Project - Knock Clock
This project has recently appeared on the BBC TV show "QI XL" (Series N, Episode 11: "Nonsense").
This project is based on a project created at the Copenhagen Institute of Interaction Design Summer School. It's basically a clock with no display. You knock on the box, and it tells you the time back by knocking on the inside of the box.
The knocking mechanism in their version used a servo-motor which made a loud motor noise every time it knocked. I made a version using a quiet solenoid instead.
I basically used the same solenoid driving circuit as I used in my Twitter Drummer. When someone knocks it's detected by a piezo-electric transducer, and the time in hours and minutes is read from the ATmega168 microcontroller's built-in time functions. There's a software 'knock' function which is called the relavent number of times to represent hours, and then tens-of-minutes. The clock is accurate to the nearest ten minutes.
There are two buttons for setting the time, one for minutes and one for hours. You basically hold the button down until it knocks the correct number of times.
I'm currently making a completely new version of this, with better box and more accurate clock. The original was kind of thrown together, so I've taken a bit of time to get version two (V0.2?) as good as possible!