Light up LED earings, created for a Princess Peach cosplay. Printed in transparent PLA.
You'll also need a 5mm LED, a CR2032 battery and an earwire (the hook bit!) for each earring you want to make, plus a little superglue.
I made two pairs of these, one used plain blue LEDs, and the other used some rainbow LEDs from Pimoroni (https://shop.pimoroni.com/products/5mm-rainbow-led-pack-of-10)
You can see a video of the rainbow LEDs in action here: https://www.youtube.com/watch?v=Shw1exjkoVA
There are two holes at the bottom of the battery holder; just thread the electrodes though, one each, so they run down the inside of the holder. Twist one electrode over the front, and the back to hold it in place, leaving space for the battery in the middle, and glue the top and bottom halves together.
The battery can be slotted in between the electrodes when needed and, removed when you want to switch them off. The cover should click into place, and can be popped out with a bit of pressure or with a small flat-bladed screwdriver.
I had some luck with bridging over the top of the battery holder, but in the end I had better results by printing supports (which can be extracted with a pair of needle nose pliers). Other than for the battery holder, supports shouldn't be needed.