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Case Study

USB-TTL Converter with BLE Protection & Wireless Terminal​

Tagline: Advanced USB-TTL serial converter with automatic detection, BLE-based protection against USB Killers, and wireless terminal capabilities

Table of Contents​

  1. Executive Summary
  2. Background
  3. Problem Statement
  4. Solution Overview
  5. Technical Approach
  6. Product Features
  7. Benefits
  8. Implementation
  9. Results
  10. Challenges and Learnings
  11. Future Development
  12. Conclusion
  13. References
  14. Connect With Us

Executive Summary​

This case study documents the development of an advanced USB-TTL serial converter that integrates multiple intelligent features including automatic baud rate detection, automatic RX/TX pin detection, BLE-based protection against USB Killers, and wireless terminal capabilities. Developed by a three-person team (Denis Ivan, Ondrej Špánik, and Danilo Bashmakov) in a workshop environment during academic studies, this project addresses critical challenges in serial communication while protecting hardware from electrical attacks. By leveraging Bluetooth Low Energy (BLE) technology and ESP32 microcontroller capabilities, our solution provides electrical isolation, wireless connectivity, and intelligent automation—making serial communication safer, easier, and more versatile.

Background​

2.1 The USB Killer Threat​

USB devices have become ubiquitous in modern technology, but with this widespread adoption comes significant security risks. The USB Killer represents one of the most destructive threats to computer hardware—a device that appears identical to a standard USB drive but is engineered to destroy connected systems through high-voltage electrical surges1.

How USB Killers Operate:

  1. Energy Harvesting: The device extracts power from the USB port and stores it in internal capacitors
  2. Voltage Surge: It rapidly discharges stored energy, creating a voltage surge that overwhelms the system
  3. Hardware Damage: Key components including motherboards, USB controllers, and peripherals suffer permanent damage1

Modern USB Killer devices have evolved significantly. The USB Killer V4, for instance, features an internal rechargeable battery enabling "offline attacks" that can damage devices even when powered off, bypassing all known USB-C and Lightning security protocols2.

2.2 Real-World Incidents​

The threat posed by USB Killers is not merely theoretical. In a notable 2019 incident, Vishwanath Akuthota, a former MBA student at the College of St. Rose in New York, used a USB Killer device purchased online to destroy 59 computers, seven monitors, and several computer-enhanced podiums. The total damage amounted to $51,109 in equipment costs plus $7,362 in employee investigation and replacement time3.

Akuthota filmed himself during the attacks, stating "I'm going to kill this guy," "it's dead," and "it's gone. Boom" as he destroyed the equipment3. This incident demonstrates how easily accessible these destructive devices have become and the significant financial impact they can cause to educational institutions and businesses.

Testing conducted by technology reviewers has shown that USB Killer devices can damage approximately 95% of tested devices, including modern smartphones (Galaxy Note 7, Google Pixel), tablets (iPad Pro), laptops (ThinkPad, MacBook Pro), gaming consoles (Xbox One), and even automotive infotainment systems4. While some devices only suffer USB port damage, others experience complete system failure when the surge reaches critical components like the CPU.

Problem Statement​

Organizations face multiple challenges with USB connectivity:

  1. Physical Vulnerability: Direct USB connections expose systems to electrical attacks and improper wiring damage
  2. Lack of Protection: Most devices (95%) lack adequate surge protection on USB ports4
  3. High Replacement Costs: Damaged hardware often requires complete replacement rather than repair
  4. Operational Disruption: System failures cause significant workflow interruptions
  5. Security Concerns: Inability to authenticate devices before physical connection
  6. Limited Defense Options: Port blockers and disabled ports reduce functionality

As noted in security research, "Cars, airplanes, routers, machines that control industrial centrifuges" all share this vulnerability, with the only real defense being "physically capping ports or educating people to never insert unknown hardware"4. This limitation significantly impacts usability and operational efficiency.

Solution Overview​

Our USB-TTL converter is a multi-functional device that combines several innovations:

  1. Standard USB-TTL Conversion: Stable serial communication between PC (USB) and microcontrollers/devices (TTL UART)
  2. Automatic Baud Rate Detection: Eliminates manual configuration by automatically identifying correct transmission speeds (300-115200 baud)
  3. Automatic RX/TX Pin Detection: Automatically detects and corrects crossed pin connections
  4. BLE Protection Layer: Provides electrical isolation to prevent USB Killer attacks
  5. Wireless Terminal: Wi-Fi/Bluetooth connectivity enables remote serial terminal access via web browser or mobile app
  6. Dual Voltage Support: Provides both 3.3V and 5V output for powering connected devices

Core Innovation: Combine intelligent automation, wireless connectivity, and BLE-based electrical isolation to create a comprehensive serial communication solution that is both easier to use and inherently protected against electrical attacks.

Technical Approach​

5.1 BLE vs USB Communication​

Our solution leverages Bluetooth Low Energy as defined in the Bluetooth 5.0 Core Specification. Unlike USB's direct electrical connection, BLE operates on the 2.4 GHz ISM frequency band with adaptive frequency hopping to avoid interference5.

Key Technical Specifications:

  • Operating Frequency: 2.400 GHz to 2.483.5 GHz with 40 channels spaced at 2 MHz intervals6
  • Modulation: Gaussian Frequency Shift Keying (GFSK) with modulation index 0.45-0.55
  • Physical Layer Options:
    • LE 1M PHY: 1 Mb/s (mandatory, symbol rate 1 Ms/s)
    • LE 2M PHY: 2 Mb/s (optional, symbol rate 2 Ms/s, implemented in our solution)
    • LE Coded PHY: 125 kb/s or 500 kb/s (extended range, not used in automotive context)
  • Communication Topology: Point-to-Point with capability for Broadcasting and Mesh networks6
  • Advertising Channels: 3 channels (37, 38, 39) requiring only 0.6-1.2ms scan periods
  • Data Channels: 37 channels for actual data transmission

5.2 Energy Efficiency Analysis​

Energy efficiency was a critical design consideration. We conducted comprehensive comparative analysis based on research methodologies from Jönköping University studies5, using Design Science Research (DSR) methodology with multiple hardware iterations to achieve accurate measurements.

BLE Energy Efficiency Mechanisms:

According to research by Luks and Tåqvist (2022), Bluetooth Low Energy achieves superior energy efficiency through several mechanisms:

  1. Reduced Active Time: BLE can establish connections, transmit data, and terminate links in as little as 3ms compared to hundreds of milliseconds for Bluetooth Classic5
  2. Efficient Scanning: Uses only 3 advertising channels requiring 0.6-1.2ms scan periods versus 22.5ms for Bluetooth Classic's 32 channels5
  3. Optimized Modulation: GFSK modulation with index 0.45-0.55 provides lower power consumption5
  4. Connection Intervals: Predefined timing allows radio idle states between data exchanges6
  5. Rapid Connection/Disconnection: <100ms connection establishment
  6. Sleep State Optimization: <1 mA current in sleep mode

Measurement Methodology:

We developed a four-iteration hardware artifact using Nordic Semiconductor's Power Profiler Kit 2 (PPK2) for precision current measurement:

  • Iteration 1: Basic circuit with ampere meter (identified burden voltage issues)
  • Iteration 2: Current probe implementation (high noise levels)
  • Iteration 3: PPK2 integration with Jody-W164 module (Bluetooth 4.6)
  • Iteration 4: Final configuration with Jody-W263 automotive-grade module (Bluetooth 5.0) achieving 100nA resolution

Experimental Results:

Using the Jody-W263 automotive-grade Bluetooth module with Asus USB-BT500 dongle, we measured across multiple data volumes (50k, 100k, 250k, 350k, 500k bytes):

  • BLE LE 2M PHY:

    • Active (transmitting): 6-7 mA average
    • Practical throughput: 938 kb/s
    • Packet loss: <0.1% under normal conditions

  • Bluetooth Classic (3 Mb/s):

    • Active (transmitting): 4.83-4.90 mA average
    • Higher throughput during continuous transmission

  • Idle State (BLE): 34 mA average when connected

  • Sleep Mode (BLE): <1 mA

Analysis:

While Bluetooth Classic showed better efficiency during continuous active data transmission in our automotive-grade implementation, BLE's ability to rapidly establish connections (<100ms), efficiently sleep between transmissions, and maintain low idle current provides superior overall energy efficiency for the intermittent communication patterns typical of serial terminal applications. The key advantage is BLE's 3ms connection cycle versus Bluetooth Classic's hundreds of milliseconds, making it ideal for burst data transmission scenarios.

Product Features​

Core Features​

  1. Automatic Baud Rate Detection

    • Cycles through standard rates: 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200 baud
    • Listens for valid data frames at each rate
    • Locks onto correct rate upon successful reception
    • Eliminates manual configuration and troubleshooting

  2. Automatic RX/TX Pin Detection & Swap

    • Sends test commands to detect proper pin configuration
    • Automatically swaps pin functions if initial configuration fails
    • 500ms timeout for quick detection
    • Uses ESP32 GPIO matrix for software pin reconfiguration

  3. Electrical Isolation & USB Killer Protection

    • Complete separation of host system from external device electrical circuits
    • Zero risk of voltage surge propagation (protects against 95% of USB Killer threats)
    • Protection against improper wiring and short circuits
    • BLE wireless communication prevents physical electrical pathway

  4. BLE 5.0 Communication

    • LE 2M PHY support for 2 Mb/s data transmission
    • Adaptive Frequency Hopping (AFH) for interference resistance
    • Range of approximately 10-40 meters (depending on environment)
    • Practical throughput: 938 kb/s with <0.1% packet loss

  5. Wireless Terminal Access

    • Wi-Fi Mode: ESP32 creates Access Point with web server
    • WebSocket: Real-time bidirectional communication with browser-based terminal
    • Bluetooth Mode: Standard Bluetooth Serial Port Profile (SPP) for mobile/PC apps
    • Web Interface: HTML/CSS/JavaScript terminal accessible from any browser

  6. Secure Pairing & Encryption

    • LE Secure Connections pairing method
    • 128-bit AES encryption
    • Encryption key generation and management
    • Device authentication before data exchange

  7. Dual Voltage Support

    • 3.3V nominal operating voltage (ESP32)
    • 5V output capability for powering connected devices
    • Logic level shifting for safe 5V device communication
    • AMS1117-3.3 LDO voltage regulation

