While everyone else in the country has already moved on from Halloween to some election or other, my brain is still stuck in October 31st. What went well, what needed work, what was scary, what was just embarrassing. I don't intend to pick apart every detail here, but I figure I did owe one final post on one of the big elements of my show. That would be the animated dresser drawers, complete with spooky schematics and demonic diagrams. First though, here's one last tour of the whole room.
Since the undead were otherwise occupied on this night, I had to resort to good, old-fashioned automation components. Making this little effect was a lot of fun and, as it turned out, not terribly complicated, as long as you're comfortable with some very basic aspects of electrical, pneumatic and software design. ...I guess "not complicated" is a relative term here, but I think you'll get it by the time I'm done.
SOFTWARELet's start at the beginning, with the actual brain of the device: the Arduino Uno. This nifty little controller, custom-designed for hobbyists such as myself, is what drives the whole thing. It's literally the same controller I used for my Evil Eye the year before. It runs a very simple program which waits for a semi-random amount of time - between 60 and 90 seconds - and turns on an output which triggers a pneumatic valve. After another two seconds, the output is released and the valve returns to its initial state. A new wait time is selected and the process repeats itself.
ELECTRICALSo far so good. Just one problem. The Arduino is basically just a PIC microcontroller stuck on a board that makes it easy to interface with. The output pins of the controller are versatile, but can only provide 40mA at 5V and cannot directly trigger the pneumatic valve, which needs 75mA at 24V. How to get from one to the other? Observe:
This circuit would probably get me laughed out of most professional outfits, but as with most things, it's the results that matter. What it does is take a 24V power supply and use it for a couple purposes. A regulator knocks it down to 12V to power the Arduino. A transistor is used as the interface between the controller and the valve. When the 5V Arduino output pin goes high, it "switches" the transistor on, allowing 24V to actuate the pneumatic valve. At the same time, an LED lights up indicating the circuit is active. When the pin goes low, the switch is closed and the valve releases.
The other two LEDs function first as a power indicator to let me know that the system is on and then as a "heartbeat". This is just a part of the program that turns the LED on and off once per second to indicate that it hasn't died or frozen.
Here's the what that lovely circuit shown above actually looks like:
|What a beaut!|
Anyway, we've figured out how to turn our pneumatic valve on and off. But the valve doesn't do much in isolation, so we'll need a few more components. I've got an air compressor that I bought a while ago as part of a pneumatic nailer kit from Lowes. This comes with a regulator, which I've set to about 30psi. It turns out this is about the optimum setting for this effect. Any less and the compressor will deplete to and stay at zero when the effect fires. Any more and the air pressure will hit the drawers hard enough to make the whole dresser nearly capsize.
Nylon tubing for the air also came from the Lowes also and the various fittings I needed to hook it all together came from Automation Direct, an online retailer for various components. The pneumatic cylinders which are the heart of the effect came from a local electronics surplus store (as did the valve, for a whopping $1. Hooray for second-hand parts!).
|Two cylinders, nose-mounted to the rear of the dresser.|
|The 24 volt valve. Probably on sale because of a missing/broken|
plastic hood where the power comes in. Still works, though!
Those are all the components. Here's how they all fit together:
There are two different types of cylinders. The bottom one is a spring-return mechanism, meaning I only have to push it out with air and when the pressure is released it'll return to its initial position by itself. The top one is a double-acting mechanism, meaning that I have to supply air pressure in whichever direction I want to push it. This is actually easy to do with the valve I have because it's a two-port valve which is always supplying pressure out of one of its ports. When it's triggered, it simply alternates which port is pressurized. The way this is all configured is such that the drawers move in alternate directions when the effect fires. The lower drawer moves in and the upper drawer moves out, then back again...
...The spirits whisper in their rage. The luminescent, disembodied hands try to get at their demonic possessions in the drawers. The furniture shakes and jumps with their effort. They might not be able to get what's in there, but they just might be satisfied with... your soul!
...Or at least that's how it was supposed to go. As it turns out, repeatedly slamming particle board with 30 pounds of pressure in a small area is eventually more than it can handle. At the top of the evening, the back of the upper drawer broke, which is a shame because that piston had the longer stroke (the drawer came out more) and what I was left with was more a lurching dresser than a finely tuned effect. The bottom drawer continued to work through the night.
In the couple evenings leading up to Halloween I would have this effect going along with the sound and lighting while I worked on other things. I found myself more spooked than I would care to admit, subconsciously, anxiously awaiting the next time the dresser would move, but never being able to acclimate because the timing was just random enough. My wife didn't care to spend more than a couple minutes in the room. My three year old didn't seem to mind at all. I figure with all this exposure to spooky stuff he'll probably be afraid of nothing when he's older. Or everything.
The whole design and construction process for the room in general was a pretty organic one, constantly changing as I came up with new ideas and found new props. The dresser, however, was the one thing that remained the same from start to finish, though, and even if it got mangled before its time, for a while it was looking and working exactly how I envisioned it from the start. I find that more satisfying than than any of the accolades or screams that I heard that whole evening.
Now to start thinking about next year. Maybe something happy and fun?