ESP32 + SSD1306 OLED I²C
ESP32 DevKit driving a 128×64 OLED display over I²C — four wires (3V3 / GND / SDA / SCL). The standard "first display" project for ESP32 learners.
For the ESP32 / IoT learner
The SSD1306 OLED is the canonical first display project for an ESP32. Four wires get a 128×64 pixel monochrome display running over I²C. Two things differ from the equivalent Arduino Uno setup:
3.3 V supply, not 5 V. The ESP32 runs at 3.3 V on every pin including its supply rail. Wiring an OLED to the Uno's 5 V will work, but mixing in 5 V signals from a Uno into the same I²C bus as the ESP32 will damage the ESP32. Stay on the 3V3 rail.
Default I²C pins are GPIO21 (SDA) and GPIO22 (SCL). The Adafruit / Espressif convention is green for SDA and white for SCL — preserved here. These pins are remappable in firmware via Wire.begin(sda, scl) if you need them elsewhere.