Digispark ATtiny85: The Smallest Arduino-Compatible Board

The first time I held a Digispark ATtiny85, I couldn’t believe something this tiny could run Arduino code. Smaller than my thumbnail and costing less than a cup of coffee, this board has become my go-to solution for projects where a full-size Arduino would be overkill.

The Digispark ATtiny85 is a microcontroller development board created by Digistump that packs surprising capability into an impossibly small package. Based on the ATtiny85 chip from Microchip (formerly Atmel), it plugs directly into your computer’s USB port for programming and power. No cables, no external programmers—just plug it in and upload your sketch.

What Makes the Digispark ATtiny85 Special?

Unlike traditional Arduino boards that require USB-to-serial converter chips, the Digispark ATtiny85 implements USB communication entirely in software through an ingenious solution called V-USB. This software-defined USB interface, combined with the Micronucleus bootloader, eliminates the need for additional hardware and keeps the board incredibly compact.

The original Digispark measures approximately 25mm x 18mm—smaller than a standard USB flash drive. Some clones are even tinier. Despite this miniature footprint, the board includes an onboard 500mA voltage regulator, status LED, and all the circuitry needed for USB programming.

For makers working on space-constrained projects, the Digispark ATtiny85 opens possibilities that simply don’t exist with larger boards. I’ve embedded these in wearables, hidden them inside keyboard enclosures, and built standalone USB devices that disappear into the port they’re plugged into.

Digispark ATtiny85 Technical Specifications

Understanding the hardware capabilities helps determine if the Digispark ATtiny85 fits your project requirements:

Specification	Value
Microcontroller	ATtiny85
Architecture	8-bit AVR RISC
Operating Voltage	5V
Clock Speed	16.5 MHz (internal oscillator)
Flash Memory	8 KB (6 KB usable after bootloader)
SRAM	512 bytes
EEPROM	512 bytes
I/O Pins	6 (P0 to P5)
PWM Channels	3 (P0, P1, P4)
ADC Channels	4 (10-bit resolution)
USB Interface	V-USB (software-defined)
Input Voltage (VIN)	7V – 35V (12V recommended max)
Board Dimensions	~25mm x 18mm
Price Range	$1 – $5 USD

The 6KB usable flash sounds limiting, but many practical applications fit comfortably within this constraint. The bootloader occupies roughly 2KB, leaving enough space for LED controllers, sensor readers, USB HID devices, and automation scripts.

Digispark ATtiny85 Pinout Guide

The Digispark ATtiny85 pinout requires careful attention since pins serve multiple functions. Two pins (P3 and P4) handle USB communication, which affects their availability during active USB sessions.

Complete Pin Function Table

Pin	Digital	Analog	PWM	Special Functions	Notes
P0	D0	—	Yes	SDA (I2C), AREF	LED on older revisions
P1	D1	—	Yes	MISO, DO	LED on Rev 2/3/4
P2	D2	A1	—	SCK, SCL (I2C)	Analog input
P3	D3	A3	—	USB+	Shared with USB D+
P4	D4	A2	Yes	USB-	Shared with USB D-
P5	D5	A0	—	Reset (default)	Only 3V output on clones

USB Pin Sharing Explained

P3 and P4 connect to the USB data lines. During programming, these pins handle USB communication. Once your sketch runs, you can use them as regular I/O—but only if your code doesn’t actively communicate over USB. If you need all six pins, avoid USB serial communication in your final application.

Revision Differences

The onboard LED location varies by board revision:

Revision	LED Pin	Reset Pin (P5)
Original (no marking)	P0	Disabled (6 I/O available)
Rev 2	P1	Disabled (6 I/O available)
Rev 3 (clones)	P1	Enabled (5 I/O available)
Rev 4	P1	Disabled (6 I/O available)

Most inexpensive clones are Rev 3 variants with P5 functioning as reset rather than I/O. This limits you to five usable pins unless you modify fuse settings—a process that requires a high-voltage programmer to reverse if something goes wrong.

Setting Up Arduino IDE for Digispark ATtiny85

Programming the Digispark ATtiny85 works through the standard Arduino IDE with some additional board definitions. Here’s the setup process:

Step 1: Install Digispark Drivers

Windows users need libusb drivers before the board will be recognized:

1. Download drivers from the Digistump GitHub repository
2. Extract and run DPinst64.exe (64-bit) or DPinst.exe (32-bit)
3. Verify installation in Device Manager under “libusb-win32 devices”

Mac and Linux users typically don’t need additional drivers, though Linux may require udev rules for non-root access.

