Create Shell

Wrap a ball in a layer of thin plastic. A large mixing bowl also works if a ball isn't available.

Cover in successive layers of clear masking tape. Build up about 6-7 layers of tape, or until the shell feels thick and sturdy.

Please be careful in using sharp objects to cut items and adults should assist younger makers.

Cut in Half

Use scissors to cut around the middle, creating two halves.

Create your desired shape

Cut the two hemispheres into football shapes by trimming some material off each side along a curved line.

Cut some indents into the top, bottom, and back of the fish shell. These indents will provide openings through which the fins can stick out.

Fisheye Hole

To give your fish a glowing electronic eye, we'll cut a hole in which to install the Circuit Playground Express board.

Trace outline of CPX on the inside of the fish shell.

Use diagonal cutters to cut a hole, staying 1/4" inside the outline. 

Trash Fins

Use pipe cleaners and masking tape to create some fins for your fish.

Sandwich a trimmed array of pipe cleaners between two sheets of masking tape.

Trim around the edges to achieve the desired size and shape.

Set these fins aside, they will be glued onto the the fish in the final steps. 

Fish Frame

Create a frame to hold the fins using a piece of scrap cardboard.

Place a section of a plastic straw over a piece of wooden skewer. Use hot glue to stick this to the frame. 

Hot glue can burn skin and should not be used such that it might create a fire hazard. Please assist younger Makers with this step.

Fin Hinge

Glue a small length of plastic straw onto the hinge.

Next, use hot glue to add some paper fin supports at 90 degrees to the straw attachment.

These paper supports will serve to hold and stiffen the fish's fins when the time comes.

Prep Servo

Unbend a paper clip and create an "L" shape.

Screw the wheel attachment to the servo horn.

Glue the section of the paper clip onto the servo wheel.

Install Servo

Cut a hole for the continuous rotation servo motor and glue it in place.

Poke three straws onto the paper clip. Trim each straw so they extend just an inch or so beyond where they will connect to the fins. 

Final Connections

Cut a small slit down the middle of the straw. Use hot glue to clamp it around the other straw. 

Do this for each fin, then use some hot glue to affix the fins to the paper fin supports that we added earlier.

Your frame should now be ready to install inside the fish shell!

Install Electronics

Use hot glue to tack the Circuit Playground Express in place inside the fish.

Loop your strip of NeoPixels around the inside of the fish shell, holding each end in place with a liberal amount of hot glue.

Finally, bring the two halves of the fish together, enclosing the electronics inside.

Use some large dabs of hot glue around the outside edge to hold the halves together. Glueing a JST extension power switch to the underside of the fish can help make it easy to turn on and off.


Problem: My motor doesn't turn!

Solution: Make sure that your Circuit Playground Express is connected to a power source (anywhere between 3V-5V is safe). If you're using a AAAx3 battery pack, check that the switch on the battery pack is set to "ON".

Problem: My Circuit Playground Express doesn't show up as CPLAYBOOT


  • Be sure you have a Circuit Playground Express.  The Classic will not work with MakeCode.
  • Some USB cables are "charge-only" and won't pass data. Try using a different USB cable and try using a different USB port on your computer.  
  • With the Circuit Playground plugged into your computer with a micro USB cable, click the small reset button in the center of the board. The lights should all turn green. If they don't, try double-clicking the reset button.

If things still aren't working, head over to the Intro to Circuit Playground Express guide for more suggestions.

Motor Speed Adjustment


If you find your motor doesn't come to a full stop, you can fix this by making tiny adjustments to the potentiometer on the bottom of the motor.

This guide was first published on May 31, 2019. It was last updated on Mar 08, 2024.

This page (Trash Fish Assembly) was last updated on Mar 08, 2024.

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