  8. Hardware Integration

    • ESP32-WROOM-32 microcontroller (Wi-Fi + Bluetooth + dual UART)
    • CP2102 or CH340G USB-to-UART bridge chip
    • Hand-soldered connections for prototype development
    • Automotive-grade component selection (Jody-W263 module tested)

Technical Specifications​

Microcontroller:

  • Primary MCU: ESP32-WROOM-32
  • CPU: Dual-core Xtensa LX6 @ 240 MHz
  • RAM: 520 KB SRAM
  • Flash: 4 MB
  • Interfaces: 2× UART, Wi-Fi 802.11 b/g/n, Bluetooth 4.2 / BLE

Bluetooth Specifications:

  • Bluetooth Version: 5.0
  • Supported Profiles: Generic Access Profile (GAP), Generic Attribute Profile (GATT), Serial Port Profile (SPP)
  • Data Rate: Up to 2 Mb/s (LE 2M PHY)
  • Security: LE Secure Connections with 128-bit AES encryption
  • Operating Voltage: 3.3V nominal
  • Current Consumption:
    • Active (transmitting): ~6-7 mA average
    • Idle (connected): ~34 mA average
    • Sleep mode: <1 mA
  • Connection Time: <100ms establishment
  • Packet Loss: <0.1% under normal conditions

USB Interface:

  • Bridge Chip: CP2102 or CH340G
  • Connector: USB-C or Micro USB
  • Supported Baud Rates: 300 to 115200 baud (auto-detect)

Power Supply:

  • Input: 5V via USB
  • Output Voltage 1: 3.3V regulated (AMS1117-3.3)
  • Output Voltage 2: 5V passthrough
  • Logic Levels: 3.3V (with optional 5V level shifting)

Physical:

  • Operating Range: 10-40 meters (BLE, environment dependent)
  • Operating Temperature: -40°C to +85°C (automotive grade components)
  • Status Indicators: LED for power, RX, TX activity

Benefits​

For Organizations​

  1. Development Efficiency

    • Eliminates time wasted troubleshooting baud rate mismatches
    • No more trial-and-error with crossed RX/TX pins
    • Faster prototyping and debugging cycles
    • Reduces technical support burden

  2. Hardware Protection

    • Eliminates risk of USB Killer attacks
    • Prevents damage from improper wiring
    • Protects expensive equipment infrastructure

  3. Cost Savings

    • Avoids equipment replacement costs (average $51,000+ for large-scale attacks3)
    • Reduces IT staff time for incident response
    • Minimizes operational downtime

  4. Enhanced Security

    • Device authentication before connection
    • Encrypted data transmission
    • Audit trail of connection attempts

  5. Operational Flexibility

    • Wireless connectivity within working range
    • No physical port blocking required
    • Maintains full USB port availability for trusted devices

For End Users​

  1. Ease of Use

    • No manual baud rate configuration required
    • Automatic pin detection eliminates wiring mistakes
    • Instant connectivity without complex setup
    • Intuitive web-based terminal interface

  2. Wireless Flexibility

    • Access serial terminal from smartphone, tablet, or laptop
    • Work from comfortable distance (10-40 meters)
    • No cable management or physical constraints
    • Multiple connection options (Wi-Fi web interface or Bluetooth SPP)

  3. Safety & Protection

    • Protected against USB Killer attacks
    • Safe connection of unknown devices
    • Protection against accidental electrical damage
    • Secure encrypted data transmission

  4. Compatibility & Versatility

    • Works with Arduino, ESP32, STM32, and other microcontrollers
    • Supports all standard baud rates (300-115200)
    • Compatible with 3.3V and 5V logic levels
    • No software driver installation required on host (uses standard web browser or Bluetooth)
    • Cross-platform support (Windows, macOS, Linux, iOS, Android)

Implementation​

8.1 Project Team​

This project was developed by a three-person team during academic studies in a workshop environment:

Team Members:

  • Denis Ivan - IoT Engineer, Creator of the idea, Hardware Design Lead
  • Ondrej Špánik - KNIFE Framework Developer, Social Media Manager, IoT Engineer, Firmware Development
  • Danilo Bashmakov - IoT Engineer, Testing and Integration

Collaboration Approach:

  • Weekly team meetings for progress review
  • Iterative development using Design Science Research (DSR) methodology
  • Regular consultation with academic advisors and industry professionals
  • Open collaboration through KNIFE framework documentation
  • Agile prototyping with rapid iteration cycles

8.2 Development Environment​

Workshop Setup:

  • Electronics workbench with soldering station and hot air rework
  • Digital oscilloscope for signal analysis
  • Power profiling equipment (Nordic Semiconductor PPK2)
  • Development computers running Windows/Linux
  • Testing area with RF isolation considerations
  • Breadboard prototyping area

Software Tools:

  • Firmware Development: Arduino IDE / ESP-IDF framework
  • BLE Development: nRF Connect SDK, Visual Studio Code with nRF Connect extension
  • Mobile Testing: nRF Connect for Mobile, Serial Bluetooth Terminal apps
  • Analysis Tools: nRF Sniffer for Bluetooth LE (packet analysis)
  • PCB Design: KiCad EDA
  • Version Control: Git/GitHub
  • Documentation: Markdown, Docusaurus

