PegorK/f32: A 9.85mm ESP32-C3 Board Built for WiFi Research

PegorK/f32: A 9.85mm ESP32-C3 Board Built for WiFi Research

The ESP32 ecosystem has no shortage of development boards, yet most follow predictable design patterns: breakout headers, generous GPIO access, and antenna circuits that play by the rules. For developers researching wireless systems or pushing hardware miniaturization to its limits, these conventional boards often carry unnecessary bulk and complexity. PegorK/f32 takes a deliberately different path—a research-oriented ESP32-C3 board so compact it mounts directly behind a USB-C receptacle, measuring just 9.85 mm × 8.45 mm.

Created by GitHub user PegorK, this open-source hardware project (630 stars, 38 forks, MIT License) functions as both a functional WiFi development platform and an intentional stress test of ESP32 design boundaries. The board sacrifices standard best practices—proper decoupling, antenna matching, USB termination resistors—to achieve its extreme form factor, making it a fascinating case study for embedded engineers exploring what's possible when conventional constraints are deliberately ignored.

This article examines the f32's technical design, build process, firmware capabilities, and the practical realities of deploying a board that prioritizes minimalism over robustness.

What is PegorK/f32?

PegorK/f32 is an ultra-compact ESP32-C3FH4 development board designed to mount directly behind a USB-C connector, with a PCB footprint smaller than most discrete components on typical dev boards. The project resides at https://github.com/PegorK/f32 and represents a hybrid of functional hardware and experimental engineering.

The board's creator developed it for personal research and as a learning exercise, specifically to gain experience with 01005-sized components (0.4mm × 0.2mm) after accidentally ordering them years prior. This origin story shapes the project's character: it's not positioned as a production-ready platform but as an exploration of physical and electrical limits.

Technical specifications from the repository:

• Microcontroller: ESP32-C3FH4 (RISC-V single-core, 160 MHz, 2.4 GHz WiFi/Bluetooth 5 LE)
• Dimensions: 9.85 mm × 8.45 mm PCB
• Thickness: 0.6 mm
• Exposed I/O: Single GPIO connected to onboard LED
• Primary interface: USB-C (power and data)
• Wireless: 2.4 GHz WiFi (functional with antenna modification)
• License: MIT License
• Last commit: 2025-11-30

The board's most distinctive characteristic is its intentional violation of standard design guidelines. The creator explicitly notes that the design "neglects several fundamental components such as proper decoupling capacitors, an antenna matching circuit, USB termination resistors, and likely more." This honesty about limitations is refreshing and technically informative—it establishes appropriate expectations for anyone considering the project.

The f32's relevance extends beyond its novelty. For developers studying [INTERNAL_LINK: ESP32-C3 miniaturization techniques], it demonstrates practical trade-offs between size, functionality, and RF performance. For the broader embedded community, it illustrates how modern PCB manufacturing capabilities (4/4 mil track/spacing, 0.2mm minimum holes) enable increasingly aggressive form factors.

Key Features

Extreme Miniaturization

The f32's 9.85 mm × 8.45 mm footprint achieves its compactness through several unconventional choices. The USB-C receptacle dominates one edge, with the ESP32-C3FH4, antenna, and LDO regulator packed into the remaining space. The creator notes a coincidental alignment: the ESP32 chip, antenna, and LDO are all "C3" models—a serendipitous naming convergence that simplified sourcing.

Single-GPIO Architecture

Unlike general-purpose dev boards, the f32 exposes only one GPIO, hardwired to an onboard LED. This radical simplification reflects the board's intended use case: WiFi and web-based applications where physical I/O expansion isn't required. The LED serves as the sole local output mechanism, with all interaction occurring through wireless interfaces.

Captive Portal Firmware

The included example application transforms the f32 into a WiFi captive portal. On power-up, it broadcasts an open access point; connecting clients are redirected to a local control interface. This firmware demonstrates practical functionality despite the hardware constraints.

01005 Component Challenge

The board uses 01005 passive components (resistors, capacitors), among the smallest standard surface-mount packages available. This choice was deliberate—the creator wanted a project that justified using parts accidentally purchased years earlier. The build documentation includes detailed hand-soldering techniques for these challenging components.

Documented RF Limitations and Workarounds

The repository contains honest documentation of the board's RF performance issues. Initial prototypes failed to connect or broadcast reliably due to "poor antenna circuitry or lack of." The creator resolved this through a manual antenna modification: soldering a bent wire to the chip antenna's end lead, floating above the first lead. Range testing achieved approximately 120 feet in clear line-of-sight conditions at 3 feet elevation—functional but modest compared to properly matched designs.

Accessible Manufacturing

The complete design files (Gerber, BOM, reference diagrams) and manufacturing parameters enable replication. The creator's 5-board PCBWay order cost $10.75 shipped, demonstrating that extreme miniaturization doesn't require extreme budgets when leveraging modern fabrication services.

