This is a really coool project from they had the idea of creating a clock in such a way: make a red, a green and a blue ‘hand’ and by lighting up the three dies of an RGB-led, you can control exactly at what angle the image of every hand shows up. Apart from the hands, the fan itself doesn’t need to be modified: the led, in conjunction with a microcontroller, does all the work.

picture of the fan for led clock

This is the fan itself. I glued three pieces of paper to it and used a felt tipped pen to colour them in: red for the hour hand, green for the minute hand and blue for the second hand. Eventually, I remove the blue piece: it wasn’t colored in completely OK and the green piece reflected enough blue to give an indication of where the hand indicating the seconds is. Btw: The angle you put the hands in isn’t inportant: the software can compensate for any decision you make when you initialize the hardware.
The software mainly works by using three interrupts: the first one kicks in 500 times a second and is used for button debouncing and keeping time. The second one is dynamically adjusted to kick in 60 times per rotation of the fan and handles the showing of the hands by enabling and disabling the three colors of the RGB-led. The third one kicks in every time the fan generates an RPM-pulse. When that happens, the microcontroller will evaluate the speed at which the rotation-timer happens and adjust it when necessary. The software for the clock is written in avr-gcc and released under the GPL v3, so if you want, you can modify it to display a clock on anything rotating quickly enough.

Watch the clock in action

If you like this project visit its page Link