Sewing LED Matrices

[mrex]

Hi All,

I have a mad plan, and it involves scrolling text through an 8 x 64 LED matrix. But I want the matrix to be embedded in frabric, using the conductive thread I just bought. I want to sew this matrix into clothing, hats, whatever. I want these matrices to be light, beautiful and a joy to see in action.

I think sewing/building my own matrices with SMDs and ferrules are the way to go, but I'm not sure.

Can I build/wire/sew something like this, and then drive it from Flora and some MAX7219CNG chips?

I have been surfing adafruit.com's videos and I seem to remember some part of one video where Becky Stern (?) is soldering small iron rings (ferrules?) onto the ends of SMD LEDs, as if she is going to sew them up into a matrix. It seems like the perfect idea to me.

I would want this matrix to be so light. so soft that I could make a sash, a choker, an arm band or shirt sleeve ruffle out of it. I don't mind the tedium of the work involved in wiring it all up, but I think I better ask before I get started.

Any clues? I have a million questions -- where do I get small ferrules to solder to SMD LEDs? A bead/craft store? What kind of fabric should I use, how thick should it be? How can I waterproof it? What about heat (I certainly don't want to burn anyone's skin!)?

I bought some conductive thread, but I haven't played with it yet. I also bought 2 8x8 LED matrices and two MAX7219CNG chips, and I'm actively breadboarding and learning how to control them through Arduino. And I have a Flora...

Note that 8 x 64 = 512. Should I think of a way to bake the ferrules onto the SMD LEDs using my oven? Can this even be done using a sheet of aluminum foil and SMD soldering paste? I will solder 512 individual LEDs if I have to, but I think I should think it out first. Its a bit of a manufacturing problem. And then there's the wiring...

Any clues appreciated, please chime in!
-- Clueless Mrex

P.S. Sorry if I've missed any other posts on this, please point them out...

[janekm]

Wiring up individual LEDs, in a 8x64, using conductive thread, sounds practically impossible to me. You'd have wires crossing next to each LED, and then you'd have to somehow bundle up the 72 wires and bring them to your driver board. Definitely not a beginner-friendly project!
I'd look at either using the Flora smart pixels or the Neopixel strips; both of those can be hooked up serially making the wiring much more practical.

As regards your question of hooking up the ferrules to the LEDs, yes those ferrules come from bead stores; if you wanted to mass-assemble them you might need some kind of jig to hold the ferrules next to the LEDs in the oven. Though you could try just sticking the ferrules onto the LEDs using solder paste and sticking it in the oven... If you're lucky, the surface tension will keep them in the right orientation, if you're unlucky it'll turn them around and you'd need a jig. Worth a try anyway. It's advisable not to use the oven you use for cooking for soldering, as the fumes from the solder paste are not that healthy.

[mrex]

Thanks for the reply Janekm, you've got me thinking...

Wiring up individual LEDs, in a 8x64, using conductive thread, sounds practically impossible to me.

Challenge accepted! First off, I'll use 3 layers of fabric. The LEDs sit on the top layer. The second layer contains horizontal lines for rows, the third layer contains vertical lines for columns. First I sew loops hooking the anode ferrules to the horizontal lines, using the top and middle layers. Then I add the bottom layer, and sew loops hooking the cathode ferrules to the bottom layer. I position the LEDs at a 45 degree angle and space the lines accordingly.

and then you'd have to somehow bundle up the 72 wires and bring them to your driver board

Now this one is tougher. Considering I'm trying to emulate the 8x8 LED modules like the BL-M12A881UR-11 I probably have more than 72 wires. I believe I have 16 x 8 = 128 wires, which would be an ungodly mess of individual lines. However, if I continue to think of 8x8 modules, that's only 16 lines per, maybe I could run them to perf board at the bottom edge of each segment, and then use 16 conductor ribbon cables to get to the driver board. I end up with 16 ribbons.

I have to do some more thinking about this one tho. Attaching the thread to wire wrapping wire might also work, if I again created bundles of 16 and color coded the ends.

Definitely not a beginner-friendly project!

Go big or go home. Seriously, this is *not* a simple idea, and I expect to have to work out many problems in stages. Before I get to 8x64, I think I have to get 8x8 working. And before I get an 8x8 working, I'd better make some easier fabric-based projects. But that's part of the fun isn't it?

I'd look at either using the Flora smart pixels or the Neopixel strips

I did. They both look too big. But I'll look at them again...

And finally, thanks for the pointers about using a jig for soldering the ferrules, and *not* using my oven. If I can come up with a "10 at a time" jig that lets me solder them in say, 5 minutes (including setup time), that would be 512 / 10 * 5 / 60 = 4.27 hours of work.

-- Contemplative Mrex

[janekm]

You might not need all 3 layers if you have a cunning arrangement of stitches.

Actually your thought of building 8x8 modules is smart; I would put a local driver chip on each of those modules (or ideally even smaller sub-modules, maybe 4x4) so that you can send the data serially to all the modules. The local drivers could be simple shift registers or a micro controller for some more local smarts.

I believe a practical solution for soft fabric LED matrices is something a lot of people are looking for so it's certainly worthwhile!

With a bit of practice and a jig you could probably do better than 5m /10.

[fran52]

Google "conductive thread" or try

Sparkfun DEV-08544

If this is not strong enough, try wirewrap tie wire. Seam tape and binding tape can hide
some of the circuits. Making a "tube" of binding may allow removal of the circuit for laundering,
pouches for pcb / batteries / controls. Even ring magnets to attach different displays/badges.

More ridgid units can be mounted in a belt pouch with a plug interconnect running up the side seam
of your shirt or jacket to connect a power hungry shoulder based display.

[mrex]

Thanks for the replies Guys,

@fran52, I already have two bobbins of conductive thread from Adafruit (http://www.adafruit.com/products/640 and http://www.adafruit.com/products/641). I'm thinking of wrapping/sealing the whole thing between two sheets of plastic, and making it both removable and waterproof. You never know when you're going to get caught in a good Thunderstorm...

@janekm, I'm afraid "a cunning arrangement of stitches" may be beyond me, I'll vote for the KISS method and stick with as many layers as I need to keep things from shorting out.

At the same time, I also had the idea of putting a driver chip behind each 8x8 matrix -- that way I reduce the number of actual lines to 5 -- Vin, GND, Din, LOAD and Clock. I'd have two sets of lines, one for incoming lines from the main microcontroller, and one to connect to the next 8x8 module. This is the same idea as the Neo Pixel. Thanks for that one!

Also, in terms of current, I'm beginning to think 8x64 is a bit much, and 8x32 might have all the "readability" I need. I've just spent some time breadboarding a single 8x8 matrix, and that's quite usable by itself for scrolling simple text right to left...

As usual, any other thoughts appreciated, and all clues welcome.

Signed,
Looking For A Notions Store Near Me

P.S. I live smack in the middle of Manhattan's Upper West Side. Anyone have a clue where I should go to get an embroidery hoop?