So, all the parts are made as a prototype. At this point I had about two days before I was skipping town to spend christmas with my family (as was my girlfriend) - so I needed to get this finished fast. Please forgive the lack of photos of the builds!
Putting together a circuit:
I didn't want to have to use up the Arduino shield to make this and decided to make the power supply, motor control circuit and Arduino circuit all on one piece of veroboard. This is another bit I don't have a photo of :( - so here's the circuit diagram:
That's all there is to it really! Surrounding the voltage regulator is a chunky heatsink. This is mainly because the RasPi and GPRS dongle combined happily much through about 800 mA of power. Given that there's a 2v drop across the regulator that (2 * 0.800) = 1.6w of power that's being dissapated across it. On its own it will get incredibly hot, so a heatsink does a good job of bringing it down to a good temperature.
The last thing I took a picture of before finishing it and wrapping it all up was the many iterations of the clock face. Originally I was going to laser cut the dial out of MDF and print the design onto paper but there was just no time! It was back to good ol' handwriting and drawing that saved the day!
(The amount of random junk on my desk is worrying)
The body itself was an old chinese clock from a car-boot sale in Vauxhall. It was pretty beaten up and needed new feet. I removed the original mechanism (and sold it on eBay!). I discovered that spray-paint is wonderful and made a nice heavy board backing for the face that hides some of the workings. In this photo you can just about see the circuit board that I made for the Arduino and motor driver.
And so that's it! She got it on Christmas day and was working - checking in every minute with my webserver until the begining of February when it got moved next to a wall. Unfortunately the mobile broadband stick doesn't seem to be able to pick up and maintain a solid connection there - and it's location at the bottom right of the clock under the pi and pi-plate probably doesn't help. Even worse, the Pi doesn't know to try to reconnect if no connection is detected. I wrote a simple script to try and fix this but it's not really helped much. Fortunately however, the mobile broadband stick contains a connection for an external antenna. I'm about to order one and install it when I'm next visiting, although maybe having a GSM antenna stuck out the back of it might take away from the magic - it'd be good to have it reliably working again!
The next step is to figure out a way of always getting it to update correctly, instead of trying to use the terrible webapp I made on my iPhone. Perhaps attaching a modem and arduino to my bag or car?!
Also, although I'm not really all that familliar with the Harry Potter series, the idea of trying to make magical items real is kinda fun! I'm thinking of a way to use skills from my day-job (computer vision and graphics) to make something, maybe even the Mirror of Erised ? Yeh, I get a feeling that one might be expensive. And need more time than a few weeks before christmas...
Anyway - if you've got this far reading, thank you very much! Please please please leave comments, questions, corrections etc and I'll try and get back to you...
Again, massive thanks must go to the London Hackspace and its wonderful community for the inspiration and encouragement to go for it, and think of new ways to solve problems and setbacks.