Markus Wobisch: Building Props for a Back-to-the-Future Time Machine

My other blog posts on BTTF props:

Part 1: Building a Flux Capacitor
Part 2: Building the Time Circuits
Part 3: Building the Speedometer
Part 4: Building the Analog Gauges
Part 5: Building the TFC switch

This is now the last of the Time Machine props that I am building: The "SID panel" (Status Indicator Display) which sits in the DeLorean behind the drivers seat (right from the Flux Capacitor). It does not have any obvious function, but it looks cool in the movie when Marty approaches 88mph and you can see behind him, more and more of the 200 LEDs in this panel starting to light up: One row (= ten) red LEDs, siz rows of yellow LEDs, and thirteen rows of green LEDs. The good thing is that these days LEDs are dirt cheap (like 100 for $0.99 at Aliexpress). The bad thing is that in the original prop, each LED is mounted inside a little plastic holder - and these holders cost like $0.50 a piece (and 0.5 * 200 = ... too much). But I never went for 100% accuracy, so I just omit these holders. With this, I think the whole SID cost me less than $15.

The construction of the enclosure is straightforward.

It was fun, to watch the laser cutter cutting the 200 holes, and the result is, of course, very precise.

Now that the enclosure is glued and painted, it's time to address the electronics. Unlike for the other BTTF Time Machine props, the matrix circuit (and, later, the Arduino programming) for the 200 LEDs is a little more complex.

The LEDs are soldered onto three 9cm x 15cm PCBs, as a matrix.

The electronics is based on an Arduino Pro Mini (ATmega 328). The LED matrix is accessed by a decimal counter (CD4017) for the 10 columns (together with two MIC2981 drivers), and three chained shift registers (TPIC6B595, which can sink larger currents than the 74HC595) for the 20 rows.

The code require a few more thoughts: My SID panel will operate in two modes: 1) standalone and 2) connected (via serial) to the other Time Machine props, so it gets the information of the current speed from the speedometer - and it can adjust the LED activity to the speed.

In both modes, the LEDs are moving randomly up and down. In mode 2) the random activity is coupled to the speed, while in mode 1) a speed value of 40 is assumed. The up and down motion of the individual LEDs columns is, however, not independent. If, for a given column, the two neighbors are higher, this increases the probability for this column to rise. Also, if a column was rising before, the probability is higher for this column to continue to rise in the next step. When a column has reached its max or min value, it will sit there for a while (the time is, again, random) and then change it direction. All the probabilities mentioned here are speed-dependent, such that the overall activity also changes with the speed. At zero speed, the columns are typically only moving up to the 5th row, while at 88 on average more than half of the columns will go all the way up, into the red.

After spending too much time on BTTF forums, I concluded that I had to add some corrugated plastic pipe (of about 3/4" diameter) which is held by two P-clamps (I could not find any purple ones, like in the movie prop, so I had to settle for black), through which the power/serial cable coming from the TFC switch is led.