Wearable computing, e-textiles, soft circuits or whatever you want to call it, is a growing field of applying technology to garments or accessories like bags, shoes or backpacks. It is a fun and creative challenge which goes beyond just adding LED lights to fabric. For a primer, you must check out the work of Lynne Bruning.
Of course, to make things light up really cool, you need some kind of microprocessor. I have always used a bicycle safety LED flasher from my dollar store as the core unit of several ibles because It was an inexpensive self contained unit that had everything I needed, battery case, on/off/pattern switch, 5 LEDs and could cycle through different lighting sequences. You can make everything from light up hoodies, signal gloves, stoplight scarfs and logo scarfs.But then you feel the restraints imposed by the limits of the bicycle flasher. I finally got an arduino a few months back and started to experiment with it. Using it with an accelerometer allowed me to create a set of necomimi arduino cat ears.
Well, they are all examples of wearables but another part of the puzzle was missing. I had always used wire, regular insulated wire, as the circuit path for the circuits. Conductive thread is what makes it a true wearable. I finally have a few bobbins to experiment with. Conductive thread is fine metal fibers twisted into a soft thread or yarn. It is truly flexible but needs to be insulated when crossing wires.
But then you will find, jumping into the world of arduino is not really cheap. Costs add up with additional components. I only have an Arduino Uno. Now what to do when all the wearables are done with a Lilypad. No one can get their hands on a Adafruit's FLORA yet.
Here is my solution to using your ordinary Arduino as the microprocessor unit on your wearables. An easy mounting "shield" and a bus adapter to get the pinouts from the headers on your Arduino to your fabric...sort of a digital to real-world analog interface. I think it is hard to prototype when all of your input wires to the arduino are hard sewn to the "header". When you troubleshoot or prototype, you have wires that you need to disconnect or rearrange. This wearable shield also takes your prototyping directly to the finished product. The core arduino can be removed easily for use with other projects. Also, remove the arduino if you need to wash the garment. Hmmm, dry clean copper wires only?
Step 1: Support Your Local Electronics Greengrocer...
We don't need anything too exotic for this project.
You will need:
Tyvek envelopes - this is that miracle indestructible rip-proof matted-fiber polyester film shipping envelope stuff - reuse if you have any or acquire at the snail mail office. Ones marked Express do not work any faster than the Priority ones.
ordinary metal paper single hole puncher
22 AWG gauge solid hookupwire
generic sewing machine - nice to have a zigzag stitch or do everything by hand
generic soldering stuff and electronics working tools like pliers, wire cutters, wire stripper
and the secret ingredient - solder wick (desoldering braid)
Optional to dress up the connections:
sugru or plumber's epoxy putty
fray-check or seam sealer
CAUTION: Learn how to sew and solder safely.
Two things Three things that mix.
Step 2: Dice and Splice...
Cut open your tyvek envelope to get a single flat sheet of material.
Lay out your arduino on a layer of the tyvek envelope.
Cut a piece about an inch larger all around the arduino.
Use a pencil or pen, whatever can fit in the mounting holes to mark the positions of the mounting holes.
Fold the excess under forming a piece that is approximately the size of the arduino.
You should have enough folded under to double the layer where the mounting holes are.
Take your hole punch and punch out at the mounting holes going through both layers.
Punch an additional hole next to each the mounting holes. They should be at least a hole diameter between them. A tie-wrap will be threaded in the hole. If you place the holes too close together, the tyvek can actually rip apart if you pull hard enough. Using a regular paper hole punch might leave dangling chads in Tyvek. Clip them off with scissors.
Orient your mounting shield on your garment. Sew around the edge of the mounting shield. If you really want to go nuts, also bar tack around the mounting holes for a finished buttonhole look or sew an X through the middle to really secure to the garment.
Place arduino on the mounting shield. Pass the tie-wraps through the mounting holes and the mounting shield.
Secure and clip off excess tie-wrap ends.
Your arduino is now securely mounted to your garment for use. It can be easily be removed and remounted as many times as needed. I also thought about using those motherboard plastic mounting push-top rivets but then you still need to mount a set of matching motherboard standoffs to a substrate to sew on. Anyone can do this.
Step 3: How to Hookup...
Now that we have the arduino secured to the garment, how do we get the wires to the components on the garment?
Well, we need to interface the hardware to the soft circuit part. All of the wires that input into the header on the arduino need to be transitioned to the conductive thread.
Lightbulb! No, solder wick!
Solder wick (desoldering braid) is a braided product of thin copper wires. I guess you could classify it as a really really coarse conductive thread. It's only use seems to be it was designed for desoldering operations to soak up molten solder to remove it from circuits. We want to do the opposite.
If we mate a piece of solder wick to the end of an input lead, the braid can be sewn through with conductive thread to make a solid physical connection.
Tin the end of the solder wick to keep it from fraying.
Depending on how long you want your sewing connector, 1/4 to 1/2 inch is good, stab in one end of your input wire. You can bend it around to dig into the braid.
Solder the connection being sure to get the solder to flow across the end to stop the frayed end.
Clip off the solder wick spool.
Straighten out the assembly.
You can run it through a sewing machine by doing a wide zigzag stitch over it. Yeah, my sewing machine needle nicked the braid a few times but it punched through. Use a heavy duty needle if you are worried. I would have oversewn the wire too if I had a bigger presser foot on the sewing machine. Wait...doesn't everyone use their machines to sew stuff other than fabric?
I did notice some corrosion or patina in some of the core of my solder wick. I can't tell if it is old wick or was just stored in a humid place. It is removed easily with a pencil eraser or light sanding/scratching with a utility knife. It might be rosin too so just heat it off with a soldering iron. Once you verify a good connection with the sewn conductive thread, you can put on a dab of hot glue/fabric paint/seam sealer/fray check to possibly seal it from any further corrosion.
Once you have the transitions sewn down, bundle all the leads and secure in a wire harness to the tie-wrap loops that are on the mounting shield. Envision where all your wires are going to be and you can plan to punch additional holes in the mounting shield to accomodate more anchor points for the wire harness that might run through the middle side of the arduino.
When all of the input leads are in the header, pack a glob of sugru, epoxy plumber's putty, or maybe ooglo around the wires to form a solid header. Put some masking tape around the actual header to keep it clean. When cured, it will keep all or your wires in correct plug in order if you do remove the arduino. Just plug and play.
Make a mounting shield for your battery pack and other accessories.
Step 4: Sew What?
I've got the regular ones and some SMD ones to try out. I'll figure out the SMD ones later.
The usual method is to wind up the leads to make a loop that you can sew with conductive thread. I want something I can zip through my sewing machine that is using conductive thread.
How about attaching some conductive solder wick to the ends of the LED leads?
Take your LED and bend the leads out slightly.
Punch both leads through the solder wick. You can use a needle or your seam ripper to start the hole in the solder wick. Or pull it apart slightly to open up the braid. But then you have to reform it to close back up the wide gap.
Solder the leads to the wick.
Tin the free end of the solder wick.
Tin the part where you want to terminate the end of the solder wick.
Clip off and clip between the leads to separate the two leads.
You can put a dollop of hot glue, micro heat shrink. dab of liquid electric tape or epoxy to make sure the gap never closes up and creates a possible short in your circuit.
You may have to experiment with how long of a braided lead you need to pass under the presser foot of your sewing machine. The LED does get caught up and will not pass under the sewing machine presser foot.
Step 5: Get Going...
So there you have it.
A way to attach and remove your arduino to garments. A way to implement machine sewable components to interface with your arduino.
Go and make it wearable.