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TIA wiki user D18c7db contributed this wonderful guide for the Fantazein moving wand clock. He describes its function and even created a circuit diagram for it!
Check it out after the jump.
This is a Fantazein moving wand clock, the type that creates the illusion that text floats in midair as seen in the small picture below.
This guide is not so much on how to take the clock apart which is trivial. Just remove the two screws in the metal baseplate and the two halves of the plastic case come apart. This is more of a guide of what’s inside.
With that in mind, the picture below shows the front of the circuit board assembly with the battery holder and the programming keypad. The wand with 8 red LED can be seen protruding from the top. This wand moves at about 12 oscillations per second becoming almost invisible to the eye while the LEDs flash creating a floating text effect.
Below is the back of the circuit board. The large chip is an Atmel AT87F52 microcontroller that is the brains of the whole clock. In the middle are two flat iron bars spaced apart with coils wound onto them. The two coils are wound in series and are pulsed on and off by the microcontroller. A permanent magnet affixed to the wand creates a repulsive force when the coil is activated pushing the wand slightly to one side.
Since the coil can only be turned on or off and the polarity is not reversed, the repulsive force on the wand is always in the same direction. The wand is held in place through a springy thin steel blade which is firmly affixed to the L shaped aluminium mound bolted to the circuit board. The springy steel blade has a strong tendency to return the wand to the vertical position. By pulsing the coil on and off an oscillation is induced in the wand which initially only moves back and forth a little but as the coil is pulsed the oscillation becomes wider.
Think of is a a swing. As you lean back you swing only a little but as you keep leaning back and forth at the right time you increase your swing arc significantly.
The side view below of the circuit board shows the coil assembly as well as the wand with the permanent magnet. An aluminium bar is mounted to the wand which passes between an LED and a photodetector as the wand swings. This is used by the microcontroller as a feedback mechanism to detect the wand swing and time the coil pulse timing and duration accordingly.
Closeup view of the semiconductors below. The large chip is the microcontroller, to the left of it as a LM339 quad op-amp. Above the micro is a LS244 driver and to the right of that a small 93C56 EEPROM.
Finally below is a hand drawn reverse engineered circuit diagram of the whole clock. The schematic is elegant in it’s simplicity. The micro is read protected and the firmware could not be read however since it’s socketed, a new micro could be fitted and given enough skill one could develop a replacement firmware code. I started doing that and got as far a creating a sustained wand movement that would recover if the wand was stopped by an obstacle such as your hand but other more pressing matters put this project on the backburner.
