A custom PCB clone of the Digispark development board — a minimal ATtiny85-based microcontroller board with native USB programming support. Designed from scratch in KiCad.
The original Digispark is a tiny Arduino-compatible board built around the ATtiny85. This is a custom PCB recreation of that design, including the USB low-speed interface circuit for programming directly over USB without a separate programmer.
The board breaks out all available ATtiny85 GPIO pins to two 4-pin headers for connecting peripherals.
[USB Connector] → [USB Protection Circuit] → [ATtiny85] → [GPIO Headers]
ATtiny85 Microcontroller 8-pin AVR MCU running at up to 16.5 MHz (internal PLL clock when using Micronucleus bootloader). 6 usable GPIO pins (PB0–PB5), supports I2C, SPI, PWM, and ADC.
USB Interface USB low-speed (1.5 Mbps) is bit-banged in software by the Micronucleus bootloader. The hardware side requires:
- Two 68Ω series resistors on D+ and D− lines (impedance matching)
- Two 3.6V Zener diodes (D1, D2) clamping the data lines to USB-safe voltage levels
- 1.5kΩ pull-up resistor (R4) on D+ to signal low-speed device to the host
Decoupling 100nF capacitor (C1) on the VCC pin filters supply noise close to the MCU.
GPIO Headers J1 and J2 break out all ATtiny85 pins for connecting sensors, displays, or other peripherals.
| Pin | ATtiny85 | Function |
|---|---|---|
| PB0 | Pin 5 | GPIO / PWM / AREF |
| PB1 | Pin 6 | GPIO / PWM |
| PB2 | Pin 7 | GPIO / I2C SDA / ADC1 |
| PB3 | Pin 2 | GPIO / ADC3 |
| PB4 | Pin 3 | GPIO / ADC2 |
| PB5 | Pin 1 | GPIO / RESET |
Designed in KiCad 9.0.2. Full schematic and PCB layout files included in the repository.
Flash using the Micronucleus bootloader over USB, or use any AVR ISP programmer via the RESET/SPI pins on the header.
Compatible with Arduino IDE using the Digistump ATtiny85 board package.
- USB low-speed electrical interface design (D+/D− termination, Zener clamping)
- ATtiny85 minimal circuit requirements
- PCB design for USB-connected embedded hardware in KiCad
- Impedance-sensitive routing for USB data lines