Like many parents, [Mike Tsao] is plagued by his kids’ urge to rise like the dead long before he’s ready to wake up. In an effort to preserve sanity, he built this clock to let the young ones know when it’s okay to get out of bed. Fittingly, he calls it the OK-Wake.
You may notice that the clock doesn’t have a display. That’s because his children are still too young to tell time (this is the foundation for needing a custom clock). Instead, that LED acts as the feedback. At night it will be off. Starting ninety minutes before it’s time to wake the LED will begin to pulse red, increasing in frequency as the target time approaches. When it’s okay to get out of bed the LED turns green and exhibits a pleasant “breathing” behaviour.
An ATtiny25 drives the device, along with an RTC chip. The single button is used to set the alarm. Actual time doesn’t really matter at all. Instead, the button just sets the alarm for twelve hours from when it’s pressed.