Forums > Technical Discussion > Luxeon Poi...

Posted: 9th Apr 2005
I didn't realize the voltage drop on the blue was that low. The voltage drop on many of of the high power blue LEDs I've seen is quite a bit higher. But even at 3.42 V you are cutting things really darn close if you aren't using a current limiter/current source. Here's the problem: Your dropping resistor is going to be so low that slight changes in battery voltage are going to have a dramatic effect on the current through the LED. And when you are pushing the drain rate on the Li-ion batteries as high as you are, you can expect quite a bit of voltage variation. Another thing to remember is that LEDs have a negative temperature coefficient. What this means is that as they heat up their resistance drops, which means they pass more current, and get hotter, and the resistance drops even more. (This is known as thermal runaway and is typically what kills LEDs that are wired in parallel without sufficient individual dropping resistors, BTW)

At this point I should probably interject that I'm not an EE, and all this is just stuff I learned in the process of building my own LED poi. I never expected it to get so complicated! And in fact, when I realized the level of complexity required to "do it right" the project stalled. I don't mean to scare you with any of this, I just want to try to save you some time, and perhaps you can pick up where I left off...

Now that said, and keeping in mind that I'm not a professional EE, here is how I would go about driving Luxeon poi: I would use two Li-ion cells in series to produce 7.2 volts. Putting the cells in series eliminates the problem of a stronger cell discharging through a weaker one. It also allows for more efficient regulator design, and I'd actually use for of them. A voltage regulator for the PIC and three current regulators, one for each LED. They would all be buck switching regulators, and you should be able to achieve close to 90% efficiency with a little bit of tweaking and careful component selection. I'm uncertain whether the constant-current regulators should be fixed and LED brightness set via PWM, or whether the LED brightness should be adjusted via adjusting the current setting on the constant-current regulators. I have read that green and blue LEDs are more efficient in terms of lumens/watt at lower current levels, and if this is true of the luxeons to a sufficient extent, you could potentially save quite a bit of battery power here. If you aren't doing PWM in the PIC, you run it at a much lower frequency and probably even put it to sleep which will save you even more power -- PIC power consumption is based largely on the frequency you run them at.

National (https://www.national.com/appinfo/power/) makes lots of regulators that will do a lot of what you want on a single chip, but unfortunately you can't get them in any format other than SMD.
One of the things that stalled my project was deciding whether to learn to solder SMD devices or whether to learn how to design my own switching regulators from discrete components -- both of which approach high art in terms of electronics.

As an aside, there isn't anything at all wrong with what you've been doing, and there is a hell of a lot to be said for having something working (I've just got a box of parts at this point) so keep on banging away at it! There is no substitute for having a working circuit to get some real measurements in terms of current draw and battery life -- after all, you'll have no idea of how much more efficient the more technical designs really are if you don't have a baseline to compare with. Keep up the work, and be sure to let us know how it goes!

-p.

Posted: 9th Apr 2005
I posted [url=https://www.homeofpoi.com/ubbthreads/showflat.php/Cat/0/Number/382143/page/0/view/collapsed/sb/5/o/all/fpart/1]a very short vid[url] of the slow colour fade over in the videos section if you're interested.

@Bird: The one I'm swinging there use 4xAA batteries. It weighs in at 150g which might sound heavy, but feels quite good to me. The cone of fabric slows them down a little, so I'm quite curious to see how well lighter ones will work.

@pj: Once again, some very good points. I've been wondering about the voltage drops, and I'm aware of pretty much everything you've pointed out there. I've been thinking about current sources and so forth for a while now, but it was less than a week ago that I finally understood that LEDs need current not voltage! I think I'd always ignored what I'd heard / read about it because I didn't quite understand it. I get it now

I'm by no means an EE either despite my degree being (supposedly) comprised 1/3rd of electronics! I've learnt considerably more by experimentation and by the many forums out here on the net. It's amazing how much you can learn by asking stupid questions I know what you mean about things suddenly getting very complicated. I've got that hamster bottle full of veroboard, AA batteries, luxeons and a little heatsink ...and it works ...but to get it to do all the stuff I have planned in my mind is another matter all together!

The PIC itself uses only a very tiny amount of power even at it's fastest settings - only a very tiny fraction of the Luxeons. You're right about higher frequencies drawing more, but still nothing to worry too much about. I suspect it wouldn't even need a regulator - just a direct feed from the batteries.

There's certainly a lot of experimentation I can do now to find optimum settings in terms of battery life etc.

The PWM is generated by the hardware, so running the PIC at 1Mhz shouldn't be an issue SMD is a bit of a pain, but it's certainly possible with a fine bit on the end of your soldering iron, a steady hand and a magnifying glass. My dad's got some solder-paste which I may investigate.

