So after some late nights hurriedly hacking some stuff together, HAL and I got our stuff together for the haunted mansion. Between work and girlfriend schedules, there wasn’t much time to really polish anything. On the short notice we did a snowy owl that wigs out (eyes fade from green to red and flash menacingly, bird screams and vibrates) if someone comes too close via light sensor, and the man-eating Oobleck blob monster shown here (albeit a less noisy version).
Other pieces there included:
Fairly convincing molded Jell-O brains, sitting on metallic plates wired to a capacitive touch sensor circuit. Every time someone scooped a spoonful (adding capacitance via their body and the metal spoon), the brains screamed! (Or bantered amusingly with the scooper)
A ghost fish that would appear out of nowhere and swim to wherever you tapped on its tank
Too many great things to list; look in the photo album!
There isn’t really much code or reusable design to come out of our projects (other than a new and finally “release-worthy” Blinkenlichten revision, which I will document soonish), just some findings.
Glowstick juice does not mix with Oobleck. It’s oily stuff and it doesn’t smell too nice. (Highlighter juice is water-soluble and does mix with Oobleck; it fluoresces nicely under blacklight.)
Critical specifications for an Oobleck monster: it sits on a flexible membrane, which displaces up and down by different amounts at different distances from the center (obviously, by a lot in the center and not at all where it’s constrained to something else at the edges). The membrane’s active pushing/pulling/flexing of the goo is critical; placing the mix directly on a speaker cone won’t do much (the speaker cone is rigid by design and will just hop the mixture up and down, not flex it). A piece of garbage bag or plastic grocery bag pulled taut over the speaker (creating an sealed-ish air cavity) works well. The membrane should be covered with the minimum amount of Oobleck necessary to create the effect (and/or hide the membrane, if that’s important); it doesn’t take much to completely dampen the membrane’s vibration enough to ruin the effect.
Putting a big angry vibrator bullet in a plush toy does not make the plush toy vibrate around angrily. (If someone reached out and touched it, they could kinda tell that it was vibrating.)
We used the voicebox of the plush snowy owl, which was recorded from an actual snowy owl. It was far more disturbing and eerie than most Halloween toys that make scary noises.
Off-the-shelf toys from Target (we scavenged sensors, and ultimately the whole sensor/amplifier board assembly from one, since it was faster and cheaper than overnighting similar sensors from Digikey et al) are fast and cheap, but the guts are not Designed For Manufacture. (DFM is one of those big buzzwords floating around engineering circles these days, learn it. The idea of making something repeatably manufacturable as opposed to a one-off basement hack repeated millions of times has been around since the Model T and before, but buzzwords make you appear smart.) The circuitboard alone consisted of a custom epxoy-blobbed ASIC mounted on a small daughterboard that soldered at 90 degrees into a 2nd board consisting of all through-hole parts packed very tightly together, possibly hand-stuffed, with dabs of hot glue everywhere holding components in place and taming the sprawling mess of wires leading directly off various points of the board to motors, limit switches, sensors, etc., all of which where glued into place in some complex fashion. The circuit was crammed onto the (single-sided!) board as tightly as possible, despite the tons of empty space inside the toy.