I am tasked to build a couple of hand props. They don't have to stand up to much abuse (because they are basically demonstration items for a pencil-and-paper gaming group) and they don't have to have functional electronics (but they will, because that part is fun, and I'm resume-building, and "Will it light up?" is the second-most frequent question asked on The Replica Props Forum. )
I know they need to be delivered by October, and the cost needs to be under $200 each. That is enough to begin planning the planning.
I've decided to use a convergent method to plan these. Since they are basically boxes with some knobs and lights on them, the first question was what kind of planning was necessary for these controls.
There are three basic strategies for controls and similar technical doo-dads an actor has to interact with:
1) Hide the function by using unlabeled buttons, okuda-grams, and similar.
2) Figure out what the controls actually do.
3) Ignore the problem completely.
A hybrid form is when the controls were simply assembled randomly but either fan canon or the actors themselves figure out the specifics of what some of them do. See "Galaxy Quest" for one of the great variations on this.
These being demonstration props for a bunch of technically-minded people, the second option was clearly the only viable one.
So the next question was how much did I need to research before I could make the controls realistic? Fortunately, these are rather peculiar props. Essentially they are techno-magic, and what it boils down to, is they are driven by game mechanics. I don't need to figure out how a real-world device might detect a variety of radiological threats and display them; I needed to figure out the most efficient yet interesting button layout for a "I cast a 'Detect Radiation' spell on the room."
In case you hadn't figured out, the game in question is the Morrow Project. The devices are the CBR kit and the Med Kit that are carried by individual Recon Team members.
Which means the practical functionality is well supported by the "I'm just a game mechanic" nature as described in the rules. They have much larger and more sophisticated devices to give them detailed information about CBW threats or to deal with medical problems. The primary and sole significant function of these particular devices is to flash a light when there is a threat, and administer a one-dose-fits-all cure when appropriate.
In the real world, a portable detector would need all sorts of ways to adjust it and tune it, and there would be long lists of exceptions and false readings. In this case, although the boxes are vintage 1970's military olive-drab, what is inside comes From the Future. So we aren't saddled with the realities of test sources and calibration knobs and filters that need replacing. It just "works."
And that removed the need to actually learn anything about real-world radiological threats and the detectors thereof. All I needed to know is that a big light would light up when there was "bad stuff." The details were inconsequential, and the actual prop did not include any of them.
What largely remains is developing the construction method. I still haven't completely planned the plan. I've sketched possible control layouts, and researched possible components. What I believe is that at some point I will be able to create a scaled drawing. What I don't know yet is how far I will need to plan before I can order components; much depends on how accurate the dimensions need to be, and if I can get those accurate dimensions without the actual parts.
I am looking at using VFDs for the displays. The expanded description I am working from posits 7-segment displays, and in the period in which the external case is made displays are moving away from LED (although the brighter green LEDs are used in a couple of places as a replacement for the old red ones), and old-style LCDs are becoming more common. VFD's are the cutting edge for "cool," and found mostly on applications where plenty of power is available (aka rarely on hand-held devices).
But there are external constraints. Old-style LEDs are hard to find. They are also dim, and although this is a more accepting audience than the usual, there is always a degree to which you want to skew reality to better fit modern expectations. A simple red seven-segment, or LCD, doesn't have the "cool" factor of a blue-green glowing VFD.
On the other hand, the VFD requires more work to supply the right power and to interface with.
In ranking of simplicity, the ways of accomplishing the display are something like:
1) No display at all (aka just a blank faceplate).
2) Static display; an image with a light source behind it.
3) Modern LCD display or OLED. The latter in particular has potential as basically pretending to be some class of older display, although the pixels are liable to give it away. The prime difficulty with the former is that most modern LCDs are supertwist, designed to be used with integral backlighting. They are also almost entirely 2-row type, PLUS the standard form factor is simply too long to fit on the box!
4) Color OLED or LCD, displaying image of an older display.
5) 7-segment LED constructed from modern modules
Since I don't really know enough to plan at this stage, I may have to break off getting a dimensioned faceplate design together and instead work on lighting a prototype display.
And that's about as far ahead as I can work. Any more planning is liable to be in error. So the plan of the plan is to stop planning at this point and start experimenting!