Thanks for the encouragement. I must admit, I stalled with this project for a looong time when I tried to get software PWM fast enough that you couldn't see it blinking. I found a new chip, got a new programmer and eventually got the two working to give me hardware PWM going. Once I had that working, I got a bi more interested again. Having something you can swing round your head is pretty rewarding

Cake or Death?

Posted: 9th Apr 2005
The first uC I started playing with was the Ubicom SX which is rated at 50 MHz, and can be pushed as high as 90 MHz. And executes most instructions in a single clock, whereas the PIC takes four. Suffice to say the little thing is a speed demon. ;-) That's why I've never had any problems with speed! But it sure does draw some serious current.

The SX-key (the programmer) also got me hooked onto ICSP/ICD, and when the Microchip ICD2 went on sale over Xmas, I popped for one.

In any case, I've been wanting to use much smaller batteries and much smaller LEDs,so the relative power requirements of the PIC do play a bigger part. I started toying with the idea of LED poi way back when the Sauce lights came out which are still pretty darn impressive given their puny LEDs, so I've just been wanting to make better Sauce lights, not something I can blind people with. ;-) You are absolutely correct that with the current draw of the Luxeons, the demands of the PIC are insignificant.

Given that, you could probably do all of the switching for the buck convertors right on the PIC and use the A->D as your current sense. Here are a bunch of URLs that I have bookmarked:

https://www.maxim-ic.com/appnotes.cfm/appnote_number/710

https://schmidt-walter.fbe.fh-darmstadt.de/smps_e/smps_e.html

https://www.national.com/appinfo/power/files/f3.pdf
https://www.national.com/appinfo/power/files/f4.pdf
https://www.national.com/appinfo/power/files/f5.pdf
https://www.national.com/appinfo/power/files/f6.pdf
https://www.national.com/appinfo/power/files/f7.pdf
https://www.national.com/appinfo/power/files/f8.pdf
https://www.national.com/appinfo/power/files/f9.pdf
https://www.national.com/appinfo/power/files/f10.pdf

https://atmel.com/dyn/resources/prod_documents/doc2542.pdf

Ponder... ponder... ponder...

I really need to dig out that project box and start playing again...

-p.

Posted: 10th Apr 2005
I think I may have just discovered the holy grail for my poi. Programmable current pump which works fomr an input voltage of 2.9 to 4.4v

Those processors sound pretty impressive - certainly a lot more advanced than the little PICs I've been toying with. Mind you, these seem ideally suited to the job!

After swinging my prototype around for a bit, I've started to think that making a much thinner cone might give a more impressive result. I also need to figure out a way of getting more light further up the cone - maybe some sort of lense would work. That, or using batwing (instead of lambartian) emitters and a reflector. Yet more possibilities to test out

Cake or Death?

Posted: 10th Apr 2005
That looks workable, but be sure to look at the "Efficiency vs. Vin" graph on page 4. That sharp discontinunity in efficiency based on source voltate and current draw looks like it's going to fall right where you'll be running the luxeons. Looks like if you aim right right for the peak you can manage 90% efficiency, but the supply voltage doesn't need to drop much for efficiency to fall below 60%. The other problem is that that chip is tiny -- it's small even as SMD components go.

The Ubicom SX is a very strange chip. It's actually based on the design of a rather old PIC, the 16C57 I believe. They just concentrated on making that old design run an blazing speeds.

-p.

Posted: 10th Apr 2005
One thing I forgot to mention... You don't need to use the fancy chips to get good efficiency. The chips just make the designs a lot easier and allow for fewer and less expensive external components. When you are making millions of something, this is a big deal. But for what we're doing, discrete components might be the way to go. Here are two circuits I dug out from my bookmarks:

https://www.romanblack.com/smps.htm

https://bobblick.com/3cell/

The first is a step-down and the second is step-up. They are both voltage regulators, but I don't believe it would be too difficult to convert them to current regulators.

-p.

Posted: 11th Apr 2005
real rainbow poi

they are pretty - keep at it hyperlight


cole. x

"i see you at 'dis cafe.
i come to 'dis cafe quite a lot myself.
they do porridge."
- tim westwood

Posted: 11th Apr 2005

Written by: pj

---

The chips just make the designs a lot easier and allow for fewer and less expensive external components. When you are making millions of something, this is a big deal. But for what we're doing, discrete components might be the way to go.

---

To be honest, the fact that you can get all-in-one chips was what was held my attention. If I had more of a grasp on how to go about constructing a current pump, I'd be less interested in the ICs. I can be quite lazy at times so if someone else has already done what I want, why re-invent the wheel?

