Now that I have a tentative plan for how I’m going to control all 300-some LED segments, the next step towards making this prop a reality is to figure-out the specifications for the LED displays.
The Original Prop Displays
I’m going to start, as you’d expect, by looking at the original film props.
This image should be familiar by now. This shot is the first time the audience sees the time circuits and is what everyone thinks of when they imagine “the time circuits” from the films. These are the ‘C’ car time circuits.
7 Segment Displays
The 7-segment displays used in the film are likely off-the-shelf electronics parts. They were commonly available at the time the film was made, and there would be little reason for the props department to build something custom. Diegetically, it would make sense for Doc to buy stock displays as well. This is supported by the visible decimals on each display, although they are unused in the films.
If we enlarge that photo, we can see that there are faint white lines between each digit. This shows that each digit is a separate component. Again, this makes sense for both the prop and the “real” time circuits: one part makes the wiring the exact same for each digit, and limits the numbers of different parts needed for each display.
You’ll also see that the “font” used for the displays is hard-edged, unlike some modern 7-segment displays which have rounded edges. The displays also have a black face.
Alphanumeric Displays
If you look closely, you’ll see that the alphanumeric displays aren’t LED displays at all. In fact, they’re small pieces of glass masked off to look like proper displays with an incandescent light bulb behind them.
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