Author Topic: coolest wearable electronics project ever  (Read 4510 times)

albercook

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coolest wearable electronics project ever
« on: October 31, 2013, 12:20:23 pm »
I teach middle school science and the Chameleon Scarf from Adafruit is very appealing.  I have no trouble getting lots of interest in building one. The problem is the cost.
The Flora $25
The color sensor $12.50
12 NeoPixels $24
SS thread $7
Lipo battery $6
Battery charger $6
Total $80.50

This just takes the project out of the range of students.
I can use the DigiSpark which will save me $16. There is a color sensor on DealExtreme http://dx.com/p/tcs3200d-arduino-led-rgb-color-sensor-module-138020 that saves me another few dollars. The big remaining cost is the NeoPixels. Since each LED will be the same color I was thinking that I don't need the address-ability feature. So I could use simple tricolor LEDs. I coudl just PWM the power to the three colors. Than all the current would have to be delivered on the PWM line I would need three transistors. 

The light output from the NeoPixel(ws2812) is approx. Red 600 mcd, Greeen 1200 mcd, and Blue 300 mcd. While the tricolor LED on DigiStump is red 3500 LM, Green 7000LM, Blue 4500LM. Both seem to be about 150 degree viewing angle. I know that mcd and LM are difficult to compare. Does anyone have both? Are we looking at a factor of 2 or 200 difference? Both draw 20mA/color.

I think I could fit mosfets and resistors on a protoshield.

Any thoughts would be much appreciated.

dougal

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Re: coolest wearable electronics project ever
« Reply #1 on: November 01, 2013, 05:48:46 am »
Another option would be to buy an LED strip. The 30 pixel/meter variety is only $16 from Adafruit. You can slice it up into three 10-pixel chunks (or slice down to individual pixels and rewire them all). In any case, it cuts your LED cost about in half. Or you can get the non-addressable ones at $25 for a 60-light strip, which gets you down to $5 for 12 lights.

Also, instead of using a lipo and charger, how about AA batteries? 3 alkalines @ 1.5V each gets you 4.5V. Or 4 rechargables @ 1.25V each gets you 5V. Since AA battery rechargers are pretty standard, you might not have to feel obligated to include the charger cost.

I'm guessing this could bring things down to the $40 range (+/-)? Still not "cheap" by many people's standards, but definitely way more reasonable than $80.

albercook

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Re: coolest wearable electronics project ever
« Reply #2 on: November 01, 2013, 06:45:33 am »
Thanks those are great ideas.

If I breakdown the longer pixel strips any thoughts on how to connect them to the SS thread? I could drop the SS thread entirely and use stranded wire.

I really like staying with the addressable option. It makes for so many programming options.
The AAA battery is a slam dunk. Do know why I didn't think of that. They even talk about it in the tutorial.

Bluebie

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Re: coolest wearable electronics project ever
« Reply #3 on: November 02, 2013, 04:32:26 pm »
Since it sounds like you'll be making this a few times, I recommend going on aliexpress.com and searching for 'ws2812 60' and pick yourself up a roll of about 5 meters of 60 led per meter strip, without plastic cover - just the plain uncovered strip stuff. It's easy to cut in to individual lights with regular scissors and I've just tested it now and found it is also easy to sew through. They have little via holes on the solder pads of the flexible PCB material, and the flexible PCB is soft enough that the holes expand very easily with a small needleneedle. I think you wouldn't have trouble using them with conductive thread. Make sure you get some quick drying clear enamel (nail polish is good) to cover over the connections too so the thread isn't moving around lots and making the lights glitch out. Adafruit have some great tutorials on this stuff. Another neat thing about this stuff is the non-waterproof lights often have an adhesive back, so you can peel off the tape and stick them down to your fabric, then sew them in to place with the adhesive keeping everything lined up well. It is also easy to peel the adhesive off if you don't want it.

AliExpress vendors usually send their products via fedex or dhl, so you'll get it in just a few days instead of the two months or so that dealextreme usually takes. DealExtreme gets their products from the same factories who sell direct on aliexpress, and aliexpress has a much bigger range, but you usually have to order larger quantities. 5 meters of 60 led per meter gives you 300 lights, for about $50 in total. It works out being about 20ยข per light - so much better value than all those flora/lillypad lights on hard PCBs which tend to work out at closer to $2 each. If you like playing with light, I promise you will like having a roll of these lights on hand. I haven't done PWM on a microprocessor in a long time! It's great to have LEDs which don't need any resistors, and I was actually paying more for my RGB leds before. ws2812 are so much better!

Many adafruit products which aren't their own custom designed in house PCBs just come from alibaba/aliexpress anyway, and cutting out that reseller will save you a lot of money if you can meet the minimum quantities required by aliexpress. If you're teaching a large enough class you may even be able to order components from alibaba, where factories will be happy to make custom designs for you in many instances.