Rainbows are only the very tip of the iceberg.. watch this space

Cake or Death?

Posted: 12th Apr 2005
Two cool items today...

Firrst, I think this might really be the holy grail for Luxeon driver chips:

https://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1042,C1094,D4570

Second, another way-the-heck-cool LED setup:

https://web.mit.edu/storborg/ddf/

-p.

Posted: 12th Apr 2005
Holy !! Those are some absolute gems you've found there! Might have to order some samples and have a play. That USB dancefloor is pretty cool. I can't help feeling you could adapt the idea to make a game of tetris that fills a wall

Cake or Death?

Posted: 12th Apr 2005
damn im overjoyed by that dance floor, simply amazing im sure a spinning have a nice day smiley would be sweet lol

You've got the wings of a fallen angel
You offer peace if they praise your name
You live your life taking everything you can get
Look down, time to fly!

Posted: 12th Apr 2005
Due to being a bit of an insomniac tonight, I've made a bit of a leap forward with programming some patterns. So after much fiddling of assembly, I give you 'The Stutter Fade':




Non-Https Image Link

Non-Https Image Link



Non-Https Image Link




The code that drives that could switch it to any colour imaginable. I've also written some stuff to do a generic strobe, and some stuff to set colours simply.



I just need to get my head around tables and work out some sort of pseudo-random code to pick new colours. I quite fancy trying to make some sort of fire effect too because another idea struck me yesterday. What if you turned these things round through 90°? You attach them to your finger loops with chain (or whatever) and the cones become trails. If you had a flickering orange/yellow effect, it ought to look quite a lot like fire... in fact you could have any colour! Rainbow fire anyone?
EDITED_BY: *HyperLight (1113366801)

Cake or Death?

Posted: 13th Apr 2005
Hyperlight all I can say is wow they are amazing you could give aerotech a run for their money one day if you keep it up!

Most beautiful trails I've ever seen!

*Thats one of my favourite Nurseries over there,*

Roman, Trippie Hippie,On the way back from Play Festival

Posted: 13th Apr 2005
Thanks house of mill. I must admit I had hoped these things would work well.. but had no idea they would look this good!



I have some more cunning plans in the pipeline. One of which is in the form of accelerometers. By sensing the acceleration on the Poi, it should be possible to work out where the top and bottom of the spin is. Also, faster spinning will kick out more G's. I had an idea that if you spin the things really fast (read hyperloops) it could switch into a different pattern like a really fast / bright strobing white for example... lots of ideas to be played with
EDITED_BY: *HyperLight (1113405600)

Cake or Death?

Posted: 13th Apr 2005
i love how they light up the darkest of places lol



they look like your spinning neon tubing, those are the wickedest things ive ever seen, you should write a whole how to make your own thing, that would be awesome!



you get 10 thumbs up for those! Really cool!
EDITED_BY: Spacecow00x (1113435876)

You've got the wings of a fallen angel
You offer peace if they praise your name
You live your life taking everything you can get
Look down, time to fly!

Posted: 14th Apr 2005
Cheers That's a lot of thumbs for one cow!



I might write a guide eventually, although I've been half-considering selling them.

Cake or Death?

Posted: 14th Apr 2005
I have no idea how to do circuits or basic programs or any of that thats why im in love with them, a guide would be awesome!
never thought to ask, how are they for durability?

You've got the wings of a fallen angel
You offer peace if they praise your name
You live your life taking everything you can get
Look down, time to fly!

Posted: 15th Apr 2005
Right now, they're not very durable at all - just a load of batteries and a board stuck in a modified hamster water bottle! The finished versions will be cast in solid resin and should be relatively indestructable!

Cake or Death?

Posted: 15th Apr 2005
sounds good !

You've got the wings of a fallen angel
You offer peace if they praise your name
You live your life taking everything you can get
Look down, time to fly!

Posted: 15th Apr 2005
i want one!

Posted: 21st Apr 2005
A little package arrived for me while I was away with work on a course:


Non-Https Image Link


4 Li-Ion batteries with solder tags which fit quite neatly into some of the polycarbonate tubing I've got:


Non-Https Image Link


The one on the right only leaves ~1mm gap which is a little tighter than I'd like to provide some padding for the unit. The bigger poly tube is also much tougher and probably a better a better bet as a result.

Cake or Death?

Posted: 22nd Apr 2005
Hyperlight - bit off subject here..but where do you buy your poly tubing from? I need some! thanks..

Tomorrows World isnt on anymore...Does that mean its tomorrow now?

