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RobG

RGB Globe

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I just came across this project and it is so awesome, I have to make one like that for my kids :)

Unlike SolderLab guys, I will not use wires, I will use PCBs as a frame.

Here are my few initial ideas:

1. Create 1" x 2" boards, contacts on both ends, 5050 or 5mm LEDs, chips on the bottom.

2. Create circular boards out of 4" boards, 1/4, 1/6, or 1/8 circle. 5mm LEDs.

I think I will go for 2nd option since it's easier to assemble.

Each segment will have 16 LEDs, 6 chips, few caps, and possibly place for MCU and IR detector, so no additional boards will be required.

Also, I will use TLC series chips because they have constant current outputs, more current, less resistors, less soldering.

BTW, SolderLabs' GlobeSimulator software is available for free!

 

 

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Very cool, Rob. Definitely going on my list of "cool projects to try some day".

 

Will the speed be slow enough to prevent the (unsupported) top of your board from pulling outward, exerting leverage on the connection point on the bottom? If I may humbly suggest, a solder pad at the top-left of the control board and one at the end of the upper board would provide points to anchor some (taut) medium-thickness magnet wire to provide a little support without detracting much visually (could double as a conductor, if you need it for something).

 

Just my $0.02, please see my sig for cautions. ;)

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The wire idea is good, I will add extra solder points. You can also complete the circle with empty or populated boards and add top support. I will start with half circle and bottom only and see what happens.

I am almost done with the board, have to clean up the tracks, the size is 7.4" dia., 60 deg.

There are 16 5mm RGB common anode LEDs, 6 TLC5916's, 6 resistors, and 6 caps.

Yes, TLC5916 are pricier, but they are high current (compared to 595) and do not require resistors for each LED (595 would require 48 resistors per board, that's 144 per set!)

3 boards are needed for a half circle, that's 48 LEDs.

You can get 3 sets when ordering 10cm x 10cm PCBs from Seeed.

 

UPDATE:

Now when I have my "papertype," I am wondering if this thing is too small.

 

 

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After few more versions, settled on the final two designs.

First one has 7.4" diameter, second has 9", 60 degree pieces.

Both have 16 LEDs and three TLC59281s per segment.

TLC59281(SSOP) is the cheapest option compared to versions with TLC5916(SOIC) or TLC5952(TSSOP.)

 

BTW, trying to decide if I should use clear or diffused LEDs. Diffused would look better from all angles, but clear ones would make nice projections on the walls. Maybe I should assemble the whole circle and have diffused on one side and clear on the other :)

 

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I sometimes wonder why there isn't 2 boards in these designs... both with double sided leds all slightly off of each other so there's less of a "line" pattern in the spin. The extra components required can be put in the center area.

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I sometimes wonder why there isn't 2 boards in these designs... both with double sided leds all slightly off of each other so there's less of a "line" pattern in the spin. The extra components required can be put in the center area.

That sounds like a very good way to increase resolution!

One could even use a 24" or 28" bicycle wheel (rim) without all the spokes mounted on top of a brushless motor, and one of these addressable LED strips where each LED has its own controller and communicates over OneWire.

Could be the largest LED globe atm :D

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That sounds like a very good way to increase resolution!

One could even use a 24" or 28" bicycle wheel (rim) without all the spokes mounted on top of a brushless motor, and one of these addressable LED strips where each LED has its own controller and communicates over OneWire.

Could be the largest LED globe atm :grin:

That would be amazing to see! 28" rim = about 3m of RGB strip, right? For the high-density strip, that's about 180 LEDs!

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Unfortunately, LED strip is not going to work, it's too slow. It takes ~60us to update each LED (~30us in fast mode, but I believe those strips are configured to use slow speed,) so to update 180 LEDs you would need 10.8ms.

 

For comparison, TLC59281 has 35MHz data transfer rate, which means you can update (in theory and @16MHz) 180 LEDs in just 270us, so @3600rpm, you can get 60 vertical lines per rotation (120 lines if the strip is all around.)

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how about mounting such a project in an up turned fish bowl like white opaque globe so that the image was (diffusely) projected onto its inner surface? if you could get the distance/intensity/focus right... smoke filled clear globe maybe? what if the globe were an opaque balloon kept inflated by the smoke?

 

kinda like a plasma globe...

 

Plasmalamp.gif

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