Electronics > Beginners

Current project: Microcontrolled LEDs to go into hair extensions. Serious topic!

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thedigitalprincess:
Ok, so in my spare time, I enjoy making and then selling (usually a custom work) funky weird hair extensions made from tubular crin (craft ribbon) called Cyberlox. Fun things, but they're even more awesome if they light up.
This is what they look like, there are two "falls"> http://sphotos.ak.fbcdn.net/hphotos-ak-ash1/hs549.ash1/32059_392809982922_50188822922_4247985_2001523_n.jpg
Some colours are highly UV reactive and glow like crazy things. This is my friend Gem, we were at a goth club > http://c1.ac-images.myspacecdn.com/images02/82/l_2a26368b40f243d2b24f6c27d4ba651c.jpg
Some goth clubs don't have blacklights and we like glowy things, so here we go...

So story starts here...
A programmer friend of mine had purchased some UV LEDs (but this is going to work with all colours really, just need voltage adjustments). So basically he has been trying to create strings of LEDs that are controlled by an AVR micro which is programmed via his Arduino. He has had problems burning onto the PICs, which would be cheaper to use in this case, so we're looking at using AVRs. If we used sequential logic, we would have at least 3 chips going.
What we want to do is create strings of these arranged in the charlieplex configuration so it becomes a light chaser when programmed. The programming allows the LEDs be dimmed. Up to 30 LEDs can be run from one chip, so 5 strands of 6 LEDs in each "fall".

Problem is, we need to keep under budget, so we can make somewhat of a profit (or at least break even) when these are sold on. We want to be able to use the cheapest and lightest form of power available. This has to include batteries and a holder to put the batteries in so the person who purchases it can change the batteries as required. We can get away with using AAA batteries, but only if we use 3V on these LEDs, which isn't so bright. The batteries can get heavy, so we're thinking coin cells. We want these LEDs to operate at 5V. Weight is the key issue, we can't have them too heavy because it's not fair on one's scalp to pull the hair so hard. Cyberlox are very light to wear, so we want to keep it as light as possible.

The budget is $20AUD for the project, because the hair extension customers won't want to pay an extra $50-$100AUD for this sort of thing.

Any suggestions for batteries, battery holders and Arduino advice?

And by the way, I'm only very new to Microcontrollers, we've only just started our lessons at TAFE/college, so think of me as a layman!

Cheers!
L.

PS ~ We wanted to use EL wire in these hair extension bobbies, but the inverter is too big and too heavy, so LEDs were the next option!

Mechatrommer:
i wish i could help, but there are criteria that i dont understand:
1) charlieplex configuration?
2) 5 strands of 6 LEDs in each "fall"
sorry, i'm a nerd guy that gets clumsy when dragged to a party.

all i know for now, is that:
1) your fren in the 2nd pic is gorgeous! so i guess, so do you!
2) the 1st picture is scary!
3) the leds in the hairy thing in the 2nd picture is like all over! not 5 not 6 ???

i doubt that one or two 5V cell battery will last for an hour with those bright LEDs.

Zad:
Charlieplexing is a method devised by a bloke at (I think) Maxim, for multiplexing many LEDs on not many wires. It takes advantage of 2 points.

a) An LED only illuminates when forward biased, so you can put 2 LEDs back to back and illuminate one or the other depending on the polarity of the voltage.

b) LEDs drop a specific voltage. This means that, for example, if you have a single LED in parallel with a series chain of 2 LEDs, only the single LED will light, the voltage being insufficient for the series pair to illuminate.

If you have n wires, it enables you to illuminate n*(n-1) LEDs. 2 wires = 2 LEDs, 3 wires = 6 LEDs, 4 wires = 12 LEDs and so on. The down side is that only 1 can be illuminated at once, and that each wire need to be capable of being driven high as well as low.

Here is a page from my notebook that I drew when I was tryng to find out how to create a long string of multi-colour Christmas lights. It may or may not help, as I was thinking as I went along:



Edited to add: how about using flexible PCB for each fall, rather than wires? Not cheap though, I must admit.

alm:
My $ (AUS or US) 0.02:
- I'm assuming you already know this, but you can just use an AVR micro, no need for a complete Arduino board, which would be way too large. Not sure why it would be much more expensive than PIC in this case, just pick a device that's cheap and large enough (ATmega48?), and program it in C. AVR and PIC would both work fine. If weight is an issue, you should use SMT (SOIC/SSOP/TQFP) packages, the smallest you can comfortably solder. Use in-circuit programming so you don't a socket.
- Charlieplexing to save pins sounds fine, you can do both continuous (at least for the human eye) and various patterns.
- What kind of current do the LED's draw? Can you drive it from logic pins or do you need some sort of transistor array (eg. ULN2803)?
- Since the micro is probably idle most of the time, you could design a boost converter with PWM from the micro as controller, this would allow you to get more juice from the batteries, with just a few external components (logic level MOSFET, inductor and fast diode). Example project, which even powers the AVR itself from the boost converter..
- Do you incorporate the batteries into the extensions or do you put it on the back? Seems plenty of room to hide two wires running down the neck, but you'd need to spend a few extra $$$ for housing and attachment.
- I don't think coin cells would have enough juice, but 2AAA might be OK. Just do the math with average current draw and battery capacity. If you don't use a boost converter, make sure to check the discharge curve, because you might only be able to use a fraction of the capacity before the voltage gets too low. I would stick to batteries that are easily available. If you're really pressed for power/voltage, you could consider CR123 lithium cells, these are widely available, but often expensive (unless you buy them in bulk).

thedigitalprincess:

--- Quote from: shafri on July 22, 2010, 05:12:49 pm ---i wish i could help, but there are criteria that i dont understand:
1) charlieplex configuration?
2) 5 strands of 6 LEDs in each "fall"
sorry, i'm a nerd guy that gets clumsy when dragged to a party.

all i know for now, is that:
1) your fren in the 2nd pic is gorgeous! so i guess, so do you!
2) the 1st picture is scary!
3) the leds in the hairy thing in the 2nd picture is like all over! not 5 not 6 ???

i doubt that one or two 5V cell battery will last for an hour with those bright LEDs.


--- End quote ---

What you don't understand:
1) I don't know much about it either, but it is an effective way to save pins on a chip.
2) Don't worry, I'm a nerd girl, but I'm an alternative chick too, so nerd + goth = party animal. Easiest way to explain a fall... It's a hair piece that "FALLS" over a ponytail. Anywho, I sell them in pairs, so they go on pigtails, thus will require 5 strands of 6 LEDs (we will be putting them inside the tubes) on each fall.

What you do know:
1) My friend IS gorgeous and I love her! Me? I'm a trashbag > http://sphotos.ak.fbcdn.net/hphotos-ak-snc3/hs324.snc3/28821_428028470534_590260534_5852658_2252538_n.jpg
2) I love my foam head! She's pretty!
3) That's about 3 or 4 large UV lamps shining onto them. :P We're looking for a portable glowing solution!

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