Propeller Clock on a Mirror.


Description of this clock.

Mechanically scanned display

The display of this clock not like any other clock. This clock uses a mechanically scanned display.

In a scanned display the lights, LEDs, or what ever makes visible dots, are not on all the time. The leds turn on and off, one after another, very rapidly. Due to the slow response of the human eye we get the impression that the lights are on all together and we can read the display.

Scanning in this clock is mechanically. A limited number of leds are placed in a row and attached to a rotating arm. The arm spins at 1500rpm (or more) and the leds are turned on and off at very precise times and places. This gives the impression that there are several hundred leds making up a complete display. The fact that the arm is spinning at 1500rpm the leds, the electronics and the arm itself are hardly visible. All we can see are the lighted dots from the leds making a readable display that seems to float.

Depending on the form of the arm, the display is either a cylinder (like Bobís original clock) or a disc. The cylinder shaped display can only show digits. With the disc shaped display it is also possible to simulate analog hands.


Settings the clock

Settings this clock is a tricky part. The electronics to drive the leds and to keep time are located on the rotating arm. Early versions used buttons on this arm. You had to start the clock to see the time, turn off the motor, push the buttons a number of times and re-start the motor to see the change. This has to be repeated until the time is correct..

Other designs use a reed-switch that can be actuated by holding a magnet near the rotating arm! Very tricky!

Chester used two leds, one visible light, one infrared, to create a two-button system. This made settings the time a lot easier.

But I wanted to display time AND date. To set time and date with just two buttons would not be very efficient. So I connected an infrared sensor to the CPU and programmed it to decode signals from a RC5 remote control. This opened up a lot more possibilities. The remote can be used to set time and date. It can also be used to set different display modes. In the future I plan to make it possible to send custom messages to the display. Maybe even little drawings.