Step 2: Add Board Manager URL

Open Arduino IDE and navigate to File → Preferences. In the “Additional Board Manager URLs” field, add:

https://raw.githubusercontent.com/digistump/arduino-boards-index/master/package_digistump_index.json

Step 3: Install Digistump AVR Boards

Go to Tools → Board → Boards Manager, search for “Digistump,” and install “Digistump AVR Boards.”

Step 4: Select the Board

Choose Tools → Board → Digistump AVR Boards → Digispark (Default – 16.5 MHz).

Important Upload Procedure

The Digispark ATtiny85 upload process differs from standard Arduino boards:

1. Write your sketch
2. Click Upload (do NOT plug in the board yet)
3. Wait for “Plug in device now… (will timeout in 60 seconds)”
4. Insert the Digispark into a USB port
5. Wait for “Micronucleus done. Thank you!”

This sequence exists because the bootloader only listens for uploads during a 5-second window after power-up. Miss that window, and the board starts running your existing sketch.

Digispark ATtiny85 vs Arduino Uno Comparison

Understanding the tradeoffs helps determine when the Digispark ATtiny85 makes sense:

Feature	Digispark ATtiny85	Arduino Uno
Microcontroller	ATtiny85	ATmega328P
Clock Speed	16.5 MHz	16 MHz
Flash Memory	8 KB (6 KB usable)	32 KB (31.5 KB usable)
SRAM	512 bytes	2 KB
EEPROM	512 bytes	1 KB
Digital I/O	6	14
Analog Inputs	4	6
PWM Pins	3	6
Hardware Serial	No	Yes
Hardware I2C	No (USI-based)	Yes
USB Programming	Built-in (V-USB)	Via USB-Serial chip
Price	$1-5	$20-25
Size	~25 x 18 mm	68.6 x 53.4 mm

The Digispark ATtiny85 sacrifices memory, pins, and hardware peripherals for size and cost advantages. It doesn’t replace the Arduino Uno—it complements it for applications where minimal resources suffice.

Practical Digispark ATtiny85 Projects

The Digispark ATtiny85’s native USB capability enables unique applications impossible with boards lacking direct USB access.

USB HID Keyboard Emulation

The most popular Digispark ATtiny85 application is keyboard emulation. Using the DigiKeyboard library, the board can send keystrokes to any computer:

#include “DigiKeyboard.h”

void setup() {

  pinMode(1, INPUT_PULLUP);

}

void loop() {

  DigiKeyboard.update();

  if (digitalRead(1) == LOW) {

    DigiKeyboard.sendKeyStroke(KEY_ENTER);

    DigiKeyboard.delay(300);

  }

}

This capability enables macro pads, automated login devices, accessibility tools, and yes—security testing devices similar to the USB Rubber Ducky.

Common Project Categories

Project Type	Description	Difficulty
USB Macro Pad	Programmable shortcut keys	Beginner
Password Manager	Auto-type stored credentials	Intermediate
LED Controller	WS2812 NeoPixel strips	Beginner
Sensor Logger	Temperature/humidity monitoring	Intermediate
USB Volume Knob	Rotary encoder media control	Intermediate
BadUSB Clone	Security testing device	Advanced
OLED Display	I2C display with tiny graphics	Advanced
Servo Controller	Single servo projects	Beginner

Working with I2C Devices

The ATtiny85 lacks dedicated I2C hardware but supports it through USI (Universal Serial Interface). Use the TinyWireM library instead of the standard Wire library:

#include <TinyWireM.h>

void setup() {

  TinyWireM.begin();

}

void loop() {

  TinyWireM.beginTransmission(0x3C);  // OLED address

  TinyWireM.write(0x00);

  TinyWireM.endTransmission();

}

Memory constraints make I2C OLED displays challenging. Standard Adafruit libraries won’t fit; use lightweight alternatives like Tiny4kOLED designed specifically for ATtiny85.

Troubleshooting Digispark ATtiny85 Issues

Common problems and their solutions:

Board Not Recognized

Symptom: No USB connection sound, device doesn’t appear in Device Manager.

