PROJECT CLOCK // I2C OVERVIEW

Component List & Sourcing

• **OLED 0.91" Display** (I2C Protocol)
• **Arduino Nano** (V3 or compatible)
• **RTC DS3231 Module**
• Jumper Wires and PCB/Breadboard
• **Estimated Total Cost: 18,90 €** (Updated to include RTC)

I2C Wiring Matrix

I2C uses only two data lines (SDA/SCL) plus power. Multiple I2C devices (like the OLED and RTC) **share** these four pins by connecting them in parallel.

**GND** (Grey) → **GND** (OLED, RTC)
**5V** (Red) → **VCC** (OLED, RTC)
**A5** (Blue) → **SCL** (OLED, RTC)
**A4** (Green) → **SDA** (OLED, RTC)

Core Code Snippet (RTC Clock)

This code reads the time from the RTC module and displays it on the OLED. Libraries needed: **Wire, RTClib, Adafruit\_GFX, Adafruit\_SSD1306**.

#include <Wire.h>
#include <RTClib.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

RTC_DS3231 rtc;
Adafruit_SSD1306 display(128, 64, &Wire);

void setup() {
  Wire.begin();
  
  // Check if RTC is available and running
  if (! rtc.begin()) {
    // Optionally display an error message here
  }

  // Zeit einmalig setzen (danach auskommentieren!)
  // rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));

  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
}

void loop() {
  DateTime now = rtc.now();

  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(0, 20);

  // HH:MM:SS
  if (now.hour() < 10) display.print("0");
  display.print(now.hour());
  display.print(":");

  if (now.minute() < 10) display.print("0");
  display.print(now.minute());
  display.print(":");

  if (now.second() < 10) display.print("0");
  display.print(now.second());

  display.display();
  delay(500);
}