Yeah, you heard me right!
I recently got very excited at the local Home-Despot when I found out they sold glow in the dark paint! I've painted a few things with it (including various parts of the kids - which was more their doing than mine!) but nothing really stood out until I realised I could coat ping-pong balls with the stuff, drill holes in them and insert LEDs where er... "the sun don't shine". I figured, periodic pulses from the LEDs should be sufficient to charge up the paint on the balls and make them glow.
One of the things that took the longest out of all of this was painting the ping-pong balls & getting them to dry without all the paint oozing off or collecting at one spot. The best technique I could come up with was to dip my balls in the paint and then dance around the room waggling them in the air (this was after connecting the LEDs). Ok, ok, this is getting too much, I'll be serious now. Unfortunately, that really was my technique for getting the paint to dry evenly. I'd tried just painting them with a brush and leaving them on some paper, but all the paint oozed down to the bottom and glued the balls to the paper, but left only a really thin coat on them. Bah. I think I'll look for spray on paint for any future project involving curved surfaces.
The parts list for this is pretty small: an ATTiny13, 5 LEDs, some perf-board, wire, 8 pin socket, some female header pins (single-row), some snappable male header pins (also single row), a battery pack (I used a 2AA pack) and some ping pong balls.
The circuit was easy, now that I've got the hang of soldering. I decided I'd make something a little more modular than normal, so the LEDs weren't soldered directly onto the board. First, I soldered the LEDs onto some wire (cut in pairs to a few different lengths). Then I soldered on header pins to the other end of the wires.
For the circuit board, I soldered on the IC socket and added some female headers. I included a row for all the ground pins as well as sockets for all the active uC ports (no need for the reset pin to have a header and I could have left off pin 8's header too). I used one of the cut-off LED leads to create a ground wire to easilly connect all the ground pins.
I wired up the power leads first - and completely forgot to include a power switch!
I drilled small holes in the ping-pong balls and hot-glue'd the LEDs in place. Then it was just a matter of connecting up the LED/balls to the correct pins. I had marked all the ground leads with a black ring at the base. I've used all wire of the same colour so that, if I make something interesting out of them, the wires won't stand out too much.