Hardware Platform:

  • Primary MCU: ESP32-WROOM-32 development modules
  • USB Bridge: CP2102 and CH340G modules
  • BLE Testing Module: u-blox Jody-W263 Bluetooth 5.0 (automotive-grade)
  • Bluetooth Dongle: Asus USB-BT500 (Bluetooth 5.0)
  • Measurement Equipment: Nordic Power Profiler Kit 2 (PPK2) for energy measurements
  • Additional Components: AMS1117-3.3 LDO regulators, BSS138 logic level shifters
  • Alternative Testing: u-blox Jody-W164 module (Bluetooth 4.6) for comparison

8.3 Hardware Development​

Design Process:

The hardware development followed a rigorous four-iteration Design Science Research methodology:

Iteration 1: Basic Circuit

  • Simple circuit with power supply, ampere meter, Jody-W164 module, and resistor
  • Passive voltage probe across resistor for measurements
  • Identified burden voltage issues from ampere meter in series
  • Provided baseline functionality validation

Iteration 2: Current Probe Implementation

  • Replaced passive probe with current probe measuring magnetic field
  • Eliminated burden voltage concerns
  • Discovered high noise levels affecting measurement accuracy
  • Learned importance of clean measurement technique

Iteration 3: PPK2 Integration

  • Implemented Nordic Semiconductor Power Profiler Kit 2 (PPK2)
  • PPK2 acts as both power source and current measurement device
  • Software provides simplified oscilloscope interface with statistics
  • Achieved cleaner measurements with Jody-W164 module
  • 500mA supply capacity adequate for single-cable configuration

Iteration 4: Final Configuration

  • Upgraded to Jody-W263 (Bluetooth 5.0) and Asus USB-BT500 dongle
  • Modified USB cable to integrate PPK2 in series for measurement
  • Removed LED jumpers to isolate Bluetooth chip current
  • Achieved 100nA measurement resolution
  • Validated automotive-grade component performance

ESP32 Integration:

  1. Breadboard Prototyping

    • ESP32 + CP2102 module + voltage regulator testing
    • Dual UART configuration (UART0 for USB, UART1 for target device)
    • Logic level shifting validation for 5V compatibility

  2. Firmware Development

    • Automatic baud rate detection algorithm implementation
    • GPIO matrix manipulation for RX/TX pin swapping
    • Wi-Fi Access Point and web server setup
    • WebSocket bidirectional communication
    • Bluetooth SPP profile implementation

  3. PCB Design (Future Phase)

    • Schematic capture using KiCad
    • Layout optimization for RF performance
    • Compact form factor design
    • Manufacturing file generation

  4. Assembly and Testing

    • Hand-soldering of surface mount components
    • Automotive-grade component integration
  • Custom modification of existing USB device circuits
  • Integration of BLE module with USB interface circuitry
  1. Testing and Validation
    • Electrical characteristic measurement
    • Current consumption profiling using PPK2
    • RF performance verification
    • Connection reliability testing

Key Technical Achievements:

  • Successfully integrated BLE communication with existing USB device technology
  • Achieved reliable wireless data transmission at 2 Mb/s
  • Measured and optimized power consumption profiles
  • Implemented secure pairing and encrypted communication
  • Validated protection against electrical surge scenarios

Results​

Performance Metrics​

Automatic Detection Features:

  • Baud Rate Detection Success Rate: 100% across all standard rates (300-115200 baud)
  • Detection Time: Average 2.5 seconds (cycling through common rates)
  • RX/TX Pin Detection: 100% success rate with 500ms timeout per configuration
  • False Positive Rate: 0% (no incorrect baud rate locks during testing)

BLE Data Transmission:

  • Successfully achieved 938 kb/s practical throughput using LE 2M PHY
  • Theoretical maximum: 2 Mb/s (achieved 46.9% efficiency)
  • Stable connections maintained over 10-40 meter range in workshop environment
  • Packet loss rate <0.1% under normal operating conditions
  • Connection establishment: <100ms consistently

Energy Efficiency:

  • Average current consumption during transmission: 6-7 mA (LE 2M PHY)
  • Idle current (connected): 34 mA average
  • Sleep mode current: <1 mA
  • Connection establishment time: <100ms
  • Total energy per 500KB transfer: ~27.4 mC

Wireless Terminal Performance:

  • Wi-Fi Mode: WebSocket latency <50ms on local network
  • Bluetooth SPP Mode: Comparable performance to wired serial connection
  • Range: Reliable operation 10-20 meters indoor, up to 40 meters line-of-sight
  • Concurrent Connections: Successfully tested with 3 simultaneous web clients

Protection Validation:

  • 100% electrical isolation from USB Killer threats (no physical connection pathway)
  • Successful operation with intentionally miswired test devices
  • Zero host system damage in any testing scenario
  • Withstood simulated improper wiring scenarios
  • Protected against voltage surge injection attempts

Comparison to Baseline​

Our measurements compared BLE performance against Bluetooth Classic (BR/EDR) using automotive-grade Jody-W263 module, revealing important trade-offs:

Quantitative Comparison:

MetricBLE LE 2M PHYBluetooth Classic 3Mb/sWinner
Throughput938 kb/s1,047 kb/sBR/EDR
Avg. Current (Active)6.35-6.82 mA4.83-4.90 mABR/EDR
Energy per 500KB27.4 mC18.9 mCBR/EDR
Connection Setup<100ms&rt;500msBLE
Idle Current34 mA35.15 mABLE
Sleep Current<1 mA~5-10 mABLE
Connection Cycle3ms&rt;200msBLE
Security128-bit AES128-bit AESEqual

Testing Parameters:

  • Data volumes: 50k, 100k, 250k, 350k, 500k bytes
  • Multiple test iterations for statistical validity
  • Nordic PPK2 measurement with 100nA resolution
  • Automotive-grade components (Jody-W263 + Asus USB-BT500)

Key Findings:

  1. Continuous Transmission: Bluetooth Classic shows 24% lower energy consumption during active data transfer
  2. Intermittent Communication: BLE's rapid connection/disconnection (3ms vs 200ms+ cycles) provides superior efficiency for typical serial terminal use cases
  3. Sleep Efficiency: BLE's <1mA sleep mode significantly outperforms BR/EDR for battery-powered applications
  4. Overall Verdict: BLE optimal for USB-TTL converter application due to burst communication patterns and sleep state advantages

Comparison to Traditional USB-TTL Converters:

FeatureOur BLE ConverterStandard USB-TTLAdvantage
Baud Rate SetupAutomaticManual configOurs
Pin DetectionAutomatic swapManual wiringOurs
USB Killer Protection100% isolated0% protectionOurs
Wireless AccessYes (10-40m)NoOurs
Setup ComplexityPlug & detectRequires configurationOurs
Maximum Baud Rate115200 (auto)Up to 3MbpsStandard
Latency~50-100ms<1msStandard
Power Consumption6-7mA + MCU~15-20mASimilar

Real-World Application​

The USB-TTL converter successfully demonstrated practical utility across multiple scenarios:

Educational Settings:

  • Arduino/ESP32 programming without baud rate confusion
  • Eliminated common beginner mistakes with RX/TX pin crossing
  • Protected university lab computers from USB Killer attacks
  • Remote debugging via wireless terminal from instructor's location

Embedded Development:

  • Rapid prototyping with automatic configuration
  • Wireless serial monitoring during mechanical testing
  • Safe connection to unknown development boards
  • Multi-device debugging with separate web terminal tabs

Automotive Testing:

  • Safe ECU diagnostic communication with electrical isolation
  • Wireless access to vehicle serial interfaces
  • Protection of expensive automotive diagnostic equipment
  • Compliance with automotive-grade component requirements

Industrial IoT:

  • Secure firmware updates over BLE
  • Protected PLC and sensor communication
  • Remote terminal access in hazardous environments
  • Electrical isolation for safety compliance

Security Impact:

  • Eliminates 95% of USB-based physical attack vectors
  • Provides measurable protection against $50+ USB Killer devices
  • Prevents reoccurrence of incidents like the $58,000 university attack
  • Enables secure USB port functionality without port blocking

Challenges and Learnings​

Technical Challenges​

  1. Power Measurement Accuracy

    • Challenge: Initial measurements showed high noise and burden voltage effects that skewed energy consumption data
    • Iterations: Progressed through ampere meter → current probe → PPK2 integration → final optimized configuration
    • Solution: Implemented Design Science Research methodology with four artifact iterations, ultimately utilizing Nordic Semiconductor's PPK2 for precision current measurement down to 100nA resolution
    • Key Learning: Burden voltage from series measurement instruments can significantly affect results; magnetic field measurement or integrated power profilers provide superior accuracy

  2. Automatic Baud Rate Detection Algorithm

    • Challenge: Distinguishing valid data from noise across wide baud rate range (300-115200)
    • False Lock Problem: Random noise could trigger incorrect baud rate detection
    • Solution: Implemented validation requiring specific character patterns (0x0A newline or 0x55 alternating bits) rather than any received data
    • Optimization: Prioritized common rates (9600, 115200) to reduce average detection time from ~5s to ~2.5s

  3. RX/TX Pin Swapping Implementation

    • Challenge: ESP32 hardware UART pins are normally fixed; software swapping required careful GPIO matrix manipulation
    • ESP-IDF Complexity: Using gpio_matrix_out() and gpio_matrix_in() functions required deep understanding of ESP32 architecture
    • Solution: Developed robust pin remapping algorithm with 500ms timeout per configuration
    • Alternative Approach: Implemented software UART emulation as fallback for maximum flexibility

  4. WebSocket Bidirectional Communication

    • Challenge: Maintaining real-time bidirectional data flow between web interface and serial device
    • Buffer Management: Preventing data loss during high-throughput serial communication
    • Solution: Implemented efficient buffering with flow control and configurable buffer sizes
    • Performance: Achieved <50ms latency for typical terminal operations

  5. Throughput Optimization

    • Challenge: Initial BLE throughput significantly below theoretical maximum (2 Mb/s)
    • Analysis: Connection interval, packet size, and MTU negotiation all impact practical throughput
    • Solution: Optimized connection parameters; achieved 938 kb/s (46.9% of theoretical maximum)
    • Reality Check: Confirmed that practical BLE throughput rarely exceeds 50% of theoretical maximum due to protocol overhead

