0.91-inch OLED Display on an ATtiny85

The ATtiny85 is a compact and low-power microcontroller ideal for minimalist electronics. Whether you’re building a wearable, a sensor node, or a creative display, the ATtiny85 paired with a 0.91” OLED display delivers powerful functionality in an ultra-tiny footprint. In this guide, you’ll learn how to flash the ATtiny85, wire it up to an OLED display, and power it from a CR2032 battery.

What is the ATtiny85?

Minimalist MCU:
The ATtiny85 is an 8-bit microcontroller from Atmel (now Microchip) with 8KB flash, 512B SRAM, and 6 GPIO pins. It’s programmable via Arduino and ideal for low-power, space-constrained projects.

Features:

• 8-bit AVR RISC architecture
• Up to 20MHz clock speed (internal oscillator)
• 5 I/O pins (plus reset)
• I2C, SPI (via USI), ADC, PWM support
• Extremely low power consumption
• DIP-8 or SMD form factor

Flashing the ATTiny85 using an Arduino

Before connecting the OLED, the ATTiny85 must be programmed. You can do this using an Arduino Uno as an ISP (In-System Programmer).

Hardware Needed

• Arduino Uno
• ATtiny85 (DIP-8)
• Breadboard + jumper wires
• 10µF capacitor
• Arduino IDE installed

Steps

1. Setup Arduino as ISP:
   • Open the Arduino IDE.
   • Load File > Examples > 11.ArduinoISP > ArduinoISP.
   • Upload to your Arduino Uno.
2. Connect the ATtiny85:

Note: Don’t forget to place a 10µF capacitor between RESET and GND on the Uno to disable auto-reset.

3. Install ATtiny Board Support:
   • Arduino IDE → Preferences → Additional Board URLs:
     https://raw.githubusercontent.com/damellis/attiny/ide-1.6.x-boards-manager/package_damellis_attiny_index.json
   • Boards Manager → Install ATtiny by David A. Mellis.
4. Board Settings:
   • Tools → Board: “ATtiny25/45/85”
   • Processor: “ATtiny85”
   • Clock: “8 MHz (internal)”
   • Programmer: “Arduino as ISP”
5. Burn Bootloader:
   Tools → Burn Bootloader
6. Upload Sketches:
   Use Upload using Programmer (Shift + Upload icon)

Connecting the OLED Display (128x32, I2C)

This display uses the SSD1306 driver and communicates via I2C. It's a perfect fit for ATtiny85 thanks to its small size and low power usage.

Display Specs

• Resolution: 128x32 pixels
• Interface: I2C
• Operating voltage: 3.3V–5V
• Pins: VCC, GND, SCL, SDA

ATtiny85 Pinout

I2C Connection

Note: I2C on ATtiny85 uses Software I2C (bit-banged). Libraries like TinyWireM or Adafruit_SSD1306 + TinyWireM support this.

Powering with a CR2032 Battery

To make the project portable, we’ll power it using a 3V CR2032 coin cell.

Power Tips

• Connect CR2032 + to VCC, to GND
• Use a low-dropout voltage regulator if running peripherals at 3.3V with stable output
• Keep code optimized to minimize power draw
• Use sleep modes to extend battery life

Required Libraries (Arduino IDE)

#include <TinyWireM.h>#include <Tiny4kOLED.h>

Install these via the Library Manager or GitHub.
TinyWireM emuleert I2C op de ATtiny85, en Tiny4kOLED ondersteunt de SSD1306 128x32 displays.

Display Example: StudioPieters Project (Centered Text)

#include <TinyWireM.h>#include <Tiny4kOLED.h>void setup() {  TinyWireM.begin();        // Initialize I2C  oled.begin();             // Initialize OLED display  oled.clear();             // Clear the screen  oled.setFont(FONT8X16);   // Use 8x16 font  oled.on();                // Turn on the display  // Line 1 (Y = 1)  oled.setCursorCentered(1);  oled.print(F("StudioPieters"));  // Line 2 (Y = 2)  oled.setCursorCentered(2);  oled.print(F("ATTiny85 - OLED (I2C"));  // Line 3 (Y = 3)  oled.setCursorCentered(3);  oled.print(F("Project"));}void loop() {  // Static display, no refresh needed}

ATtiny85 OLED Quick Reference

Best Practices and Common Mistakes

• Don’t use hardware Wire.h , use TinyWireM for I2C on ATtiny.
• Keep OLED update rate low to conserve battery.
• Pull-up resistors on SDA/SCL are usually not needed (OLED module includes them).
• Don’t exceed CR2032 max current draw (~20mA continuous).
• Use sleep_mode() in loop() to save power.
• Mind ATtiny85 memory limitations (only 8KB flash).

Conclusion: Tiny MCU, Big Possibilities

The ATtiny85 + OLED combo is a powerful foundation for compact, battery-powered display projects. Whether you’re creating a branding badge, a sensor output monitor, or a creative wearable, this minimalist design packs a surprising punch.

Mastering the connection between the ATtiny85 and OLED unlocks a new tier of low-power, display-driven innovation, perfect for the maker who believes less is more.

Happy Building!