You can technically make a clock using only the Metro Mini and the display, but the clock would need to be re-set every time it looses power or is reset. It also isn't super accurate. That's where the real-time clock module comes in. It has a coin cell battery backup, and is a much more accurate timekeeper than the crystal onboard the Metro Mini.
Next, place the three boards onto the breadboard as seen in the diagram above.
Both the RTC module and the display can communicate with the Metro Mini over the I2C protocol, so there are only two pins for needed to connect them all for communications. Grab a breadboard, and then wire them this way:
- Metro Mini pin A4 to RTC SDA to display SDA
- Metro Mini pin A5 to RTC SCL to display SCL
The other wiring needed is common ground and 5V power among them all. Wire this:
- Metro Mini 5V to RTC Vin to display +
- Metro Mini GND to RTC GND to display -