I chose to reverse engineer a Tamaguchi toy – an electronic pet. It’s a simple toy with a just a few buttons, a monochrome LCD screen and an incredibly annoying speaker. I believe the construction process for this specific Tamaguchi is completely manual labor.

Deconstruction

On the back it has 4 screws which hold the two plastic cover pieces together

Plus one extra screw to hold the batteries encased

The buttons operate by pushing a conductive piece, embedded in the rubber button, onto the PCB where it closes the circuit

The PCB design is very simple: an MCU in the middle, and all the components simply connect to it. The whole circuit is working off the 3×2=6V (?) the two coin batteries provide.

Assembly

The display fits into the socket in the plastic. The buttons fit on the buttons hold.

You screw in the PCB that secures the screen and buttons in place, and the speaker press-fits into a holder in the back plastic cover. Then simply cover with the back plastic and screw it in. Batteries go in the sockets and covered by another plastic cover.

List of parts

• Plastic: front, back, battery cover and button hold (injection mold, 0.50$?)
• PCB (single layer, simple, 1.00$?)
• Tiny speaker (1.00$, from digikey)
• Display (1.00-2.00$, from digikey)
• Rubber buttons x4 (0.50$?)

Total (may be): $4 – $6 ?