Use Cases

WiFi Research and Education

The f32 serves as a tangible platform for studying ESP32-C3 behavior under non-ideal conditions. Students and researchers can observe how RF performance degrades without proper antenna matching, how power delivery behaves with minimal decoupling, and where the practical limits of component miniaturization lie. The documented workarounds provide teaching moments about engineering judgment versus textbook solutions.

Captive Portal and Web Interface Prototyping

With its included firmware, the f32 enables rapid prototyping of WiFi-based interaction systems. The captive portal pattern—broadcasting an AP, capturing connections, serving a local web interface—applies to configuration wizards, temporary access points, and IoT device onboarding flows. The single LED provides sufficient feedback for basic state indication.

Physical Security and Access Control

The board's diminutive size suggests applications where concealment matters. A USB-C port behind furniture, inside equipment enclosures, or embedded in structural elements could host the f32 for localized wireless services. The limited I/O is acceptable for simple beaconing, credential verification, or trigger-based actions.

Manufacturing Skill Development

For engineers developing fine-pitch hand-assembly capabilities, the f32 represents a structured challenge. The build documentation provides a progression from flux application through hotplate reflow to rework station techniques. Successfully assembling 01005 components with basic equipment builds transferable skills for repair and prototype work.

Form Factor Exploration

Product designers evaluating extreme miniaturization for commercial projects can use the f32 as a reference point. The repository documents which features survive aggressive size reduction, which require compromise, and which fail entirely. This empirical data complements theoretical design guidelines.

Installation & Setup

The f32 requires physical assembly before firmware deployment. The repository provides complete manufacturing documentation; this section covers the flashing procedure for the example application.

Prerequisites

• Assembled f32 board with USB-C connection
• Computer with esptool.py installed (version 4.0 or later)
• USB-C cable and appropriate serial port access

Firmware Flashing

Navigate to the repository's base directory, where the firmware/ folder contains three binary files. Execute the following command, substituting <PORT> with your system's device path:

# Windows example: COM5
# Linux example: /dev/ttyACM0
esptool.py -p <PORT> -b 460800 --before default_reset --after hard_reset --chip esp32c3 write_flash --flash_mode dio --flash_freq 80m --flash_size 2MB 0x0 firmware/bootloader.bin 0x10000 firmware/f32_internal.bin 0x8000 firmware/partition-table.bin

Command breakdown:

• -p <PORT>: Serial port for device communication
• -b 460800: Baud rate for faster flashing
• --chip esp32c3: Target microcontroller variant
• --flash_mode dio: Dual I/O flash access mode
• --flash_freq 80m: 80 MHz flash clock
• --flash_size 2MB: Allocated flash capacity
• 0x0 firmware/bootloader.bin: Bootloader at standard offset
• 0x10000 firmware/f32_internal.bin: Application firmware
• 0x8000 firmware/partition-table.bin: Partition table configuration

Alternative Development Paths

The repository notes that developers may use ESP-IDF VSCode extension or Arduino IDE for custom firmware development. These paths require standard ESP32-C3 toolchain configuration without f32-specific modifications.

Real Code Examples

The repository's firmware is distributed as precompiled binaries rather than source code. The following examples represent documented operational sequences from the README rather than extractable code snippets.

Example 1: Captive Portal Boot Sequence

The f32's example application implements a standard captive portal pattern. While source isn't provided, the documented behavior follows this logical structure:

// Conceptual representation based on README description
// Actual implementation not provided in repository

void setup() {
    // Initialize ESP32-C3 in AP mode
    WiFi.softAP("f32-AP", NULL);  // Open network, no password
    
    // Configure DNS captive portal redirect
    dnsServer.start(53, "*", WiFi.softAPIP());
    
    // Start web server on port 80
    server.on("/", handleRoot);
    server.on("/wifi", handleWiFiScan);
    server.on("/led", handleLED);
    server.on("/about", handleAbout);
    server.begin();
}

void loop() {
    dnsServer.processNextRequest();
    server.handleClient();
}

The README confirms this behavior: the device broadcasts an open AP, connected clients are automatically redirected to the control page, and the interface provides LED control, WiFi scanning, and device information.