Posted: 22nd Apr 2005
Hyperlight Wow, well done with the fade effect.

Looks like your making good progress.
Give me a shout if you're stuck for a way of making the packaging for them strong enough.
I can help...
thats my job professionally
Good luck

Posted: 24th Apr 2005
Melemel: I got it from a company called Wake Plastics. They mostly make tubing for lighting applications, but they do small quantities for reasonable prices too.

I reckon the polycarb will o for the mark 2 prototype, but I'd be interested to hear what you'd suggest for mark 3? I was thinking of setting things in some sort of resin....

Cake or Death?

Posted: 24th Apr 2005
hey *hyperligh,
do u have a schematic, or did u get a chaser sort of thing,

nice work btw

cheers, pete

"you know there are no trophys for doing silly things in real life yeah pete?" said ant "you wont get a 'listened to ride of the valkyries all the way to vietnam' trophy"

*proud owner of the very cute fire_spinning_angel, birgit and neon shaolin*

Posted: 25th Apr 2005
I could knock up a schematic, the actual circuit is relatively simple. It's programming the PIC that's the difficult bit. I'm probably going to change the way the circuit works soon anyway!



[edit]After an email from Konsti, asking if I was planning on selling these things, I've been thinking a bit about getting some testing done. Would anyone else be interested in testing some of these things? I need to get them a little further down the development road before I'd be happy selling some prototypes, but I just thought I'd guage the level of interest.



Here's a quick summary of what they can/will do...



At the moment I use 4xAA batteries, but I'm planning to start using a single Lithium Ion battery instead. Would you rather have a smaller package size (using the single Li-Ion battery), or be able to use standard 4xAA NiMH batteries? I think the thing will eventually come with a charger either way.



I'm planning to add an accelerometer so that patterns can be syncronised to where the poi are in the spin. Do you think adding a microphone to sync to music would be worth-while as well? I'm not sure how difficult it'd be, but I thought some people might like it.



I'm intending on having a way to program new light-sequences into the poi via a USB port on a PC. Does that sound like a good idea or would you rather enter programs by a sequence of taps, or button presses (along the lines of aerotech's solution)? I personally like the idea of using the PC because sharing sequences would be easier. I was going to offer a small portion of my website for that purpose.



One other thing I've been considering trying it using infra-red links to re-program the poi. I like the idea that if you knew a few people with these units, and you were out spinning, you could 'teach' your friends' poi the same tricks by sending them the sequences via infra-red.



Are there any other ideas that you'd want on a set if you had some?



Comments, questions, suggestions all very welcome
EDITED_BY: *HyperLight (1114434185)

Cake or Death?

Posted: 26th Apr 2005
editing sequences on ur pc? usb hookup? included charger?
SYNCRONISED TO MUSIC!!!!!!!!

somebody get me a towel i think i just wet my pants.

hmmmm somehow i would tend to the 4 aa battery solution to make them work at festivals and when you forget ur charger or have no place to charge.

im all in favour of pc linking options, but they should be usable without it too (maybe a already programmed set of patterns)

music sync- that would be absolutely amazing, but it shouldnt eat up battery. as long as i can turn it off...

wow, let me know the second u have a prototype ready to be send off

"is optimism in austria just a lack of information?"
-Alfred Dorfer

Posted: 26th Apr 2005
*hyperlight- I've been folowing your progress weith these for a whoile not and I must say I'm really impressed- I'm no tehie but the stuff you've achieved is nothing short of spectacular

I'm Going to be in Herefordshire over some of the summer (thats were I'm at when not at University) and seeing you're in Malvern I wonderted if you wanted to meet up, spin, test your crazy luxeons etc? Could be fun

Posted: 26th Apr 2005
*here u go Konsti have one of mine*

I want some 2!!! how much do u think your price will be on these? or is it to early to tell? xxx

tHeReS gOoD aNd EvIl iN EaCh InDiViDuAl fIrE, iDeNtIfIeS nEeDs AnD fEeDs OuR dEsIrEs.

Posted: 26th Apr 2005
@Konsti: Nice to know someone else is as excited about these things as I am Your AA battery reasoning was why the current version uses AAs. They'd definitely come with a pre-programmed set of sequences to choose from. Some of the ones I've already come up with + more.

@Chutney: Ta very much I'm definitely up for a meet - there's not enough spinners round these parts if you ask me!

@Vixen: The price depends on an aweful lot of things. Too soon to tell I'm afraid, although costs are on my mind so if I find cheaper ways of doing things, I'll be doing them that way. That's one of the reason i fancy these li-ion batteries. the cost/weight ratio are in their favour...

Cake or Death?