Digispark USB Development Board
Overview
The Digispark USB Development Board is a compact, low-cost microcontroller platform based on the ATtiny85. It provides USB connectivity, full Arduino IDE compatibility, and is ideal for small embedded and automation projects that require minimal hardware and fast prototyping. Its small form factor and simple programming interface make it perfect for both educational use and rapid hardware experimentation.
Key Features
- Powered by ATtiny85 microcontroller (8-bit RISC architecture)
- USB interface for direct programming — no external programmer needed
- Fully compatible with Arduino IDE via Micronucleus bootloader
- 6 I/O pins with PWM, ADC, and I2C support
- Onboard power regulation and protection
- Onboard LED for status indication and quick testing
- 5V operating voltage, can run from USB or external power
- Compact size and breadboard-friendly layout
Technical Details
Microcontroller: ATtiny85 (8 KB Flash, 512 B SRAM, 512 B EEPROM)
Clock Speed: 16.5 MHz (internal oscillator)
Power Supply: 5V via USB or 7–12V external source
USB Interface: Built-in via software emulation (V-USB)
Bootloader: Micronucleus (supports Arduino IDE)
Protection: 3.6V Zener diodes for USB line voltage regulation
Connectivity: 6 GPIO pins supporting PWM, ADC, I2C, and digital I/O
Hardware Components
Schematic, PCB & Gerber
Below is the schematic of the Digispark USB board. The design includes a minimal USB interface using resistors and zener diodes for voltage clamping, with the ATtiny85 directly handling USB communication through the V-USB stack. The PCB layout follows a compact form factor suitable for breadboard use.
Digispark USB Schematic
Digispark USB PCB
Challenges & Improvements
USB Stability: Early prototypes showed unreliable USB enumeration on some systems. Adjusting resistor tolerances and trace length improved consistency.
Firmware Upload: Occasional upload timeouts were mitigated by adding a small capacitor across the reset line to stabilize voltage transitions.
Power Noise: Added decoupling capacitors near the ATtiny85 to reduce noise from USB power.
Future Improvements: Integrate onboard voltage regulator for wider input range, add reset button, and optional micro-USB connector for improved durability.