Week 2: Press-fit electronic lamp kit

I was interested in using the press-fit as both a mechanical connector and an electrical switch so that users can sculpt a 3D circuit. The simplest circuit I could think of was a coin cell battery and an LED, so I decided to make a build-your-own lamp kit. Electronic components (the LED and the battery) will also be press fit into the piece and I will use copper tape to lay down the traces. The idea of making a press-fit slot for a battery came from James Leng's press-fit earrings project.I also decided to use clear acrylic since light will be able to shine through and bounce around inside the material in interesting ways.

STEP 1: cut pieces using laser cutter

After adjusting the laser cutter settings (power and speed) to cut cleanly through the 2mm acrylic, I started by cutting various-width nitches to see which size produced the most secure press fit. I ended up having to enlarge the notches to accommodate the thickness of copper foil. I then experimented with cutting holes for the LED and battery.

After the slot sizes were settled (down to 0.1 mm accuracy), I designed the actual pieces. For this proof of concept, I chose to design a bare bones kit: 1 battery holder, 1 LED holder, 1 straight connector and 2 corner connectors. All of the corner connectors use 60 degree increments for simple standardization. I basically chose the lengths arbitrarily (whatever looked right) which later turned out to be a problem for contact between the rigid pieces.

STEP 2: add traces by wrapping copper foil

To make the traces, I wrapped the acrylic pieces with copper foil strips. When two pieces are snugly pressed together, the portion of copper at the end of the notches touch and maintains good conductivity (tested using a multimeter). The copper tape was especially useful since even the adhesive is conductive, so that simple sticking one piece on top of another produced a strong connection. For the LED, I simply stuck copper tape directly to the legs (no soldering required) and marked the positive end with an extra piece of foil. In later revisions I would etch the positive and negative signs directly into the acrylic.

I was traveling for most of the week, so I ended up wrapping most of the traces en route to and from New York. It was nighttime much of the ride so I had to use the red LED from my kit as a flashlight, which worked surprisingly well. The process looked something like this:

Here's what the finished pieces look like:

STEP 3: build the lamp!

I built a simple one-LED circuit (the bottom loop) but with more pieces, LEDs and batteries the simple kit allows for far more complex building.

The connections between the pieces are not always reliable which causes a frequent flickering of the LED. This is partially because the lengths of the pieces and slots were measured to fit perfect triangles. Also, I only placed copper tape in the notches so that any slight gap between the ends of the notches breaks the connection. In future versions I would definitely put copper foil around the rim of each piece as well so that contact does not depend so much on how tightly the pieces are assembled.

PDF of cut pieces
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