CONNECTING A 0.91” OLED DISPLAY TO THE ATTINY85

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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:
Arduino UnoATtiny85
Pin 10RESET
Pin 11MOSI (PB0)
Pin 12MISO (PB1)
Pin 13SCK (PB2)
5VVCC
GNDGND

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

  1. 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.
  2. Board Settings:
    • Tools → Board: “ATtiny25/45/85”
    • Processor: “ATtiny85”
    • Clock: “8 MHz (internal)”
    • Programmer: “Arduino as ISP”
  3. Burn Bootloader:
    Tools → Burn Bootloader
  4. Upload Sketches:
    Use Upload using Programmer (Shift + Upload icon)

Connecting the OLED Display (128×32, 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: 128×32 pixels
  • Interface: I2C
  • Operating voltage: 3.3V–5V
  • Pins: VCC, GND, SCL, SDA

ATtiny85 Pinout

PinFunction
1 (PB5)Reset (or GPIO)
2 (PB3)GPIO3 / ADC3
3 (PB4)GPIO4 / ADC2 / SCL
4GND
5 (PB0)GPIO0 / MOSI / SDA
6 (PB1)GPIO1 / MISO
7 (PB2)GPIO2 / SCK
8VCC

I2C Connection

OLED DisplayATtiny85
VCCVCC (Pin 8)
GNDGND (Pin 4)
SCLPB2 (Pin 7)
SDAPB0 (Pin 5)

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 128×32 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

FunctionPinNotes
SDAPB0 (5)Use TinyWireM
SCLPB2 (7)Use TinyWireM
Power VCCPin 82.7V–5.5V (3V ideal)
Power GNDPin 4Connect to ground
Display driverSSD1306Compatible with Tiny4kOLED
I2C libraryTinyWireMBit-banged implementation

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!

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