Perhaps the most iconic 80’s music toy was the Magical Musical Thing from Mattel. The TV commercial featured a kid playing melodies with one finger on the toy’s keypad strip — and finishing by playing it with his head! It featured a sound circuit that was designed around the cheapest and most basic building block of digital electronics: the 4049 CMOS hex inverter chip.

Usually used for decoders and multiplexers, the lowly 4049 was re-imagined by Mattel’s thrifty engineers to create musical tones. Three of the IC’s six logic gates were linked head-to-tail with a resistor and capacitor to create a simple, self-oscillating on-off/on-off square wave generator. The output of this oscillator was hooked up to the remaining three inverters in parallel. Their combined outputs were just enough to directly drive a speaker, with no audio amplifier needed!

A network of resistors created the various musical tones. This was done using a cleverly designed membrane switch pad. The top and bottom layers were made from a single, folded piece of Mylar, printed with conductive silver traces connecting strips of resistive paint. The middle layer was a die-cut insulated spacer with holes positioned to make touch points, each labeled for a different color-coded musical note. Touching the membrane pressed together two conductive strips, which completed the circuit through a path of resistors, producing a single musical tone. The shorter the path, the less electrical resistance, the faster the circuit oscillates, and the higher the pitch! Beep boop! Follow the color-coded notes to play a song or slide the “Thing” over your body for a flourish of notes.

Now you can make your own custom version of this classic 80’s toy. Wire up the circuit, paint a membrane keyboard, and make a housing (or put it in some repurposed container). This DIY re-do has a new added feature: a circuit-bending touch point.

Download the templates.