Example 2: esptool Flashing Command

The repository's primary "code" is the flashing command itself, which serves as the interface between developer and hardware:

# Complete flashing command from repository documentation
# Execute from repository root directory

esptool.py \
    -p /dev/ttyACM0 \              # Linux serial port; use COM5 for Windows
    -b 460800 \                    # High baud rate for speed
    --before default_reset \       # Standard reset sequence
    --after hard_reset \           # Hard reset after flashing
    --chip esp32c3 \               # Explicit chip target
    write_flash \                  # Operation mode
    --flash_mode dio \             # Dual I/O for reliability
    --flash_freq 80m \             # 80 MHz flash clock
    --flash_size 2MB \             # Match ESP32-C3FH4 configuration
    0x0 firmware/bootloader.bin \  # Bootloader base address
    0x10000 firmware/f32_internal.bin \  # Application offset
    0x8000 firmware/partition-table.bin   # Partition table offset

This command exemplifies production ESP32 flashing patterns: separate binary segments at specific offsets, explicit chip identification, and post-flash reset configuration. The 2MB flash size reflects the ESP32-C3FH4's integrated configuration.

Note: The repository contains these two operational examples. Developers seeking additional code samples should refer to [INTERNAL_LINK: ESP32-C3 Arduino core documentation] or ESP-IDF examples for patterns applicable to the f32's single-GPIO constraint.

Advanced Usage & Best Practices

Antenna Modification Requirements

The README explicitly states that stock RF performance is inadequate for reliable operation. The documented workaround—soldering a bent wire extension to the chip antenna—should be considered mandatory rather than optional. Engineers replicating this project should:

• Use insulated wire to prevent shorting against nearby components
• Maintain the described geometry: soldered to end lead, floating above first lead
• Test range in your specific environment; the 120-foot result reflects ideal conditions

Assembly Sequence Optimization

The creator's documented build process emphasizes flux-heavy, stencil-free assembly for 01005 components. This approach contradicts conventional wisdom but proves effective at this scale:

• Apply flux liberally across entire board surfaces
• Pre-tin pads with fine solder wire before component placement
• Use optical magnification (microscope or quality loupe) throughout
• Place smaller components before larger ones to maintain access
• Consider hotplate for top side, rework station for bottom side due to USB-C connector interference

Power and Decoupling Realities

The intentional omission of proper decoupling capacitors means the f32 may exhibit voltage rail instability under load. For WiFi transmission bursts, this manifests as potential resets or failed associations. The creator notes functionality was achieved despite these omissions, but margin is minimal. Applications requiring reliability should consider external power conditioning or accept the experimental nature.

GPIO Expansion Limitations

With only one exposed GPIO (LED), the f32 is unsuitable for sensor-heavy applications. Future repository updates may add side-exposed GPIO pads, but current hardware requires wireless-centric architectures. Design applications around the captive portal pattern rather than attempting local peripheral expansion.

Comparison with Alternatives

The f32 occupies a distinct niche: it's not competing with production dev boards on convenience or capability, but rather exploring what's achievable when standard assumptions are discarded. The QT Py and M5Stamp offer superior out-of-box experience and GPIO flexibility; the f32 offers unmatched size and educational value in constraint-driven design.

FAQ

What ESP32 variant does the f32 use? The ESP32-C3FH4, a single-core RISC-V MCU with 2.4 GHz WiFi and Bluetooth 5 LE.

Can I use the f32 without soldering the antenna wire? Per the README, initial prototypes failed to connect or broadcast without the wire modification. Consider it required for reliable operation.

How do I program custom firmware? Use ESP-IDF VSCode extension or Arduino IDE with standard ESP32-C3 board selection. The USB-C connection provides serial access.

Is the f32 suitable for commercial products? The creator explicitly states it "intentionally neglects several fundamental components." Treat it as experimental/research hardware, not production-ready.

What's the actual wireless range? Approximately 120 feet clear line-of-sight at 3 feet elevation with the antenna modification. Your results will vary with environment.

What license covers the f32? MIT License, permitting commercial use, modification, and distribution with attribution.

Where can I get PCBs manufactured? The creator used PCBWay with 0.6mm thickness, 0.2mm minimum holes, and 4/4 mil track/spacing. Gerber files are in the hardware/ folder.

Conclusion

PegorK/f32 is not a board for every project, nor does it attempt to be. It succeeds precisely because it commits to a specific vision: how small can an ESP32-C3 functional WiFi device become when conventional design wisdom is deliberately set aside? The answer—9.85 mm × 8.45 mm, with documented caveats—provides genuine value for embedded engineers, researchers, and makers exploring hardware limits.

The project's strengths lie in its transparency about limitations, complete manufacturing documentation, and functional proof-of-concept firmware. Its weaknesses—single GPIO, required antenna modification, omitted decoupling—are not oversights but intentional trade-offs explicitly communicated by the creator.

This board best serves developers who: understand RF fundamentals enough to appreciate the antenna workaround, possess or wish to develop fine-pitch soldering skills, need ultra-compact WiFi functionality without peripheral expansion, or study constraint-driven engineering as a discipline.

For those ready to explore the f32's capabilities and limitations firsthand, the complete design files, build instructions, and precompiled firmware await at https://github.com/PegorK/f32.