Safety Pin Crocodile Clips for ETextiles

For this project I wanted to make a variation of crocodile clips suitable for eTextiles. Using regular crocodile clips damages fabric and requires you to pinch materials and deform or damage fabrics and garments.

Safety pins are used all the time in garment making and alterations, so I decided to make safety pin crocodile clips which can be used over and over when testing eTextile circuits. This will allow me to quickly reroute circuits for prototyping.

more pictures: https://www.flickr.com/photos/rachelfreirestudio/...

this Instructable is part of the project Second Skin, a rapid prototyping suit for eTextile circuits on the body:
about the project http://www.rachelfreire.com/second-skin-login/
work-in-progress images https://www.flickr.com/photos/rachelfreirestudio/a...

Materials:
- insulated multi-strand wire (26 gauge)
- safety pins in different sizes
- clear and opaque shrinktube in various sizes
- solder
-kapton tape (optional)

Tools:
- soldering iron
- wire cutter/stripper
- scalpel
- scissors

I decided to make a variety of test pieces in different lengths and using different materials.

I prepared samples in three lengths: 50cm, 30cm, 20cm.

Cut the wires to size and choose the safety pins to go with them. In some cases I chose pins of different sizes for two ends of the same clip.

For my first test I decided to use two layers of shrinktube: One to protect the joint where I will solder the wire, and a second to wrap around the pin, in a similar way to a traditional crocodile clip. I chose clear shrinktube for this second layer so I could see the pin and joint inside.

1. cut the shrinktube: I cut about 8mm red shrinktube to protect the solder joint*, and 3cm clear shrinktube to wrap around the safety pin. I was using what scraps of material were available at the time. You could also use larger pieces.

2. strip about 1cm off the end of each wire, enough to wrap around the pin and twist to secure

3. thread the shrinktube on the wire before you solder. Arrange the larger clear pieces furthest from the pins, and the smaller red pieces closer. This is especially important it both kinds of shrinktube are the same size as they wont easily slide over each other. You want to shrink the red pieces on to the joints first.

4. wrap the exposed ends of the wire around the pins and carefully solder the joints, leaving as little wire exposed as possible

5. shrink the red tube protecting the joint until it is tight (You might want to use kapton tape to protect the wires). Then shrink the clear outer tube. this does not have to be shrunk fully, depending on the size. The tubing I used was already quite small and thin so quickly shrank to fit

*this would also be good with glue lined shrink tube

I tried next with a single layer of shrinktube. After making the first piece I realised the shrinktube casing didn't really move the way I has wanted, so maybe having the second protective layer was unnecessary.

I made two pieces, one with clear shrinktube, which is quire soft, and another with opaque white, which is more sturdy. I will test these to see if they last longer than the double layer clip.

Both were made with pieces of tubing to match the varying sizes of the pins, and leaving different amounts of pin head exposed.

I decided that it was better to use two layers of shrinktube as the second layer does get disrupted by the movement of the pin. Using clear shrinktube is better as you can see if the soldering points are strained or broken.

I also like everything to be see-thru! These are definitely my favourite, aestheticelly. I like to be able to see the whole pin.

For the first layer of shrinktube, I used longer pieces of tubing than the red ones in my first test.

These were made with different sizes of safety pins of each end.

Conclusion:
The safety pins work really well! In the first picture they can be seen routing a circuit through tubes in an eTextile bodysuit and connecting to stretch connectors and bonded conductive fabric. This was done at a show when a hacked battery failed.. the pins allowed me to quickly reroute a circuit for a demo. They run through the panel you see in the picture, and also all the way around the suit to the back of the hip to light up lillypad LEDs.

The best thing about them is that you can pin through a conductive fabric trace at any point on a circuit (in this case the trace on the chest was insulated!) and make an immediate stable connection. It worked beautifully!

This was a first test of an idea, and didn't quite turn out as well as I had hoped. I was using leftover materials which limited the process a little. Next time I will use more specific shrinktube, based on this experiment.

Improvements:
The one failure here was that the shrinktube does not slip over the pins as it would with a regular crocodile clip. because of the nature of the pin head it leaves a lot of metal exposed and is therefore not so good for small areas or close, exposed traces.
In the next version I will take this into account, looking for a practical way to expose as little metal as possible, while maintaining the mechanism of the pin.

In the meantime, these are still really useful and quite simple to make.

Related Instructables:

https://www.instructables.com/id/Stretch-Circuit/ technique for the insulated stretch circuit seen in the above image

https://www.instructables.com/id/ETextile-Glove-Wi... more hacking eTextile circuits with pins (see end of instructable)