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.