A reader writes:

I live in Taiwan, and I just came across a new LED device which seems very cool.

First, here is a link. It's all in Chinese, unfortunately, and I can't read it to translate for you, but there are at least some photos to give you an idea.

'Aurora' LED sign

[Here's a goofy machine-translation, which gives the thing the name "Aurora", which sounds good enough to me. The price, 1699 Hong Kong dollars, is as I write this about $US220.]

Basically, this works like a Lite-Brite, but with LEDs. There is a black PCB, entirely pierced through with holes. It has no wires, and there are no visible electronic components except for the DC input at one corner. You can plug in LEDs on either side, front or back, in any pattern you like. It's powered by either a wall-wart, a small battery pack, or a USB power connector.

A friend of mine here showed it to me tonight, and it was very impressive. Water-resistant, even - he poured a beer all over both sides of one with many lit LEDs, and there was nary a flicker.

Anyway, if you're interested, I could probably find out more about it.


I immediately, and completely wrongly, picked the Aurora as a cheaper clone of the Bandai Luminodot (dodgy translation), which was all the rage on the gadget blogs a few months ago. Some hipster has presumably bought himself a Luminodot for $US200 delivered on eBay by now, but I sure ain't.

Doug was quick to point out, though, that this thing is not a backlit-plastic-pegs device like the Lite-Brite or Luminodot, but a bunch of little powered breadboard-ish holes, into which you can plug as many or as few LEDs of whatever colour you like, and have 'em all Just Work with no fooling around with supply voltages or current-limiting resistors or fancy driver pucks.

(I think a cheaper version of the Bandai doodad might be makeable with a laptop CCFL backlight panel and little black shutters that open to let light out when you push a peg though them. Or you could do it the Lite-Brite way, and put a new sheet of black paper over the light for the pegs to puncture every time you want to make a new picture.)

Undaunted, I immediately developed total certainty regarding the Aurora's similarity to another light-array gadget.

Peggy 2.0

That gadget is the open-source "Peggy" invented by Evil Mad Scientist Labs, which is now up to version 2, and available as a kit.

The different Peggy versions are capable of various kinds of animation, and can even be used to display (very low-res) video.

The array Doug saw may, like the Peggy, only actually light one row or column of LEDs at a time, but cycle through them too fast for any flicker to be visible. (It may or may not do the same devious multiplexing as the Peggy, and is almost certainly a lot less "hackable".)

The Aurora is clearly being promoted as being useful for commercial signage, as an alternative to the custom-made, ultra-bright LED-array signs that I've seen sprouting around the place.

Doug was under the impression that the retail price "for a board about a foot square" was only around $US30, plus another $US10 for the power supply. That'd make it worth buying just for the amusement value, but doesn't line up with the $HK1699, $US220-ish price on the product page.

Never mind, though; when an odd toy starts being sold on any Web site ending in .tw, its price will probably be in free-fall soon.

13 Responses to “LED-Brite”

  1. xuth Says:

    One should avoid leaving these things laying around Boston for fear that the Boston police make a big deal about it.

  2. solipsistnation Says:

    I'm currently designing and am about to build an RGB Peggy clone, based partly on Peggy 2 and partly on the Meggy Jr. RGB kit from the same guys, which is very very awesome...

    Assuming I can get the multiplexing fast enough using an arduino CPU, it should be very cool.

  3. peridot Says:

    If they're all illuminated all the time, then there's no reason for it to be multiplexed, is there? You just have a bag full of LED-plus-resistor units with two dissimilar pegs, and an array of holes for them to fit into. Or, better, you build a tiny phono-jack-like connector on the back of each LED-plus-resistor, so that you just plug it in anywhere. Then all you need is a power supply - just the wall wart - and no other electronics.

    Unfortunately, this will make it a pain to build such a gadget at home, since making zillions of the little LED units is going to be tiresome, as is making the board to plug them into.

  4. FuzzyPlushroom Says:

    I'm feeling some awesome Connection Machine influence here.

  5. Changes Says:

    How exactly does the device work? Does it actually have a tiny power supply and/or current regulator behind each LED? It seems hard to believe, but I can see no other way in which it could manage a series/parallel connection of LEDs without knowing which is which and without burning some up and underdriving others...

  6. solipsistnation Says:

    Oh, you know. Peggy and Peggy2 aren't charlieplexed-- they're for-real multiplexed using a couple of LED driver ICs and a couple of 4-to-16 demultiplexers.

    Charlieplexing does look cool, but Peggy is a little more complex than that.

  7. peridot Says:

    Changes, all you have to do to light up a bunch of LEDs is attach an appropriate resistor to each and then feed them all from the same V+ and ground. If you want different colors the V+ will have to be high enough for the bluest color (where white is actually UV) and so it'll be a little less efficient, but a resistor per LED is cheap.

    Alternatively, if you multiplex it so only one is lit at a time, you can have one resistor/constant-surrent supply for many LEDs. But if they're all going to be on all the time this seems unnecessarily complicated.

  8. Changes Says:

    I'm aware of the resistor thing, but I understand what you're plugging in that board are bare unresistored LEDs.

  9. mangoman Says:

    Changes, it wouldn't be a big deal to have a resistor per LED on the board. For a 20x50 position board (1000 LEDs), and a per-resistor price of $AU0.004, that's a per-board cost of $4. You'd simply have the top plane of the PCB V+, the bottom GND, and one resistor to to either the anode or cathode of each LED.

  10. TwoHedWlf Says:

    What's the per board cost of an extra 2000 solder joints?

  11. mangoman Says:

    I couldn't say with certainty, but for a reflow-soldered board the extra (time, and therefore money) cost would be in the pick-and-place for the extra components rather than the soldering (as the joints are all formed in one pass). There's presumably some sort of socket being placed for each LED already, so the extra cost is doubling the number of component placements.

  12. Changes Says:

    But you can't just have a resistor for each LED slot. LEDs of different colors use different resistors.
    The only way I can see this working is with a current-regulated supply for each LED. It could just be flickering them really fast in order to use one power supply for several LEDs, but just resistors on the board won't do if you have to be able to plug different colours of LEDs in the same slot and have them work fine.

  13. mangoman Says:

    Actually you can, you just can't be quite as fussy about efficiency. For example, take a red LED with a forward voltage (V_f) of ~1.5V, and a blue LED dropping ~3.0V. Wire them in parallel, each via. a separate 200Ohm resistor from 4.5V. The red is sinking (4.5-1.5)/200 = 15mA, and the blue is sinking 7.5mA, half as much. But since the forward voltage for the blue is twice as high, the power (P=VI) is the same: 22.5mW. An LED with a V_f in between (say, a green one) will dissipate slightly more (maximum 25.3mW @ V_f=2.25V). The cost is that the red LEDs will only be ~33% efficient, 2/3 of the applied power is dissipated in the dropping resistor. A board fully populated with 1000 red LEDs will be supplying 25W to produce light, and wasting 50W in the dropping resistors. For blue it'll be 25W LEDs, 12.5W resistors. Anyway, it's totally possible, just not particularly efficient. Cheap though, and for business signs, I don't imagine the boards will be more than 10-20% populated.

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