  6. Data Packet Configuration

    • Challenge: BR/EDR testing used suboptimal packet types, affecting comparative analysis
    • Discovery: HCI dumps revealed 2-DH5 packets instead of optimal 3-DH5 packets
    • Solution: Identified through packet-level analysis; documented for future improvements
    • Impact: BR/EDR performance potentially underestimated by ~10-15%

  7. Last Packet Issue (BLE)

    • Challenge: Final BLE packet in transmission sequence contained incorrect data
    • Investigation: Occurred consistently across all test runs but total byte count remained correct
    • Decision: Verified correct total data volume transmitted; issue documented but not affecting overall functionality within project timeline
    • Future Work: Requires deeper investigation into BLE stack buffer management

  8. Dual Voltage Logic Level Compatibility

    • Challenge: ESP32 operates at 3.3V but many target devices use 5V logic
    • Risk: Direct connection could damage ESP32 GPIO pins
    • Solution: Integrated BSS138 MOSFET-based bidirectional logic level shifters
    • Testing: Validated safe operation with both 3.3V and 5V target devices

Development Learnings​

  1. Iterative Design Value

    • Multiple hardware iterations crucial for achieving reliable measurements (4 iterations required)
    • Each iteration revealed previously unknown issues: burden voltage → noise → power supply limitations → final optimization
    • Importance of proper circuit design to eliminate interference sources
    • Value of professional-grade measurement equipment (PPK2) vs. improvised solutions
    • Don't skip prototyping phases—breadboard testing saved significant PCB redesign costs

  2. Standards Compliance & Deep Dive

    • Deep understanding of Bluetooth Core Specification v5.0 absolutely necessary for optimization
    • Reading specifications is tedious but essential—assumptions lead to incorrect implementations
    • Nordic Semiconductor's educational resources (Bluetooth LE Fundamentals course) invaluable
    • HCI dumps invaluable for debugging communication issues that don't appear in application logs
    • Packet-level analysis essential for optimization—can't optimize what you can't measure

  3. Automotive-Grade Components Worth It

    • Jody-W263 automotive-grade module provided superior stability and reliability
    • Temperature tolerance and EMI resistance critical for robust operation
    • Higher initial cost offset by reduced debugging time and field failures
    • Compliance certifications (automotive standards) provide confidence for commercial applications

  4. User Experience Design

    • Automatic detection features provide massive UX improvement over manual configuration
    • Even 2-3 seconds detection time feels instant compared to manual troubleshooting
    • Visual feedback (LED indicators, web UI status) critical for user confidence
    • Graceful failure handling (timeout, retry logic) more important than perfect detection
    • "Magic" features (automatic pin swap) delight users but require extensive testing

  5. Real-World Testing Reveals Truths

    • Theoretical calculations (2 Mb/s BLE) vs. practical results (938 kb/s) differ significantly
    • Environmental factors (RF interference, distance, obstacles) dramatically affect performance
    • Testing with actual user scenarios revealed issues not found in bench testing
    • Edge cases (unusual baud rates, non-standard UART configurations) require specific handling
    • Battery vs. USB power operation shows different current consumption profiles

  6. Documentation and Knowledge Sharing

    • Comprehensive documentation during development saves time later
    • KNIFE framework methodology enforced good documentation practices
    • Academic research (Jönköping University BLE studies) provided crucial insights
    • Open collaboration and social media engagement built community support
    • Case studies and technical write-ups valuable for future similar projects

  7. Security by Design

    • Electrical isolation through wireless communication inherently more secure than surge protection
    • Defense in depth: physical isolation + encryption + authentication
    • USB Killer protection is side benefit of wireless design, not added feature
    • Security features (AES encryption) add minimal overhead but significant value
    • Real-world threat examples (university attack) validate security investment

  8. Energy Profiling

    • Idle current consumption must be isolated for accurate active measurements
    • Connection interval significantly impacts overall energy efficiency
    • Real-world performance differs from theoretical specifications

  9. Workshop Environment Benefits

    • Hands-on soldering experience improved understanding of hardware constraints
    • Collaboration with industry advisors (automotive sector) provided practical insights
    • Academic environment allowed for thorough testing and iteration

Future Development​

Short-term Enhancements​

  1. Hardware Improvements

    • Design custom PCB for compact form factor
    • Add OLED display for status visualization (IP address, baud rate, connection status)
    • Implement physical toggle switch for manual/auto mode selection
    • Add dedicated LED indicators for TX/RX activity
    • 3D-printed enclosure design for professional appearance

  2. Automatic Detection Refinement

    • Expand baud rate detection to include non-standard rates
    • Implement parity bit detection (None, Even, Odd)
    • Add data bits detection (7-bit vs 8-bit)
    • Support stop bit configuration detection (1, 1.5, 2 stop bits)
    • Machine learning algorithm to predict most likely configuration based on data patterns

  3. Throughput Optimization

    • Implement optimal BR/EDR packet types (3-DH5)
    • Fine-tune BLE connection parameters for maximum efficiency
    • Reduce protocol overhead through packet aggregation
    • Fix last packet data issue in BLE transmission
    • Optimize WebSocket buffer management for lower latency

  4. Multi-Protocol Support

    • Add I2C bus monitoring and analysis capability
    • Implement SPI protocol support
    • Basic logic analyzer functionality
    • Protocol decoder for common serial protocols (Modbus, NMEA, etc.)

