Combining electronics and textiles is fun, but making the transition from soft textiles to hard electronics is often difficult. If you have plenty of space and only need to connect a few wires, you can become creative with snap buttons or hooks and loops. However, if you need many connections in a relatively small space, there are not many options. In my quest for a simple textile connector that is easy to make, I've found this to be the easiest and most elegant solution so far.
So, let's use a simple pin header to make a simple yet fairly robust connector!
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Step 1: Sew Your Solderpads
The first step is to sew / embroider your electronic circuit using conductive yarn and terminate the wires by making tiny solder pads. Make sure you leave at least 10 cm of base material (for example cotton) at the end of your solder pads, since we'll fold it over the connector a few times.
Also, the base layer must not be too thick since we'll stick both ends of the connector through a few times. (The short end once, the long end twice.) The thicker the material, the harder it is to solder and if the material is really thick a female header will not mate any longer with the connector.
Most pin headers have 2.54 mm pitch and this turns out to be about the minimum for easy soldering with textiles (in my limited experience). Much smaller than this and you'll have an increased risk of short circuits!
Most pin headers also are about 11 mm long (with 6 mm at the long end). If you can, please use some pin headers which are slightly longer (12 or 13 mm) since these will fit slightly better with the female headers.
Make sure you use 100% cotton or some other heat resistant material as base layer, since we will be soldering directly onto it and it should not melt or burn! If unsure, test this out first on a sample of your material by holding your hot soldering iron and solder to a patch of your material.
Also: if you use a sewing machine or embroidery machine, make sure the non-conductive thread _IS_ made of a polyester based material since we actually want this to melt away during soldering.
Finally, make sure your conductive yarn is insulated with a material that can melt away with your soldering iron. For this connector we've used some yarn from Elektrisola (sorry, don't know exact type; it was a copper based 10 x 0.04 mm yarn) but I've also successfully used ordinary inductor wire in the past (for example Block CUL 200 / 0.10). Do note that the inductor wire breaks much more easily so you have to carefully adjust your machine to this wire. As long as you can melt the insulation away with your soldering iron, it will probably work.
In the picture we've used an embroidery machine and placed some embroidery paper for additional stability of the machine. Unfortunately we did not have water soluble paper, so the result is a bit thicker and less flexible than we would have liked. Also, the paper cannot be removed and does not melt away when soldering, so the solder connection is not as reliable as we would have liked.
Step 2: Place Connector
Place your connector on the solder pads and draw 2 arrows just above the plastic housing. This marks where you should punch the connector through. (Note that I've drawn the arrows a little too close and had to re-insert the connector.)
Insert the long end of the connector at the opposite side of the fabric and use the dull side of a knife and / or a female pin header to push it through the fabric. Unfortunately the pins of a pin header are not very sharp, which makes this a bit tedious.
In the 3rd picture you see the short end of the connector sticking out of the fabric on the opposite side of the side with conductive yarn.
In the 4th picture you see the long ends sticking out on the fabric on the side with the conductive yarn.
Step 3: Stick Short End Through the Fabric
Use the same procedure to stick the short end of the connector through the fabric again. Make sure that the short end of the connector aligns well with the solder pads.
Step 4: Solder!
Heat up your soldering iron! I usually set mine to about 380 degrees C to easily melt away the insulation. Note that soldering is quite a bit more challenging than soldering on normal PCBs since textile is flexible and has no solder mask. It is a bit messy and takes some practice but after a few pins you'll get the hang of it.
Note that a little below the connector I've also soldered the conductive yarn. I did this to be able to test the connections. You don't have to do this of course or you can do it in another area.
Step 5: Fold 1
Since the edge of the fabric was a little rough, we've folded about 1 cm over and pinned it with some sewing pins.
Step 6: Fold 2
Fold the textile over and measure the length of the fabric from the connector to the end (see picture)
Step 7: Fold 3
Divide the length of the previous step in 2 and fold the fabric again. Push the pins of the connector through the line of this fold. Use a female pin header and sewing pins to hold everything in place.
Step 8: Sew!
Use your sewing machine and ordinary sewing thread to sew over the length of the fold. Stop when you're close to the connector since the connector is too thick and too hard for the sewing machine. It will cause damage to your machine!
You will end up with a connector that is sewn into the folds of a double pocket. You can leave the pockets open so you still have access to the solder joints and can repair them if needed. However, for a more robust connection we recommend to add some textile glue to protect the connections.
That's it! Congratulations! You've just made a textile connector!