Shows the time and date, both local time and well as UTC. CET is provided with automatic summer/winter time. You can change this in the source code. See the Time library for details.
Uses the GPZDA field from the GPS. Although this is not officially supported or mentioned in the datasheet for MTK3339, it works very well. The program will not work on GPSs that don't emit GPZDA.
The program has been made for a 3.3V Arduino Pro Mini (Atmega 328P), but it's generic enough that it should work with many other microcontrollers. It only needs a serial port and i2c.
Make sure the voltage is compatible. Pro Minis seem to come in both 3.3V and 5V versions, while the GPS and display are for 3.3V.
| GPS | Pro Mini |
|---|---|
| VCC | VCC |
| GND | GND |
| TX | RX |
| RX | TX |
| OLED | Pro Mini |
|---|---|
| VCC | VCC |
| GND | GND |
| SCL | A5 |
| SDA | A4 |
Unfortunately the i2c pins (A4/SDA and A5/SCL) are not exposed on breadboard friendly pins. I suggest soldering a pair of headers on top of it.
Make sure to disconnect the GPS TX/RX when programming, otherwise data from the GPS will interfere with the programming process.
Because GPZDA gives us everything we need for time. Nothing less, nothing more. That makes the clock more power efficient and easy to work with.
And to my understanding the time is provided from the internal RTC clock, regardless of satellite availability. Even if the GPS is turned off, its internal clock keeps ticking, powered by the backup battery. That said, this retention doesn't seem to last for long, only a few hours or days.