This digital alarm clock displays the time on a 4-digit 7-segment display. It has the following features:

• Two buttons for setting the current time (Hour / Minute)
• Programable alarm with a snooze function
• The alarm sound can be easily customized in code, and even play melodies
• The colon symbol blinks to indicate seconds
• Optional RTC to make the clock more accurate
• Power loss recovery: current time and alarm settings are stored in RTC

To set the time, press the Minute/Hour buttons.

Pressing the Alarm button enables/disables the alarm. The screen will display the alarm state by showing the word "on" or "off".

After enabling the alarm, the current alarm time will be displayed for a few seconds. You can use the Minute/Hour buttons to adjust the alarm time. To finish, press the Alarm button again, or just wait a few seconds.

When the alarm goes off, press the Alarm button briefly to snooze it for 9 minutes. The screen will display four circles to let you know that the alarm was snoozed.

To stop the alarm, hold down the Alarm button for one second or more.

The code is divided into several modules:

1. config.h - Configuration options for the clock: whether to use an RTC chip, Snooze time, and more. Using a configuration file a common practice when you have several modules in your program.
2. alarm-clock.ino - The main program code. It manages the user interface: the 7-segment display and the buttons.
3. Clock - The Clock class manages the current time and the alarm state machine. It uses the RTClib library to communicate with the RTC chip and track time.
4. AlarmTone - The AlarmTone class play the alarm sound. You can change the values of the TONES array, TONE_TIME and TONE_SPACING to customize the alarm and play different tones and melodies.

• You can also use a Common Cathode 7-segment display, just adjust the DISPLAY_TYPE constant in config.h, and switch to NPN transistors.

To keep the clock hardware down to minimum, the Arduino controls the 7-Segment display directly, using the SevSeg library. This approach has a downside, however: it uses 12 GPIO pins!

If you want to save on Arduino pins, you can use a 74HC595 shift register to cut the pin usage down to 6, or even a 7-Segment display with an integrated controller chip, such as TM1637, HT16K33, or MAX7219. In this case, you will need to change the code to use a different display library (SevSeg does not support this case), but this is out of the scope of this project.

• The pin numbers for your 7-segment display may differ. Please consult the datasheet relevant to your device to find out the relevant pin numbers.