.

12.7 Concept Relationships

This chapter connects to other IoT electronics topics:

Related Concept	Chapter Link	Relationship
Semiconductors	Semiconductors and Doping	N-type and P-type materials enable transistors
Circuit Analysis	Electricity Fundamentals	Ohm’s law applies to resistors, capacitors add impedance
Sensor Interfaces	Sensor Circuits	Resistor dividers and capacitor filters condition sensor signals
Power Supply	Power Management	Capacitors smooth voltage, inductors store energy in DC-DC converters

12.8 Try It Yourself

Challenge: Build a Visual Resistor Color Code Decoder

Objective: Create a physical reference tool to quickly identify resistor values without looking up tables.

Materials Needed:

Index card or cardboard (10cm × 15cm)
Colored markers or pencils (10 colors: black, brown, red, orange, yellow, green, blue, violet, gray, white)
Ruler and pen

Steps:

Draw 4 colored bands on the card representing a resistor
Create a color-to-digit reference: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, White=9
Write multiplier column: Gold=×0.1, Black=×1, Brown=×10, Red=×100, Orange=×1k, Yellow=×10k, Green=×100k, Blue=×1M
Add tolerance row: Gold=±5%, Silver=±10%, None=±20%
Practice decoding: Brown-Black-Red-Gold = 10 × 100Ω ± 5% = 1kΩ

Solution Examples:

Yellow-Violet-Orange-Gold = 47 × 1000Ω ± 5% = 47kΩ (common pull-up resistor)
Brown-Black-Brown-Gold = 10 × 10Ω ± 5% = 100Ω (common gate resistor)
Red-Red-Red-Gold = 22 × 100Ω ± 5% = 2.2kΩ (common current limiting)

Expected Observation: After decoding 10-15 resistors, you’ll memorize common values and recognize patterns instantly. Most IoT circuits use E12 series values (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82).

Key Takeaway

Every IoT device uses all three material types: conductors (copper traces and wires) carry current between components, semiconductors (chips and ICs) actively control and process signals, and insulators (board substrate and casings) prevent unwanted current flow. Understanding this classification is the first step toward designing reliable electronic circuits.

12.9 See Also

Component Selection Resources:

Transistor Selection Guide - Choose the right switching device
Capacitor Types Decision Framework - When to use ceramic vs electrolytic
Power Dissipation Calculations - Calculate resistor wattage ratings

Circuit Design Patterns:

Voltage Dividers - Resistive signal conditioning
Decoupling Capacitors - Power supply noise filtering
Pull-up/Pull-down Resistors - Define logic levels

12.10 Review: Match the Concepts

12.11 Review: Put It in Order

Common Pitfalls

PCB Substrate Insulation Limits

FR4 PCB substrate has a surface resistance of approximately 10^12 ohm per square — high enough to be treated as insulating for normal circuits. However, moisture absorption, flux residue, and PCB contamination can drop surface resistance to megaohm or kilohm levels on high-impedance circuits (ADC inputs, electrometers). Always clean PCB flux residue and use conformal coating in humid environments.

Conductor vs Insulation Rating

A wire rated for 10 A continuous current refers to the conductor’s heating limit, not the insulation’s voltage limit. The same wire may have insulation rated for only 300 V. Using 10 A rated wire in a 240 V AC circuit without verifying the insulation voltage rating can result in insulation breakdown and short circuits.

Wire Gauge for Actuators

Resistance of copper wire increases with length and decreases with cross-section (gauge). AWG 28 signal wire (0.08 mm^2) carrying 2 A for a motor creates a voltage drop of 0.5 V per meter — enough to affect motor performance. Use AWG 22-18 wire for motor power runs and calculate voltage drop for all power wiring longer than 30 cm.

PCB Ground Contact in Enclosure

Metal enclosures provide EMI shielding only if the PCB ground plane is connected to the enclosure at one point. Multiple ground connections between PCB and enclosure create ground loops that can introduce 50/60 Hz noise into sensitive circuits. Connect the PCB ground to the enclosure at exactly one point, and use insulating standoffs elsewhere.

Label the Diagram

12.12 What’s Next?

Now that you can classify materials by conductivity and select the right passive and active components, you are ready to explore how semiconductors are engineered at the atomic level:

Next Chapter	What You Will Learn	Link
Semiconductors and Doping	N-type and P-type materials, PN junctions, diodes, and rectification	Semiconductors and Doping
Transistor Selection Guide	BJT vs MOSFET, logic-level switching, and gate driver circuits	Transistor Selection Guide
Electronics Introduction	Overview of the full electronics module and learning path	Electronics Introduction
Electricity Fundamentals	Voltage, current, resistance, and Ohm’s Law as the basis for all circuit analysis	Electricity Fundamentals
Sensor Circuits and Signals	How resistor dividers, op-amp stages, and filters condition real sensor outputs	Sensor Circuits

Code Challenge

12.13 Floating Inputs and Pull Resistors

The material and component sections above explain why conductors carry current, insulators isolate nodes, and semiconductor gates can sense voltage with extremely little input current. In a real IoT circuit, that high-impedance behavior creates a common review question: is every logic input tied to a defined state when no active driver is present?

For the layered engineering checks, continue to Floating Input and Pull Resistor Contracts. It works through undefined CMOS inputs, pull-up and pull-down sizing, leakage and edge-speed trade-offs, and the shoot-through current that makes floating inputs unreliable and wasteful.

12.14 Summary

This chapter explains how conductors, insulators, and semiconductors differ by resistivity and controllable conductivity. Material choice affects wiring, isolation, leakage, sensing behavior, and the reliability of IoT circuits.