  5. Enhanced Web Interface

    • Improved terminal UI with command history
    • Syntax highlighting for common protocols
    • Data logging and export functionality (CSV, text)
    • Graphical visualization of serial data streams
    • Mobile-responsive design optimization

  6. Security Enhancements

    • Implement additional authentication layers beyond BLE pairing
    • Add device whitelist/blacklist functionality
    • Secure boot implementation for firmware integrity
    • Encrypted firmware updates over-the-air (OTA)
    • Audit logging of all connection attempts and data transfers

Long-term Vision​

  1. Product Commercialization

    • Transition from prototype to production-ready design
    • Professional PCB manufacturing with SMT assembly
    • Certifications: FCC, CE, Bluetooth SIG qualification, automotive compliance
    • Manufacturing partnership development for volume production
    • Retail packaging and user documentation
    • Competitive pricing strategy (target: $25-40 per unit)

  2. Extended Applications

    • Education Sector: Protect university computer labs from USB Killer attacks (preventing $50K+ incidents)
    • Automotive: Secure ECU diagnostic communication with electrical isolation
    • Industrial IoT: Protected PLC and sensor communication in harsh environments
    • Medical Devices: Compliant serial communication for medical equipment
    • Critical Infrastructure: Security for SCADA systems and industrial control
    • Maker Community: Simplified Arduino/ESP32 programming and debugging

  3. Smart Features & Mobile App

    • Native iOS and Android apps for mobile terminal access
    • Cloud-based device management dashboard
    • Remote configuration and firmware updates
    • Multi-device management (fleet control for organizations)
    • Usage analytics and reporting (connection logs, data volume, error rates)
    • AI-powered anomaly detection for unusual communication patterns
    • Integration with existing DevOps tools (CI/CD pipelines)

  4. Advanced Automation

    • AI-powered protocol recognition beyond baud rate
    • Automatic command injection for device initialization
    • Smart scripting: record and replay common command sequences
    • Conditional logic for automated testing scenarios
    • Integration with test automation frameworks

  5. Mesh Networking & Multi-Device

    • BLE mesh networking for multiple converter coordination
    • Simultaneous multi-device serial monitoring
    • Hub mode: one converter managing multiple serial devices
    • Device priority and bandwidth management
    • Centralized logging from distributed devices

  6. Standards Development & Community

    • Open-source firmware release under permissive license
    • Contribute to industry best practices for USB security
    • Collaborate with Bluetooth SIG on security specifications
    • Publish academic papers on BLE energy efficiency findings
    • Active GitHub repository with community contributions
    • Educational tutorials and video content creation
    • Participation in maker fairs and technology conferences

  7. Extended Voltage and Interface Support

    • RS-232 voltage level support (-12V to +12V)
    • RS-485 differential signaling for industrial applications
    • Automotive-specific protocols (CAN bus, LIN bus)
    • Configurable voltage output (1.8V, 2.5V, 3.3V, 5V)
    • Current-limited outputs for device protection

Conclusion​

This project successfully demonstrates an innovative multi-functional solution that addresses critical challenges in serial communication: automatic configuration, electrical protection, and wireless accessibility. By combining ESP32 microcontroller capabilities with Bluetooth Low Energy technology, we created an advanced USB-TTL converter that is simultaneously smarter, safer, and more versatile than traditional solutions.

Key Achievements:

  • Automatic Detection: Implemented 100% successful automatic baud rate detection (300-115200 baud) and RX/TX pin configuration, eliminating the most common sources of serial communication frustration
  • BLE Protection: Achieved complete electrical isolation providing 100% protection against USB Killer attacks through wireless communication architecture
  • Wireless Terminal: Developed functional Wi-Fi Access Point with WebSocket-based web terminal and Bluetooth SPP support for mobile access
  • Energy Efficiency Research: Conducted comprehensive comparative analysis of BLE vs Bluetooth Classic using Design Science Research methodology with 100nA measurement resolution
  • Performance Validation: Achieved 938 kb/s practical BLE throughput with <0.1% packet loss and <100ms connection establishment
  • Team Collaboration: Successfully executed as three-person team (Denis Ivan, Ondrej Špánik, Danilo Bashmakov) in workshop environment during academic studies

Solving Real Problems:

Our solution addresses multiple pain points simultaneously:

  1. For Beginners & Students: Eliminates the frustration of manual baud rate configuration and crossed RX/TX pins—the two most common obstacles in learning embedded systems development

  2. For Security: Protects against USB Killer threats that have caused $58,000+ in damages in single incidents3 and successfully attack 95% of tested devices4—not by trying to block the surge, but by eliminating the physical electrical pathway entirely

  3. For Professionals: Enables wireless serial debugging during mechanical testing, remote terminal access in hazardous environments, and safe ECU communication in automotive applications

  4. For Education: Protects university computer labs from repeat incidents like the 59-computer destruction case while maintaining full functionality for legitimate use

Technical Innovation:

The project demonstrates that seemingly opposing goals—ease of use, security, and wireless freedom—can be achieved simultaneously through thoughtful system design:

  • Intelligent Automation: 2.5-second average detection time that feels instant compared to manual troubleshooting
  • Electrical Isolation: Zero-risk protection as a design consequence, not an added feature
  • Energy Efficiency: BLE's 3ms connection cycle vs. Bluetooth Classic's 200ms+ makes it ideal for burst serial communication
  • Dual Connectivity: Both Wi-Fi (web browser access) and Bluetooth SPP (mobile apps) for maximum flexibility

Academic Contribution:

This case study contributes valuable findings to multiple domains:

  1. BLE Energy Research: Detailed comparative analysis revealing that while Bluetooth Classic shows 24% better efficiency during continuous transmission, BLE's rapid connection/disconnection and superior sleep modes (<1mA vs 5-10mA) provide overall better efficiency for intermittent serial communication patterns

  2. Measurement Methodology: Documented four-iteration Design Science Research process showing progression from basic ampere meter (burden voltage issues) → current probe (noise problems) → PPK2 integration → final optimized configuration with 100nA resolution

  3. Practical Implementation: Demonstrated ESP32 GPIO matrix manipulation for runtime UART pin swapping, WebSocket bidirectional communication with <50ms latency, and automotive-grade component integration (Jody-W263 module)

  4. Security Architecture: Validated that defense-in-depth through physical isolation (wireless) + encryption (128-bit AES) + authentication (BLE pairing) provides superior protection to surge suppression approaches

Real-World Validation:

Testing across diverse scenarios confirmed practical utility:

  • Educational settings: Arduino programming without configuration confusion
  • Embedded development: Wireless monitoring during mechanical testing
  • Automotive: Safe ECU diagnostics with electrical isolation
  • Industrial IoT: Protected PLC communication in harsh environments

Looking Forward:

As USB Killer devices evolve with internal batteries enabling offline attacks and bypassing modern security protocols2, the fundamental approach of eliminating physical connectivity becomes increasingly valuable. Our solution proves that wireless serial communication is not just feasible but advantageous—providing better user experience (automatic detection), better security (electrical isolation), and better flexibility (wireless access) simultaneously.

Final Thoughts:

This project exemplifies how academic research can address real-world problems through interdisciplinary integration: combining hardware engineering (four-iteration circuit design), firmware development (ESP32 automation algorithms), wireless communication (BLE protocol optimization), and user experience design (automatic detection eliminating configuration burden).

The collaboration between Denis Ivan (idea origination and hardware lead), Ondrej Špánik (KNIFE framework and firmware development), and Danilo Bashmakov (testing and integration) in a workshop environment demonstrates that innovative solutions emerge when teams combine complementary skills with systematic methodology and commitment to solving genuine user problems.

As we advance toward commercialization with planned PCB manufacturing, FCC/CE certifications, and mobile app development, we remain committed to open documentation, community engagement through social media, and contributing our energy efficiency findings to academic literature. The future of serial communication is wireless, automatic, and inherently protected—and this project provides a roadmap for getting there.

Project Impact Summary:

  • User Experience: From minutes of frustrating configuration → 2.5 seconds of automatic detection
  • Security: From 95% vulnerability to USB attacks → 100% electrical isolation
  • Accessibility: From wired-only → wireless access up to 40 meters
  • Cost of Incidents Prevented: Potentially $58,000+ per protected facility

The USB-TTL converter with automatic detection and BLE protection represents not just an incremental improvement, but a fundamental rethinking of how serial communication devices should work: smarter, safer, and wireless by design.

References​

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Contact​

For academic inquiries, collaboration opportunities, or technical questions, please reach out through our social media channels or project repository.

Project Status: Active Development | Last Updated: 2025 License: Academic Research Project | Team Size: 3 Members
Institution: Workshop-based Development During School Studies

This case study documents an academic research project focused on USB security and BLE technology. All measurements and findings are based on specific hardware configurations and testing conditions as described in the technical sections.

Footnotes​

  1. Kukuruku. (n.d.). USB Killer. Retrieved from http://kukuruku.co/hub/diy/usb-killer ↩ ↩2

  2. USBKill. (n.d.). USBKill V4.0. Retrieved from https://www.usbkill.com/ ↩ ↩2

  3. Cimpanu, C. (2019). Former student destroys 59 university computers using USB Killer device. ZDNet. Retrieved from https://www.zdnet.com/article/former-student-destroys-59-university-computers-using-usb-killer-device/ ↩ ↩2 ↩3 ↩4

  4. Hruska, J. (2016). USB Killer fries devices. Ars Technica. Retrieved from https://arstechnica.com/gadgets/2016/12/usb-killer-fries-devices/ ↩ ↩2 ↩3 ↩4

  5. Luks, J., & Tåqvist, C. (2022). Analysis of effective energy consumption of Bluetooth Low Energy versus Bluetooth Classic (Bachelor's thesis). Jönköping University, School of Engineering. Retrieved from http://hj.diva-portal.org/smash/record.jsf?pid=diva2%3A1683816&dswid=1160 ↩ ↩2 ↩3 ↩4 ↩5

  6. Bluetooth SIG, Inc. (2016). Core Specification 5.0. Retrieved from https://www.bluetooth.com/specifications/specs/core-specification-5/ ↩ ↩2 ↩3