Solutions:

• Reinstall drivers using administrator privileges
• Try different USB ports (USB 2.0 often works better than USB 3.0)
• Check if the board is a defective clone
• On Linux, verify udev rules are configured

Upload Timeout

Symptom: “Device search timed out” or similar message.

Solutions:

• Unplug the board before clicking Upload
• Insert within the 60-second window after the prompt appears
• Try plugging directly into the motherboard rather than through a hub
• Some clones require longer detection time—wait a moment after plugging in

Sketch Runs Once Then Fails

Symptom: Code works after upload but not after power cycling.

Solutions:

• Add DigiKeyboard.update() or DigiKeyboard.delay(5000) at sketch start
• The bootloader needs time before your sketch hijacks USB pins
• Avoid immediate USB communication in setup()

P5 Doesn’t Work as I/O

Symptom: Pin P5 shows unexpected behavior or only outputs 3V.

Cause: Most clones keep P5 as the reset pin rather than disabling it.

Solution: Modify fuse settings (advanced, irreversible without high-voltage programmer) or design around using only P0-P4.

Digispark ATtiny85 Resources and Downloads

Resource	Description	Link/Location
ATtiny85 Datasheet	Official Microchip documentation	Microchip website
Digistump Board Files	Arduino IDE board definitions	GitHub digistump repo
Windows Drivers	libusb-win32 drivers	GitHub releases
Micronucleus Bootloader	USB bootloader source	GitHub micronucleus
DigiKeyboard Library	HID keyboard emulation	Included with board package
TinyWireM Library	I2C for ATtiny	Arduino Library Manager
Tiny4kOLED Library	Lightweight OLED driver	Arduino Library Manager
DigiSpark Scripts	USB automation examples	GitHub community repos

Frequently Asked Questions About Digispark ATtiny85

Can the Digispark ATtiny85 replace an Arduino Uno?

No, but it can replace an Uno in specific applications. If your project needs only a few I/O pins, fits within 6KB of code, and doesn’t require hardware serial or extensive libraries, the Digispark ATtiny85 works beautifully. Complex projects with multiple sensors, displays, and communication interfaces still need more capable boards.

Why does my Digispark ATtiny85 take 5 seconds to start?

The Micronucleus bootloader waits approximately 5 seconds after power-up, listening for programming commands over USB. If none arrive, it transfers control to your sketch. This delay ensures you can always reprogram the board, even if your sketch crashes immediately or disables USB functionality.

How do I use Serial.print() for debugging on Digispark ATtiny85?

Traditional serial debugging isn’t available since the ATtiny85 lacks hardware UART and USB communication is software-based. Alternatives include: blinking the onboard LED in patterns, using DigiUSB library for software serial over USB, or connecting an I2C OLED for visual feedback.

Is the Digispark ATtiny85 safe for USB HID projects?

The hardware itself is safe—it’s just a microcontroller. However, keyboard emulation capabilities can be misused. Never deploy HID scripts on computers you don’t own or have permission to test. Many organizations consider unauthorized USB HID devices security threats and may flag or confiscate them.

What’s the difference between genuine Digispark and clones?

Original Digisparks came from Digistump (now defunct). Clones vary in quality and may have different revision numbers, LED locations, or P5 functionality. Most $1-2 boards from AliExpress or eBay are Rev 3 clones that work identically for most purposes but limit P5 to reset functionality only.

Conclusion

The Digispark ATtiny85 occupies a unique position in the maker ecosystem. It’s not trying to compete with Arduino Uno on features—it’s enabling projects that wouldn’t exist otherwise. When you need a tiny, cheap, USB-programmable microcontroller that fits anywhere and costs almost nothing, nothing else comes close.

I keep a handful of these boards in my parts drawer at all times. They’re perfect for quick USB automation tools, tiny sensor nodes, LED controllers, and proof-of-concept prototypes. The limitations are real—512 bytes of RAM disappears fast, and some libraries simply won’t fit—but working within constraints often leads to more elegant solutions.

Whether you’re building a custom macro pad, creating a USB prank device, or learning microcontroller programming on a budget, the Digispark ATtiny85 delivers remarkable capability in an impossibly small package. At this price point, you can afford to experiment freely and discover what this tiny board can really do.

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Note: The microcontroller is the ATtiny85, not ATtiny86. There is no ATtiny86 chip—this is a common misconception. Always verify you’re purchasing ATtiny85-based Digispark boards.

Last updated: January 2026