sphaleron: The Light Box: A DIY STEM Toy

My niece, age two, is obsessed with lights. Entering a room, she will point at each fixture saying "light! light! light!" until you turn them all on. I think she keeps a complete mental inventory of every light-producing object she has encountered. She learned very early on that she could control the lights using a wall switch. This got me thinking: what kind of action-at-a-distance magic must this look like to a two-year-old? A lot of things must seem like magic!

I am an experimental particle physicist, so trying to make sense of the natural world is sort of my job! In that spirit, I set out to build a toy for my niece which would build upon her natural curiosity and ideally help teach something about the universe.

💡 "The Light Thing"

The idea is this: a set of light switches controls a set of lights, but the connection between them is through a set of patch cables which can be rearranged like a switchboard. The goal is to emphasize the physical connection between the switch and lightbulb, and provide a simple playground for experimenting with circuits.

A few design constraints: it has to be super safe, it has to be uncomplicated, and the switches and bulbs have to be the real thing.

I imagined a sort of console, which would sit on the ground or a table:

Concept art

Construction Phase

Fortunate indeed that the audience is a two year old... I am no carpenter. But really, a drill, screwdriver, small hand saw, a keyhole saw, and something to measure with are the only essential tools.

The first step was laying out some parts to get a sense for what size would really work. It had to fit three ceramic sockets across, at least, but how much room for the patch cables?

Trying it on for size...

Somewhat arbitrarily, the footprint is 21" x 17" and it tapers from 8" down to 2.5" in height.

The box consists of a wood frame built from 3/4" square dowels cladded with 1/4" oak plywood.

The frame

With the frame ready to go, it's just a matter of cutting the plywood to size, cutting rectangular holes for the light switches with a keyhole saw, and drilling holes for the light switch wires (under the ceramic sockets) and the 1/4" jacks for the "switchboard."

A partial assembly

The Lights

Perhaps the most straightforward way to do this would be to actually power the lights on 120V AC coming in the back, and the switches and patch cables just carry a small signaling voltage to a relay that actually turns the light on.

However, in order to be super safe, and also to make it portable, I decided to make the whole thing low voltage. But still the lightbulbs had to look like real-world/grown-up lightbulbs. So I ripped apart the lightbulbs and did my own thing inside. With my Sylvania #74311 bulbs, it turned out to be possible, if tricky, to do this without completely destroying them.

The original insides

I carefully pried off the dome and removed the board, yanking out the HV board behind it in the neck of the bulb. The ground and hot wires weren't soldered in, they were just held in place by pressure -- by the screw threads on the body for the ground, and the electrical foot contact which is just a pin that pops out. In 1 of 3 cases, the ground wire didn't pop out and I didn't have to remove the screw threads, which really made things easier.

Reusing the original board as a structural base, I replaced the whole insides with a set of three bright white LEDs in parallel plus a 100 Ohm resistor, on a little perf board raft. This part could certainly be improved a lot, in particular to make the illumination more uniform, but gets it close enough.

The new insides

At this point I also sanded off the regulatory markings, which certainly no longer apply.

Wiring

With the modified LED bulbs in hand, the rest of the wiring was straightforward. After staining the cut plywood a nice dark walnut and putting on a few coats of Polycrylic, I wired up and installed the sockets and switches, and installed six 1/4" mono jacks (as for an electric guitar, but long-shafted ones that can make it through the 1/4" plywood).