David Johnson-Davies published another great mini project. It’s a Timer based on ATtiny402 and was build to demonstrate the low power sleep mode of the microcontroller.
This article describes how to use the new 0-series and 1-series ATtiny microcontrollers in low-power projects, taking advantage of sleep mode to maximise the battery life and avoid the need for an on/off switch. The project is a simple 15-minute timer that flashes an LED once every 2 seconds while it is counting down, and then beeps a piezo buzzer when the time has expired. You could use it as the basis for an egg timer, a bath-overflow alarm, or any other fixed timer application.
ATtiny402 Timer with low power sleep mode – [Link]