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