The circuit contains a few basic elements, an flip-flop based oscillator, a set of delays, a flip-flop as a sensor, and the audible alarm.The circuit consists of three parts : oscillator ,sensor and audible driver.

The length of the sleep cycle varies for each person, and averages about 90 minutes. I wanted to try to measure the length of mine, without having to wake up and check a clock. I also wanted to get an idea of how much I naturally move around during the night, and what patterns I might find therein.