The ATtiny85 Digispark Development Board is an ultra-compact, cost-effective micro-development board based on the Microchip ATtiny85 8-bit AVR microcontroller. Measuring less than one square inch, it is designed as a smaller, cheaper alternative to standard Arduino boards, making it an ideal choice for tiny, space-constrained electronics projects, wearable tech, and basic USB peripherals.Key Hardware SpecificationsThe board packs essential components into a miniature footprint, allowing you to run Arduino-based code without needing bulky external programmers:

• Microcontroller: Microchip ATtiny85.
• Core Clock Speed: Runs at 16.5 MHz or 20 MHz.
• Memory: 8 KB Flash memory (roughly 6 KB available after accounting for the onboard bootloader), 512 bytes of SRAM, and 512 bytes of EEPROM.
• Operating Voltage: 5V DC.
• Power Inputs: Can be powered via the USB port or through external sources. It features an onboard 5V regulator that can accept 7V to 35V (automatically regulated).
• Form Factor: Available in variants with a built-in PCB USB-A male plug, a Micro-USB port, or a Type-C USB port.

Pinout and I/O CapabilitiesThe board breaks out 6 General Purpose Input/Output (GPIO) pins (labeled P0 through P5). However, because the board lacks a dedicated USB interface chip (like the CH340), it uses software emulation to handle USB communication.

• USB Shared Pins: Pins P3 and P4 are physically tied to the USB data lines (\(D-\) and \(D+\)). If your project actively communicates with a PC over USB, you cannot use these pins for other hardware components.
• Analog Inputs (ADC): 4 pins can function as 10-bit analog-to-digital converter inputs.
• PWM Outputs: 3 pins support Hardware Pulse Width Modulation (more can be achieved via software PWM).
• Communication Protocols: Supports I2C and SPI via the Universal Serial Interface (USI) peripheral.
• Onboard Indicators: Features a Power LED and a built-in Test/Status LED tied to Pin P0 or P1 (depending on the specific board revision).

Programming and the Micronucleus BootloaderThe defining feature of the Digispark is its pre-flashed Micronucleus USB bootloader. This piece of software runs during the first few seconds of power-up to check if a computer is attempting to upload code.Because of how this bootloader works, the upload workflow differs slightly from standard Arduino boards:

1. You configure the Arduino IDE with the Digistump AVR board manager URL.
2. You click Upload in the IDE while the Digispark board is completely unplugged.
3. The IDE compiles the code and prompts you to plug in the board.
4. You plug the board into your computer’s USB port, and the bootloader catches the signal to flash the program.