Use piezoelectric ceramics to produce sound. The sound-producing principle of musical greeting cards is to use piezoelectric ceramic sheets to produce sound. Piezoelectric ceramic sheet is a special electronic component with a piezoelectric effect, that is, when an external force is applied to the piezoelectric ceramic, a voltage is generated, thereby driving a current. In the musical greeting card, the piezoelectric ceramic sheet is placed in the sound-generating device. When the greeting card is opened, the piezoelectric ceramic sheet is acted upon by external force, generating voltage and driving current. This current is used to drive the sound membrane in the sound-generating device, causing it to vibrate and produce sound.

At the same time, the metal pieces in greeting cards are also used to control the on and off of current. When the metal piece is inserted into the sound-generating device, the circuit is connected and the piezoelectric ceramic piece produces sound; when the metal piece is withdrawn from the sound-generating device, the circuit is disconnected and the sound stops.

Therefore, the sound-producing principle of musical greeting cards is to use the piezoelectric effect of piezoelectric ceramic sheets to produce sound, and to control the playback and stop of the sound by controlling the on and off of the current.