I've been putting in some effort in the electronics on the project, and figured it was as good a time as any for an update.
My brother has some experience building replica props, so I asked him if he could get me some measurements. Actual size isn't a big deal for me, as the size I'm going to make this depends on the size of the displays I will use, and I figure I can just scale everything else relative to the displays.
Speaking of displays, I have been doing a ton of research. there are 7" displays for $15 available online, but buying 8 of them would cost more than I want to put into this (at least right now). There are also guides on how to build huge 7 segment displays, using an array of consumer LEDs or LED panels, but those would require a lot of work. 1" displays are only 1-2$, so I decided to experiment with them first.
I bought all the electronics online the other day, from a wholesaler named Jameco. I made a list of what I'm using right now:
Arduio UNO - $29.95:
LED Controller - $7.95
7 Segment Display (red) $1.25 (x8) - $10
10µF electrolytic capacitor $0.06 (min 10) - $0.60
0.1µF ceramic capacitor $0.15 (min 10) - $1.50
Current limiting resistor $0.03 each (min 100) - $3
Rocker switch - $0.39
This is not a final list, just what I need for a countdown clock prototype. The arduino is rather expensive, but I probably will switch to a cheaper equivalent once I get all the kinks out (the arduino is designed for prototyping, makes the process much easier). We also need some way to enter a start time in the clock, which I could do with a menu and a few buttons, but I have other ideas. And, of course, there's lighting all the other bits to think about.
The only real problem with the clock circuit, right now, is that its time is based on the arduino. Some people have reported a time drift of >20 seconds a day with standard hardware. Also, it doesn't have a battery backup, which is a
key part of the joke for me. I'm pondering getting a clock module
such as this, which has reasonably good accuracy, or the
chronodot which users report has a drift of 2 seconds a year.
My parts should get in over the next couple days, but I'm going to hold off soldering together anything until I know my dimensions. Hopefully I can get something working over the weekend.