Color-Changing Cuttlefish Card With Chibitronics

This light-up paper circuit uses multiple reed switch sensors to simulate an animal's ability to blend in with its environment. I chose the cuttlefish, a member of the cephalopod (squid and octopus) family, because it's famous for almost instantaneously disappearing into the background. (Unlike the chameleon, which apparently changes color on a whim.)

A reed switch is a type of sensor that reacts to magnetic fields. A "magnet on" reed switch closes the circuit by causing two fibers inside it to connect. When a magnet is near, it turns the LED on. When the magnet moves away, the LED shuts off.

The cuttlefish on the card holds a small magnet. As it "swims" around the ocean scene, it can activate the different colored LEDs, one at a time. In open water it glows blue. As it passes a bunch of sea grass, it shifts to green. And when it nears some coral, it turns pink.

For the lights and power, I used nicely-robust Launchpad LEDs and battery from Chibitronics. They have metal tabs which attract the magnet. When not lit up, the cuttlefish can be parked over the battery (which is encased in plastic and which meets current safety regulations regarding coin batteries). I also used Chibitronics free, online Circuit Sketcher software to lay out the circuit.

You can find more info about Chibitronics' Launchpad products, and paper circuits in general, at https://chibitronics.com/your-first-paper-circuit-revised-launchpad-led-battery/.

2 sheets letter-sized cardstock (8.5 by 11 inches)

printer and/or markers

Conductive Fabric Tape

Conductive Fabric Tape Patches

Chibitronics Launchpad LED Variety Pack

Chibitronics Launchpad Battery

Chibitronics Reed Switch -- Magnet On

small (8 mm) neodymium craft magnets

small adhesive dots

Double-sided adhesive foam strips and cubes

(WARNING: Coin batteries and small disk magnets are a swallowing hazard for children.)

My template fits on two letter-sized sheets of cardstock. When cut apart, I get three layers:

1. the base of the card to hold the circuit
2. the ocean background, to be colored in and placed on top of the circuit layer
3. the cuttlefish, to be moved around the colored background layer

For the base of the card, I sketched out the ocean background on the bottom half of my canvas on the computer. (I'm not fancy, so I use Powerpoint's draw feature as my graphics program.) The top half was left blank, so it could be folded behind for the inside of the card. This became the template on the first sheet of cardstock.

I sketched the cuttlefish separately. Then, for the the second sheet of cardstock, I duplicated the background and added a duplicate of the cuttlefish. This gave me a rough idea of the size the creature should be. I was still able to adjust everything once I added the circuit in the next step.

My cuttlefish environment contains green, blue, and red LEDs in parallel circuits. That means each LED connects separately to the battery. Each LED also has its own reed switch sensor that turns it on when a magnet is near. My main concern was to make sure the reed switch sensors were far enough apart that the magnet would only trigger one LED at a time.

I started by positioning the battery under the sandy sea floor, so the cuttlefish would have a place it could be its pale self. Next, using Chibitronics' free, online Circuit Sketcher software, I laid out the LEDs and sensors and the lines of conductive tape that connect them. That made it possible to move the components around to get the optimal distance between them.

A couple of tricks that were helpful for this particular Circuit Sketcher design:

1. There was no reed switch sensor available in Circuit Sketcher (it is currently marked as "pending" in the list of suggested updates), so I substituted cut-and-fold switches. This let me test that the circuits were working as I moved things around so I didn't accidentally create any short circuits.
2. I uploaded a separate image of the cuttlefish so I could move it around and check how it fit with the circuit.
3. Once I was happy with the circuit layout, I made a duplicate of my whole Circuit Sketcher project and swapped in images of the reed switch so I could print out a template that showed how the actual sensors fit into the circuit. That way I still had the original in case I had to go back and make any big changes.

For help getting started with Circuit Sketcher, go to: https://chibitronics.com/2025/08/25/try-circuit-sketcher-design-software-for-paper-circuits/

When I was satisfied with the templates, I printed them out. (Note: To make the circuit easier to see in the photos, I used a printout of the plain background, without the circuit markings.)

To build the circuit, I first positioned the components. Then I ran the tape from one component to the next. The tape went right over the the metal tabs of the components, both to make an electrical connection and to hold them in place. Where needed, I used little conductive fabric patches to connect the wires on the reed switch sensors to the circuit.

For the cuttlefish, I printed and cut out the drawing. Before finalizing the position of the magnet, I tried it in several different spots on the cuttlefish's back. I got the best results with the magnet beneath the cuttlefish's eye. I then attached it permanently with an adhesive dot. (You might want to use something stronger.)

Finally, I ran a strip of thin double-sided foam tape all around the edge of the cuttlefish's underside. This lifted the piece away from the background, which helped diffuse the light and kept it within the boundaries of the cuttlefish's body.

Before I finished coloring in the upper layer of the background, I decided to poke holes above the LEDs, to let more light shine through and reach the cuttlefish.

I marked the spots for the holes by pressing the background down against the Launchpad lights. The LEDs made little bumps in the paper.

Then I used a small sharp tool (in this case, a tiny screwdriver, but a pencil point or toothpick would also do) to make a hole through the bump.

For added diffusion, I covered the back of the hole with a piece of opaque plastic tape.

Finally, I attached the colored layer to the circuit layer using double-sided foam tape cubes in the corners and around the edges.

All in all, I was happy with the way my cuttlefish environment turned out! What kind of design would you make with this layout?