Version 5 (not done):

My goal for version 5 was to make the design manufacturable.

I used eagle to layout and route a PCB, I had the boards made in a shop.

Here's the board with all the parts soldered on. The big cap lies horizontally over other parts to keep things compact.

I accidentally bought bi-color LEDs of the wrong polarity, so I had to rewire the board a bit to get them working (the grey wire).

Here you can see how the whole assembly fits together inside the case.

Here's my first attempt at fabricating an acrylic case by hand. This is where I left off.

You can't really see it in the picture, but I swapped the solenoid out with a much more appropriately sized one. This actually turned out to be quite an ordeal, since I needed a non-standard set of windings. I had to arrange for a Chinese manufacturer to custom make them (long story).

Edit Jun 2021: I've made another version since publishing this. It has a 3D printed case, a new PCB, and it uses a servo for triggering instead of a solenoid. It's been years and I doubt I'll ever commercialize it, so stay tuned, I'll try to post the full schematics in the near future.