The party boat activity prompt was just to take a bunch of outputs and link them together in a way that might stimulate some sort of organism.

Basically, it’s just use a combination of natural and digital materials to make a thing that makes noises and flashes lights and things like that. While digging through the boxes of components, we found one of these thumpers (solenoid from SparkFun) that moves a shaft when a current is applied:

Photo by SparkFun

Hugh suggested that we might be able to use the thumper as a switch, to turn on and off an LED. I immediately latched on to that idea for several reasons: it sounds really fun and weird, it would act as both a switch and an output (noise, vibration), and most of all, it didn’t require a microcontroller to get create some sort of behavior. Using microcontrollers in the NFCCDL (North Fork Citico Creek Digital Laboratory) comes with enough minor problems (writing the software, using up batteries to upload the software, driver issues on the laptop, etc.) that I, personally, wanted to avoid it as much as possible. I also just like the opportunity to design circuits that don’t require them, because it’s a bit more of a challenge for me, given my limited knowledge of electrical engineering.

So we started figuring out how to make the thumper turn itself on and off. I started out thinking that we circuit could constantly supply current to it, but when it thumped, it could short the circuit and turn itself off. That’s the wrong way to do it. It shorts the LiPo, which is bad, and it’s a more complicated circuit, which is also bad. So Andy suggested that we set it up so that whenever it is unthumped, the circuit is completed and it thumps, which breaks the circuit and unthumps itself. Here’s the circuit we came up with:

This circuit is pretty much a single component version of “The Most Useless Machine EVER”. This is actually an interesting short history of the most useless machine, which apparently was first described by Marvin Minsky.

Solenoid trigger causing the behavior

Once we had a good idea of how to make this thing work, Laura gathered a rhododendron branch and wove some LEDs into the leaves and Hugh whittled a connection point for a little gear motor that would make the whole thing spin while I wired it up and built a mount for the motor so that it could make and break the connection consistently.

The mount for the thumper is a piece of cardboard that I cut off the back of my journal and taped to a mini breadboard. The breadboard has two pieces of copper tape on it (once connected to +3.3V and the other connected to the positive lead of the thumper). The thumper has a piece of tape of copper tape on the end of the shaft that sticks out when it is not triggered that spans the two piece of tape on the bread board, so whenever the thumper is not triggered, its positive lead connects to the positive terminal of the battery. The other lead of the thumper connects to ground, so whenever the thumper is untriggered, it completes the circuit and triggers itself.

Getting that working was really exciting. It made quite a bit of noise and vibration, which was perfect for this project, and I could tune the on/off frequency by pressing the thumper closer and tighter towards the breadboard.

Next we wired up the LEDs to the circuit in a way that they would turn on and off with the thumper (positive leads to the same copper tape as the thumper’s positive lead and negative leads to the ground). We used a bunch of clip wires to do this, which completely avoided soldering or stripping wire. We connected the gear motor to positive and ground so it would spin the whole time, but the branch wasn’t strong enough to handle that and the wires would have gotten all twisted up, so we kicked that bit out of the party.

Late night party boat

We tuned the thumper a bit to make the blinking of the LEDs visible and stuck on the obligatory googley eyes and showed off our creation. It was really satisfying to make something so wild with such a small BOM and labor. Here’s the finished partyboat, the simplest, most useless machine that is actually pretty useful: