Repurpose a dollar-store bicycle safety flasher to embed in the scarf. Simulates the light changing pattern and does other fancy sequences. No arduino needed.
The technology is borrowed from the earlier Lithium Rain Radiant Beacon of Righteousness (Blinking I-hoodie).
Step 1: Stuff to make it
You can use any soft fabric that doesn't stretch too much as long as it is comfortable to touch when you wear it.
You need something that equates to a strip of fabric about 12" wide by 60". The fabric is doubled over lengthwise for a finished scarf width of about 6 inches. It can be shorter or longer as you like.
Use remnants to piece together the scarf for a more varied look.
The electronics in this scarf is based on a dollar-store bicycle safety flasher. It is a self contained unit to house the batteries, has a switch to cycle the light patterns and contains 5 red LEDs.
You will need to mod it to add yellow and green LEDs. Some flashers may have all white LEDs which you can adjust by the filter material but you will still need to mod the flasher unit to extend the LED from the circuit board. Soldering skills are required.
You will need some clear plastic adhesive shelf liner paper.
You will need a plastic shopping bag in red, yellow, and green to use as color filter material. Come to think of it, none of them are really "green".
You can hand sew this but a sewing machine is much more efficient. I also use a serger which is great for simple projects like this.