Elfin is an ultra-compact ATSAMD21E18 development board desgined for makers, students, and embedded developers who need a decent microcontroller in smalled possible footprint.
Despite measuring only 22.2mm x 15.5mm, Elfin packs everything required for rapid prototyping:
- ATSAMD21E18 Microcontroller
- USB Type-C Connectivity
- 2MB External Flash
- 32.768kHz Crystal Oscillator + Internal clocks like: DFLL48M (48 MHz Booster)
- Fully Exposed GPIO
- 4-Layer PCB Design
Built for projects where every millimeter matters.
Most development boards are designed around convenience.
Elfin was designed around minimalism.
The goal was simple:
How small can a fully featured ATSAMD21 development board become?
The project explored compact embedded hardware design while maintaining usability, manufacutrability, and flexibility.
Inspired by:
- Tiny embedded systems
- Wearable electronics
- Open-source hardware
- Hack Club hardware projects
- Minimalist engineering
The result is a board that feels compact in size while remaining practical for real-world development. (Not the smallest tho 🤓)
- ATSAMD21E18 MCU
- USB Type-C
- 2MB External Flash
- 32.768kHz Crystal Oscillator
- 4-Layer PCB
- Breadboard Friendly
- SWD Programming Support
- Fully Exposed GPIO
- Open Source Hardware
- Ultra Compact Design (22.2mm x 15.5mm)
| Parameter | Value |
|---|---|
| MCU | ATSAMD21E18A |
| Internal Flash | 256KB |
| SRAM | 32KB |
| Crystal | 32.768kHz RTC Crystal |
| External Flash | 2MB External SPI Flash |
| USB | USB Type-C |
| Operating Voltage | 3.3V |
| PCB | 4 Layer PCB (Signal, Ground, Power, Signal) |
| Programming | UF2 / SWD |
| Power | USB Powered |
| Dimensions | 22.3mm x 15.5mm |
| No. | Quantity | Comment | Designator | Footprint | Value | Manufacturer Part | Manufacturer | Supplier Part | Supplier | Link |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 4 | 100nF | C1,C3,C6,C7 | C0402 | 100nF | CL05B104KB5NNNC | SAMSUNG(三星) | C1525 | LCSC | https://www.lcsc.com/product-detail/C1525.html |
| 2 | 3 | 1uF | C2,C4,C5 | C0402 | 1uF | CL05A105KA5NQNC | SAMSUNG(三星) | C52923 | LCSC | https://www.lcsc.com/product-detail/C52923.html |
| 3 | 2 | 10uF | C8,C9 | C0402 | 10uF | CL05A106MP5NUNC | SAMSUNG(三星) | C15525 | LCSC | https://www.lcsc.com/product-detail/C15525.html |
| 4 | 1 | USBLC6-2SC6 | D1 | SOT-23-6_L2.9-W1.6-P0.95-LS2.8-BR | USBLC6-2SC6 | USBLC6-2SC6 | ST(意法半导体) | C7519 | LCSC | https://www.lcsc.com/product-detail/C7519.html |
| 5 | 2 | castellated_holes_1x7 | H1,H2 | Carl Bugeja's Library.IntLib:castellated holes | castellated holes | N/A | N/A | N/A | Custom PCB Feature | N/A |
| 6 | 1 | USB_C_Receptacle_USB2.0_16P | J1 | Connector_USB:USB_C_Receptacle_HCTL_HC-TYPE-C-16P-01A | USB_C_Receptacle_USB2.0_16P | HC-TYPE-C-16P-01A | HCTL | C2894897 | LCSC | https://www.lcsc.com/product-detail/C2894897.html |
