This Arduino-based Pomodoro timer project also uses this 25-minute cycle. Once you push the button to start the timer, it will run for 25 minutes, display a count-up timer and a "Study time!" ...

Finally, your Arduino toolkit will be incomplete if you don't purchase some sensor and circuit modules. After all, you can’t build a precise weather station without a BME280, DHT22, DS18B20, or ...