Cut a small piece of fabric about 8"x8". Place your cabochon in the middle and trace around it on the wrong side of the fabric. Cut a hole for the cabochon that's a little smaller than your mark so the cabochon won't fall through.
Fold your fabric in half around your electronic eye and mark where it meets itself. Sew the raw edges together with the right sides facing inwards.
Flatten the fabric so the hole is on top and the seam is at the center back. Stitch a curved edge about 1 inch below the hole. Make sure the electronics fit nicely inside.
Place your cabochon into the hole, face down (so you're looking at the flat side). Run a bead of glue all around the edges to hold it securely in place.
Turn your case right side out and gently slide the electronics inside with the switch and photo cell coming out the open top. With a utility knife, make a small slit above the USB port. Make another hole for the photo cell sensor to poke through.
Sew up the top of the case with a needle and thread, leaving the on/off switch accessible. I finished by coloring my on/off switch with a paint pen so it blends in better with my case.
Finish up by attaching a necklace cord, or leave it as-is and keep it safe inside a potion jar.
Remember that the OLED screen is really delicate, so do NOT try and squeeze it into a jar that's a tight fit -- you can break the screen if you squeeze it too hard.
Charge it up by plugging in a USB cable -- the indicator light on the charger will turn green when it's fully charged.