Markus Wobisch

When watching the trailer for the new Wes Anderson movie "Asteroid City", a few things caught my eye: In the first place, of course, the beautiful colors, then the rangefinder camera (which also got the attention of others), and then ... that wonderful, minimal, mysterious prop (at 51 sec).

"What do those pulses indicate?"

"What? Oh, the beeps and the blips? We don't know."

If you ever visited my blog, you may have noticed that I love building movie props with light and sound effects. So, naturally, I started thinking about how to build this one.

The first step is always about collecting all available information. So far these are the images from the movie trailer, plus one other image that I found on the web.

The eight digits are updated from the left to the right in 0.1 sec intervals, and then the display stands for half a second (I got that from counting frames in the trailer).

In another clip, one can see the following two patterns alternating - this looks like a warning/alarm signal.

The left one is blinking three times and then the right one is blinking once. (They are on for approx. 2/3sec and off for approx 1/3sec).

Getting the Dimensions

With these images, I think, I captured all the different light patterns that can be seen in the trailer.

To estimate the size of the prop, the perspective in the lower images helps to use the chair as a reference. Comparing this to my office chair, it seems that the prop is about 2 feet wide.

With this in mind, I use one of the upper images to look at the details.

And it seems to make perfect sense that the spacing of the lights is one inch (which makes the spacing between the eight modules 2"). With this, the prop should have a width of 24 1/2" and a height of 7". The two feet have a distance of about 16" and a width slightly less than 1" (consistent with the thickness of 3/4" of typical pine boards).

The Electronics

The whole unit will be operated by an Arduino Pro Mini microcontroller. The lights are operated by power shift registers TPIC6B595 which can sink up to 150mA for each channel. Based on the following image, I think that regular (5mm) LEDs are too small.

But 8mm straw hat LEDs look much better (and the "straw hat" type provides a wide viewing angle). With 1" spacing, the six LEDs of each of the eight digits fit one 5cm x 7cm PCB.

And they can be very bright (0.5W / 150mA). I will, however, not operate them at full brightness. With current-limiting resistors of 68 Ohms, each LED will draw about 30mA and still be bright enough to be visible in a bright environment. If (on average) 24 out of all 48 LEDs are on, the whole unit will draw 0.72A - this is what typical USB chargers can easily provide.

By connecting the "enable" pin of the shift registers to one of the Arduino's PWM pins, one can later reduce the LED brightness as required.

Building the Enclosure

The enclosure is built from 3/16" plywood using a laser cutter. It is designed such that the front plate, the top and the sides do not have any slots or tabs, to avoid having to spackle and sand those. Only the bottom and back piece feature slots and tabs.

I start, mounting the enclosure base plate on a foot. If we assume that the unit in the movie is placed on ground level, that foot would be about 3 feet tall. However, since I would like to keep this not too large, I will make the foot 1 ft tall. This way, it can sit on a desk or a shelf. The foot is made of two pine wood 3/4" x 3/4" square dowels screwed and glued to a 1/2" plywood base.

Fresh from the laser cutter: the other pieces for the enclosure.

The choice of the paint colors is not easy, as the images from the movie trailer are not taken in natural light. While the front plate is clearly black, the outer sides may have some color. But I assume that this comes from the light conditions, so I decide to paint the outside white.
To avoid painting at the boundaries after the unit is assembled, I paint the front plate and the edges of the bottom/top/sides before gluing. Then, the back plate is glued to the three pieces that provide the internal structure. The whole thing is glued to the base, and the front plate is added.

Then, the sides and the top piece are added and everything is painted.

Little spacers are added behind the front plate for mounting the PCBs of the LED boards.

Assembling the Electronics

The electronics is distributed over 9 PCBs: One that has the Arduino and eight for the LEDs for each digit. In the first step, the LEDs are soldered in place using the openings in the front plate as a guide.

Then I finished the PCB for the Arduino, and two of the LED boards.

I wrote some test code, and (surprisingly!) it worked.

Then the other six LED boards are finalized, ...

... and the whole unit is assembled.

Before watching the movie, I can only rely on light patterns that I saw in the clips on the web. So, I programmed the Arduino to display random light patterns, randomly between 12 and 30 times, and then once the "alarm/warning" pattern (as mentioned above).