1527 Case Studies and Worked Examples

1527.1 Learning Objectives

By the end of this chapter, you will be able to:

Apply the hardware prototyping framework to real projects
Analyze a complete development journey from concept to production
Work through component selection and power budget calculations
Test your knowledge with comprehensive review quizzes

1527.2 Hardware Prototyping Framework

A complete hardware prototyping framework helps you systematically approach IoT development:

1527.2.1 Platform Selection

Compare platforms based on: - Processing power and memory - Connectivity options (Wi-Fi, BLE, LoRa, cellular) - Power consumption (active, sleep modes) - GPIO availability and interfaces - Development ecosystem and community - Cost and availability

1527.2.2 Component Library

Maintain a catalog of: - Sensors with electrical specifications - Actuators with drive requirements - Communication modules with protocol details - Power components with efficiency data

1527.2.3 Power Budget Analysis

Calculate for each state: - Active current draw - Idle/standby current - Deep sleep current - Estimate battery life based on duty cycles

1527.2.4 Pin Management

Track and validate: - GPIO allocation and conflicts - Voltage level compatibility - Current sourcing/sinking requirements - Shared bus assignments (I2C, SPI)

1527.3 Interactive Simulator: ESP32 IoT Dashboard

ESP32 Multi-Sensor IoT Dashboard

What This Simulates: Complete ESP32 IoT system integrating sensors, Wi-Fi, MQTT, and local display

System Architecture:

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flowchart LR
    DHT[DHT22] --> ESP[ESP32]
    ESP --> OLED[OLED Display]
    ESP --> MQTT[MQTT Broker]
    MQTT --> DB[Database]
    DB --> Dashboard[Web Dashboard]

    style ESP fill:#2C3E50,stroke:#16A085,color:#fff
    style MQTT fill:#16A085,stroke:#2C3E50,color:#fff

How to Use: 1. Click Start Simulation 2. Watch sensors initialize and connect to Wi-Fi 3. See MQTT connection established 4. Observe sensor readings published every 5 seconds

Key Learning Points:

Multi-Sensor Integration - Reading multiple I/O types simultaneously
Wi-Fi Management - Connection handling with reconnection logic
MQTT Publishing - Reliable data transmission to cloud
JSON Formatting - Standard IoT data serialization
Error Handling - Graceful failure recovery

1527.4 Case Study: Smart Thermostat Development

This case study follows a complete development journey from concept to production.

1527.4.1 Project Requirements

Wall-mounted smart thermostat
Temperature and humidity sensing
Occupancy detection (PIR)
Wi-Fi connectivity to cloud
Touchscreen display
2-year target lifespan (with AC power)
FCC/CE certification required
Target retail price: $99

1527.4.2 Phase 1: Proof of Concept (2 months)

Goals: Validate core functionality

Hardware: - ESP32 DevKit - DHT22 sensor (temperature/humidity) - PIR motion sensor - 2.4” TFT display

Key Learnings: - DHT22 too slow (2-second read time) - Display refresh causing Wi-Fi dropouts - Power consumption higher than expected

Iteration 1 Result: Core concept proven, identified technical risks

1527.4.3 Phase 2: Alpha Prototype (3 months)

Improvements: - Replaced DHT22 with SHT31 (faster, more accurate) - Added display buffer to prevent Wi-Fi conflicts - First custom PCB design (2-layer)

PCB Issues Discovered: - Antenna keep-out zone violated (reduced Wi-Fi range) - Power supply noise coupling to ADC - Missing I2C pull-ups

Iteration 2 Result: Functional prototype, 3 PCB respins needed

1527.4.4 Phase 3: Beta Prototype (4 months)

Refinements: - 4-layer PCB with proper ground plane - Switched to ESP32-S3 for improved performance - Added on-device ML for occupancy prediction - Production-intent enclosure design

Testing: - 30-day continuous operation test - Temperature chamber testing (-20C to +60C) - EMC pre-compliance testing

Iteration 3 Result: Production-intent design validated

1527.4.5 Phase 4: Pre-Production (5 months)

Activities: - DFM (Design for Manufacturing) review - Test fixture development - Certification preparation (FCC, CE) - Small batch production (50 units)

Certifications: - FCC Part 15 testing: 2 iterations - CE marking: EMC + safety testing - Total certification cost: $18,000

1527.4.6 Phase 5: Production (2 months)

Final Specifications: - ESP32-S3 (dual-core, Wi-Fi, 8MB flash) - SHT31 (temp/humidity), PIR (occupancy), BH1750 (light) - 3.5” resistive touchscreen - Wi-Fi 802.11n + Bluetooth LE - 24VAC transformer + Li-ion backup - 4-layer PCB, SMT assembly, injection-molded enclosure

Final BOM Cost: $142 at 1000 units Manufacturing Yield: 98.2%

1527.4.7 Timeline Summary

Phase	Duration	PCB Revisions
POC	2 months	0 (breadboard)
Alpha	3 months	3
Beta	4 months	2
Pre-production	5 months	1
Certification	3 months	0
Production	2 months	0
Total	18 months	6 PCB versions

1527.4.8 Key Takeaways

Plan for 3+ PCB iterations - First designs rarely work perfectly
Certification takes time and money - Budget 3 months and $15-20K
Component selection matters - Wrong sensor choice cost 2 months
DFM review is essential - Production issues are expensive
Test in real conditions - Lab success does not equal field success

1527.5 Comprehensive Review Quizzes

1527.5.1 Quiz 1: Platform Selection

Question: You’re at the Proof-of-Concept prototype stage. Which approach is MOST appropriate?

