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Designing electrochromatic circuits

24 Dec 2015  | Dia Campbell, Diana Eng

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Have you heard of electrochromatic circuits? These utilise electricity to make something change colour. It's very experimental, so you won't see anything electrochromatic for sale in the store. Here's a tutorial to get you started making your own electrochromatic circuit. You will combine thermochromatic pigment (which changes colour when heated) with steel conductive thread (that will heat the pigment in a short circuit). When you push a felt button, your electrochromatic circuit will turn on, and a design will appear in the thermochromatic pigment.

Required materials
Craft materials:

 • Scissors
 • Felt (to create the button)
 • Thread
 • Thin Fabric to paint your electrochromatic design (quilting weight works well)
 • Fabric Paint
 • Paint BrushPaper Plate (to mix paint on)Fabric Glue

All of the parts for this are included in the Sparkfun 21st Century Fashion Kit:

 • Polymer Lithium Ion Battery—850mAh
 • SparkFun MOSFET Power Controller
 • Needle Set
 • Conductive Thread Bobbin—30ft (stainless steel)
 • Thermochromatic Pigment—Sapphire Blue (20g)

Making a soft circuit button
In this section, you will use conductive thread and felt to make your own button. When you push the felt, two pieces of conductive thread inside of the button will touch turning the circuit on.

To begin, cut a piece of felt for the top of the button and a piece for the inside. Cut a small hole in the inside piece of felt (the conductive thread will touch through this hole when the button is pushed).

Using the conductive thread, sew from In+ on the MOSFET power controller to the side of your button location. With a second piece of conductive thread, sew from In− to the bottom of your button location. For a strong secure connection, stitch through the through-holes in the board a few times, and make sure your stitches are tight. The two threads should not touch. Tip: Don't use your fancy sewing scissor to cut the conductive thread; it is steel and will dull them.

With one thread, create a long stitch in the fabric that will go under the button. Sew back over the stitch three times, then tie off the thread on the back. Cut off any loose ends.

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