How Singing Fish Work

Inside the Plaque
The circuit board -- the "brain" of the fish
The circuit board -- the "brain" of the fish

Inside the plaque there are five different components that control the fish:

  • A printed circuit board containing the controller chip as well as the motor and sound amplifiers
  • A speaker
  • A photocell to detect movement
  • A battery pack
  • An on-off switch

The photos below show these components in detail. Here is the logic board -- the "brain" of the fish:

The circuit board contains an integrated circuit (IC) that controls the motors and also contains the songs in a digitized format (see How CDs Work for information on digital music storage). There is one minute of music on the chip, although it is not the highest quality. There are probably 8,000 samples per second at 8 bits per sample stored on the chip, or almost half a megabyte of data! The chip synchronizes the movements of the mouth, tail and body to the beats of the music. It does this by sending carefully timed, short bursts of power to the electric motors. The transistors that you see on the circuit board amplify the chip's signals so there is enough power to drive the motors (or the speaker).

This electric motor on the back side of the skeleton swings the entire front end of the fish out from the plaque, toward the viewer. Once again, a spring is used to return the front end to its original position once the motor stops. There is a photoreceptor cell near the bottom.

Whenever a person or object passes in front of the fish, light is blocked from hitting the photoreceptor. The photoreceptor then sends a trigger to the IC telling it to begin. Also wired into the circuit board is a manual pushbutton switch, located just above the photoreceptor. This switch does not cut power directly -- instead it sends a signal to the chip. If you try to turn the fish off in the middle of a song, the fish will actually complete the song before turning off!

This small speaker on the back of the plaque reproduces the music sent to it by the IC. The battery compartment contains four C batteries, and there is a plug for using an AC adapter.

It is true that a singing fish doesn't do anything useful, but even so it is a pretty amazing piece of technology!