I've soldered my 555 pulse generator and my voltage-modifier onto two small pieces of strip board. Here's a couple of photos of the setup for testing the windings on the 5 cores I'll be using for my first full demo.
(the battery isn't in the case, and the arduino is not plugged in because I had started tidying it away before I thought of taking photos).
This one will be a permanent encoding of the word "timui" which visitors to the stand will be able to read with a probe. The next one will be set up for visitors to encode messages into themselves.
Things are really progressing well! I should be back in TOG tomorrow evening and hopefully I can get another 4 of the voltage-modifiers ready to go. It is getting progressively neater, even if that's not obvious from the photos :)
edited to add: I forgot to mention the 9V power supply problem. I was really looking forward to hooking it up and reducing the number of crocodile clips (and amount of fiddling), but when I tested it I realised it was producing 12V. I guess it was mislabeled; that's probably what broke the device it comes from.