I can try. These are the cards that, when you open them, play a short tune.
There is a small electronic circuit embedded between the layers of the card. The main components of this circuit are a silicon chip, a battery, a switch, and a speaker.
The switch is a push button that activates the circuit when you open the card. This is called a "normally closed" switch because when it is pressed, the switch is off. When it is not pressed, the switch is on. Closing the card presses the switch, turning off the music. This works like the light switch on your refrigerator.
The battery powers the circuit. Without a little bit of electricity, the electronics can't work. It's like a watch battery, small and thin, and not replaceable without a soldering iron.
The speaker is just like the speaker on a cell phone, only smaller. It produces sound by vibrating the air with a small diaphragm. An electromagnet or a small crystal generates the vibrations. The speaker is small and as a result cannot reproduce low notes because it can't move enough air to make sound at these low frequencies.
The chip (at least in the one I dissected years ago) is a custom integrated circuit designed and built specifically for this purpose. It contains (a) some read-only memory containing a digital form of the musical tune, (b) some logic to convert the digital form of the music to a signal that can vibrate the speaker, and (c) some timing logic to step through all of the data in the digital music from beginning to end.
The memory part of the circuit holds the music data in a format similar to an mp3 file or like is what is stored on an audio CD. Using a music box as an analogy, this data is like the bumps on the rotating drum in the music box.
The timing logic is like the spring in the music box, rotating the drum so that the bumps all pass, in sequence, the music mechanism. This logic reads the music data "note by note" (though the data is probably not stored strictly speaking as "notes") and passes it to the music generator.
The music generator is like the vibrating tines in a music box, converting the discrete music data into voltage signals that are changing up and down quickly which, when fed through the speaker, cause the diaphragm to vibrate, making the sound.
These cards can be made cheaply because the chip, once designed, can be mass produced, driving the cost down to pennies each.
I actually own a company that sells the sound modules (or music chips / voice chips) used to make your own greeting cards. It's pretty simple to record or program your own modules. I even made some videos showing how this is done. Here are some links showing how this is done, how to make your own musical greeting cards, and how to purchase. We even put lcd video screens as well as webkeys and NFC tags (near field communication, rfid) in greeting cards, brochures, and invitations and sales folders as well.
Prerecorded sound modules, and video lcd screens (with a sound or video you provide) and custom printed cards and invitations. Mainly for events (personal or business), and marketing purposes.
Please share your thoughts as we are trying to expand our business.