Other power options and microcontrollers are available, but the DigiSpark is largely black, was best use of space for my design and have used it before. (I have a couple of trinkets kicking about but never used them).
Power-wise, i wanted to avoid LiPo, and went for 2xCR2032, but they just wouldnt have enough uumph to do the job when the brightness went up.
2
Step 2
Measure, plan, measure, and measure again.
I tried lots of spacing options but eventually went for 25mm gaps between the slots for the leds, this allowed me enough space for batteries, micro and switch at the end.
3
Step 3
Cut the slots for the leds.
Make sure you use a fresh blade in your scalpel/craft knife, leather is tough stuff and you want clean cuts.
Don't cut too close to the edge of the collar otherwise you will compromise its integrity.