power for POV display

Question

I want to build a litle POV display, but I didn't get how the power (and if possible a communication line) are transmited to the spinning part.

I've looked at some POV project but they usualy doesn't explain that part a lot...

Answer 1

You need to use some form of Slip Rings and carbon brushes. The Slip Rings are mounted on the spinning shaft which are a ring of brass that makes contact with sprung brushes that supply the power. They are similar to a commutator on a DC motor, except they are a continuous ring instead of segmented.

You'll need two Slip Rings for power and GND unless it's possible to use the shaft itself as GND, then you can get away with just one. But this would mean you'd need to mount all of your control circuitry on the spinning assembly, otherwise you'd also have to have extra rings to supply individual LED circuits.

A neat and cheap alternative to using carbon brushes is to use Tool Clips that are mounted on a piece of insulating nylon that surround the rings.

Answer 2

Here's some instructions on building a rather ingenious slip ring using ball bearings.

Answer 3

If you are building a small display, you can also do it with a round circuit board with circular traces that rotates coaxially with your rotating part with two fixed "brushes" (small brass springs) that each drag on one of the circular traces. Like a flattened out version of how a DC motor commutator works.

Answer 4

Please check out the list of POV displays. Many POV displays are "open-hardware" and so should have extensive documentation on exactly how their power and communications work -- if one doesn't have enough detail, try another one.

Nearly all POV displays that I've seen working use slip rings for power. (I've seen one working commercial POV display that uses an alternative to slip rings for power, and I plan to build a spinning POV display without slip rings that transfers power in a completely different way, but it's currently highly experimental). Power on the stationary side goes through the slip ring to a large capacitor (to ride out power glitches from bounces and non-conductive dirt in the slip ring) at typically 8 to 12 V, which supplies power to a voltage regulator that powers the microcontroller and the chips that apply power to the LEDs.

Many POV displays have no communication between the stationary part and the spinning part -- any user-interface buttons are on the spinning part, and you have to stop the motion, push the buttons (with a difficult-to-read linear LED array for feedback), then re-start the motion.

Some POV displays have a "communications" slip-ring or two for serial communication between the spinning part and the outside world. Alas, the slip ring adds glitches that are difficult to ignore.

Many POV displays have a Hall effect sensor on the rotor that passes a fixed magnet, so the spinning microcontroller can compensate for the actual rotational speed. In principle, one could send data from a stationary coil to a spinning Hall effect sensor near the rotational axis, but I haven't seen that actually working.

Some of them use infrared communication between the stationary part and the spinning part, much like IrDA or TV remote controls.