| 7 | 1 | 2.2uH | L1 | IND-SMD_L4.0-W4.0_XAL4030-332MEC | 2.2uH | SMNR4020-2.2UH | SXN(顺翔诺) | C135262 | LCSC | https://www.lcsc.com/product-detail/C135262.html |
| 8 | 3 | 10K | R1,R2,R3 | R0402 | 10K | RC0402FR-0710KL | YAGEO | C25744 | LCSC | https://www.lcsc.com/product-detail/C25744.html |
| 9 | 2 | 5.1K | R4,R5 | R0402 | 5.1K | RC0402FR-075K1L | YAGEO | C25905 | LCSC | https://www.lcsc.com/product-detail/C25905.html |
| 10 | 1 | 36.5K | R6 | R0402 | 36.5K | RC0402FR-0736K5L | YAGEO | C25793 | LCSC | https://www.lcsc.com/product-detail/C25793.html |
| 11 | 1 | EVPAWCD40 | SW1 | KEY-SMD_L3.0-W2.0-LS3.5 | EVPAWCD40 | EVPAWCD40 | PANASONIC(松下) | C2858606 | LCSC | https://www.lcsc.com/product-detail/C2858606.html |
| 12 | 1 | ATSAMD21E18A-MUT | U1 | QFN-32_L5.0-W5.0-P0.50-TL-EP3.6 | ATSAMD21E18A-MUT | ATSAMD21E18A-MUT | MICROCHIP(美国微芯) | C2052801 | LCSC | https://www.lcsc.com/product-detail/C2052801.html |
| 13 | 1 | W25Q16JVUXIQ | U2 | USON-8_L3.0-W2.0-P0.50-BL-EP | W25Q16JVUXIQ | W25Q16JVUXIQ | Winbond(华邦) | C2843335 | LCSC | https://www.lcsc.com/product-detail/C2843335.html |
| 14 | 1 | TPS63900DSKR | U3 | WSON-10_L2.5-W2.5-W0.50-TL-EP | TPS63900DSKR | TPS63900DSKR | TI(德州仪器) | C1518762 | LCSC | https://www.lcsc.com/product-detail/C1518762.html |
| 15 | 1 | 32.768KHz | X1 | OSC-SMD_L3.2-W1.5 | 32.768KHz | ABS07-32.768KHZ-T | Abracon | C9900004736 | LCSC | https://www.lcsc.com/product-detail/Crystals_ABRACON-ABS07-32-768KHZ-T_C9002.html |
The PCB was designed with one objective:
Maximum functionality in minimum space.
It has
- SWD debugging interface
- Optimized 4-layer routing
Navigate to:
./PCB/ElfinGerber.zipUpload the Gerber files to your preferred PCB manufacturer.
All required components can be found in:
./PCB/ElfinBOM.csvRecommended tools:
- Flux
- Fine-tip Soldering iron
- Tweezers
- Hot air station
Assembly order:
- Passive components
- Crystal oscillator
- Flash memory
- Voltage regulator
- ATSAMD21E18
- USB Type-C connector
Before powering:
- Check for shorts
- Verify USB connections
- Inspect power rails
- Confirm crystal orientation
Using an SWD programmer:
- Connect SWDIO
- Connect SWCLk
- Connect GND
- Flash teh UF2 bootloader
Once the bootloader is installed:
- Connect USB Type-C
- Enter bootloader mode
- Drag and drop the firmware
Elfin is perfect for:
- Wearables
- USB Devices
- Sensor Nodes
- Robotics
- IoT Projects
- Custom Controllers
- Educational Projects
- Compact Embedded Systems
Elfin/
├── PCB/
├── CAD/
├── Firmware/
├── Assets/
└── README.mdME.md- Initial Concept
- Schematic Design
- PCB Design
- Final Build
- Community Testing
Contributions, suggestions, and feedback are welcome.
If you'd like to improve Elfin:
git clone https://github.com/Sudo-Aju/Elfin.git
cd Elfin- Create a feature branch
- Make your changes
- Commit your work
- Open a pull request
Built with ❤️ for:
- Embedded Systems
- PCB Design
- Open Source Hardware
- Tiny Things
This project is licensed under the MIT License.
