Arduino 7-segment clock

This public ExoSynk project is a real Arduino Uno clock, not a blank demo. It uses four multiplexed common-cathode 7-segment displays to show 24-hour time in HH:MM format.

Wiring

• D2-D8 drive the shared segment bus for a through g.
• D9-D12 switch the four digit commons through NPN transistors.
• A0 increments the hour.
• A1 increments the minute.
• The buttons use 10k pull-ups to 5V, so the inputs stay stable.

How it works

The sketch keeps time with millis(), updates the clock once per second, and multiplexes one digit at a time so the Arduino only needs 11 output pins. If you press the hour or minute button, the display nudges the time forward.

What to try

1. Run the sketch and watch it count forward in 24-hour mode.
2. Tap the hour button a few times and set a different time.
3. Tap the minute button until the display rolls from 23:59 to 00:00.
4. Fork the lab and turn it into an alarm clock, timer, or countdown display.

Notes

This version intentionally uses a standard 7-segment layout and a normal Arduino sketch, so it stays editable inside ExoSynk instead of being a fixed mockup.