POC is about “Quick validation of concept feasibility.” Breadboarding with dev boards enables rapid iteration to validate ideas cheaply before investing in custom hardware.

Question: Your ESP32 dev board shows 80mA idle current vs 10uA spec. What should you investigate FIRST?

Commercial dev boards include USB-serial converters (CH340: 20mA), voltage regulators (inefficient LDOs: 5-10mA quiescent), power LEDs (5-20mA), which add 30-50mA base consumption. For ultra-low-power, use custom PCBs with only essential components.

1527.5.2 Quiz 2: Component Knowledge

Question: An SMD resistor marked “103” measures what resistance value?

Three-digit SMD code: first two digits are value, third is multiplier (number of zeros). “103” = 10 x 10^3 = 10,000 Ohm = 10k Ohm. Similarly: “104” = 100k Ohm, “473” = 47k Ohm, “220” = 22 Ohm.

Question: Reflow soldering an 0805 capacitor, the solder paste stencil should be what thickness?

Stencil thickness: 0.1-0.15mm (4-6 mil) for fine-pitch, 0.127mm (5 mil) common for standard SMD. For 0805 (2.0mm x 1.25mm), 0.127mm stencil provides adequate paste volume without bridging.

1527.5.3 Quiz 3: Debugging

Question: Your JTAG debugger cannot connect to ARM Cortex-M MCU. Multimeter shows 3.3V on VTREF pin. What should you check NEXT?

VTREF correct means power is good. Most common failures: swapped SWDIO/SWCLK pins, missing pull-up resistors (10k Ohm to 3.3V), wrong pin assignments. SWD requires pull-ups for proper signal levels.

1527.5.4 Quiz 4: PCB Manufacturing

Question: Comparing prototype manufacturing: PCB from OSH Park (USA, $5/sq in, 2-week) vs JLCPCB (China, $2/10pcs, 1-week). When should you choose OSH Park despite higher cost?

OSH Park advantages: USA-based (faster shipping to North America, no customs delays). When 5-day domestic shipping beats 7-14 day international, pay premium. For price-sensitive projects, JLCPCB wins; for urgency, OSH Park shines.

1527.5.5 Quiz 5: Power Design (Multi-Select)

Question: You’re designing a battery-powered environmental sensor PCB. Which THREE design choices will MOST improve power efficiency and battery life?

Options C, D, and F are correct for ultra-low-power design. Low-IQ regulators minimize quiescent current waste. Load switches completely disconnect sensors, eliminating leakage current. MCU deep sleep dominates power budget - 10uA vs 100uA is 10x battery life difference.

1527.6 Knowledge Check: Development Timeline

Show code

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    container.innerHTML = '';
    container.appendChild(InlineKnowledgeCheck.create({
      question: "A startup is planning their hardware development timeline. They want to go from concept to 1000 production units. What is a REALISTIC timeline expectation?",
      options: [
        {text: "3 months - modern tools and fast PCB services enable rapid development", correct: false, feedback: "Overly optimistic. Even with fast PCB turnaround, you need time for breadboard validation, multiple PCB iterations, testing, certification (FCC/CE), and manufacturing setup."},
        {text: "6 months - one PCB revision should be enough with careful design", correct: false, feedback: "Still aggressive. 68% of prototypes need significant PCB redesign. Certification alone takes 8-12 weeks. Budget more time."},
        {text: "12-18 months - allowing for 3-4 prototype iterations, testing, and certification", correct: true, feedback: "Correct! The case study shows 18 months from concept to production. This includes: POC (2mo), Alpha (3mo), Beta (4mo), Pre-production (5mo), Certification (3mo), Manufacturing (2mo). Plan for 2-3 PCB respins."},
        {text: "24+ months - hardware development always takes longer than expected", correct: false, feedback: "While hardware often takes longer than software, 24+ months is excessive for a straightforward IoT product. With good planning and experienced team, 12-18 months is achievable."}
      ],
      difficulty: "medium",
      topic: "prototyping"
    }));
  }
}

1527.7 Summary

Hardware Prototyping Stages: - Proof of Concept (PoC): Core feasibility demonstration - Functional Prototype: Complete feature implementation - Engineering Prototype: Production-intent design - Pre-Production Prototype: Manufacturing validation

Platform Selection: - Microcontrollers (MCUs): Low power, real-time, limited resources - Microprocessors (MPUs): High performance, rich OS, abundant resources - Hybrid approaches: Combined MCU+MPU or System-on-Chip (SoC)

Best Practices: - Start simple, build incrementally - Design for testability with debug headers - Plan for 3+ PCB iterations - Budget time and money for certification - Test in real-world conditions