Introduction: Building a "Billie Jean" Sidewalk
Although it's not a scary addition to our Halloween decor, I built a lighted sidewalk (the famous effect from Michael Jackson's "Billie Jean" video) to entertain party guests and treat-or-treaters on their way to our door.
Only the wiring was a little tedious, the rest of the construction was pretty simple, and we've gotten lots of great comments and impromptu dancing.
Step 1: Goals
- Keep any additional platform low to ground. I don't want people to feel like they're stepping up onto something.
- Span the whole 12-15 length of our sidewalk. It wouldn't look too cool if only a few feet were done.
- Outdoor-friendly and fairly immune to moisture (we typically get rain in October).
- And most of all it would have to work with fairly light people, but not crumble under foot of heavier ones. I had to figure people might start dancing on this, so it'd have to take a fair bit of abuse.
Step 2: Choosing Panels and Lights
I considered various light sources- everything from those closet tap lights, to rope lighting. I decided I wanted to stick with low voltage just in case there were any moisture issues; I didn't want to get into putting this thing on a GFCI or something. For the best combination of low power, low cost, good brightness, and instant-on behavior I decided on ultra bright white LEDs. I decided to use just two LEDs per step. In retrospect, maybe using 4 per step would give a more even light spread, but two aren't bad at all and plenty bright.
Next I had to think about the means to make a translucent step that could easily support 300 lbs or more. Acrylic was a pretty easy choice given other materials (like polycarbonate) are either more expensive or harder to work with. I did some crude calculations to determine that 1/2 inch panels would be sufficiently strong if supported on 4 sides. Our sidewalk extends 12 feet from the front door with a 3 foot jog at the end. I decided on using six panels, each 2 feet square, to span the distance. There would be roughly a foot or more on each end of the sidewalk not accounted for, but it'd work out pretty good.
I left the paper layer on what would be the top side of the panels. It was already a decent color and it diffused the LED light very well. It also protected the acrylic, in case I reuse it for a different project in the future.
Step 3: Wiring
Things got trickier though when I had to figure out how to actually run the wiring to have the switches and lights in the desired locations. After folding the schematic around, the circuit for each step became more complicated (second image).
Each step is modular in that each was wired separately, and tested, and later they were all interconnected. Running the wires was tedious. The first step probably took 45 minutes to wire, and each to follow went progressively faster. By the time I got to the sixth one, I was running wire and soldering without thinking and finished it in about 20 minutes.Through testing (the specs weren't published) the LEDs I bought needed around 3 volts. Since the LEDs were in parallel and each step parallel with each other, I found I could run the whole thing off only two AA batteries (in series). I did add a second set of AA's in parallel, just to ensure long battery life, but it wasn't necessary since the bulbs are generally only on for short durations.
Step 4: Cheap and Reliable Pressure Switches
The real trick was thinking of a switching mechanism. I considered micro switches, limit switches, and finally decided to keep it simple (and cheap!) and make a home-brewed pressure switch. My idea was to tape a wire to the upper (acrylic) and lower (frame) pieces of each step with some foil duct tape and separate them with a bit of weather stripping (3/8" thick). The panel sits on top of the weather stripping and as it's depressed, the two pieces of foil make contact and the lights go on. Once the weight is off the step, the weather stripping springs back, and opens the switch.
I decided to place two switches per each step on the edges you walk across. Closing either or both switches would complete the circuit. The good thing about this is that as you're walking along, even if you just catch the edge of the next step, it will light. Having to step in the center of each step would be much less effective.
Adjusting the sensitivity of the switches is easily done by changing the length of weather stripping and how close it is to the foil switch.
Step 5: Framing It In
The last thing to determine was the structure holding the panels To keep the whole thing low I built the structure using 2x2's and 2x4's laying flat. This limited the height to only about an inch and a half. The 2x2's were used to make a square frame to support each panel. The 2x4's were just used to flesh out the sides of the sidewalk to add extra width. I also used a bit of 1x2 sticking up slightly between each 2x2 box to fill the 'gap' that would be between panels.
Step 6: Final Assembly and Results
It takes two people to move the sidewalk into place. Since the acrylic panels essentially rest on the frame, I install them last. One panel at a time I connect the two wires from the panel to the bare wires on either side of the step.
The end result is fantastic. Treat-or-Treaters are shocked when they notice the sidewalk lighting up as they approach the house. The parents are usually the ones who recognize the original inspiration, but even young kids love it without knowing anything about "Billie Jean". We got many excited compliments like "your sidewalk ROCKS" and "this is SO awesome" as they bounded back and forth over the steps.