Circuit Bending a Vintage Speak & Math

The Speak & ___ line of educational toys from Texas Instruments was noteworthy for its popularity, but also for being among the first low-cost devices to feature speech synthesis. In this Instructables tutorial, Kevin demonstrates how to circuit bend a Speak & Math to generate intriguing sounds perfect for lo-fi music production.

The Speak & Spell, Speak & Math, and Speak & Read all used the legendary TMC0280/TMS5100 from Texas Instruments, which was almost solely responsible for making speech synthesis affordable in the late 1970s and early 1980s. The technology is fascinating, but to understand this project you just need to know that the chips synthesize speech by generating tones to build phonemes and then words.

If you want to know more about how that works, I made a video about the Sears Talking Computron that uses the same chip:

The theory for Kevin’s Speak & Math circuit bending modification is simple: the addition of a variable resistor makes it possible to adjust the frequency of the speech synthesis chip’s oscillator. Decrease the frequency and you lower the generated pitch. Increase the frequency and you raise the pitch.

Here, Kevin used a Spectra ThinPot linear potentiometer for the variable resistor. That is nice, because it is unobtrusive and lets the user adjust the pitch by sliding their figure across the surface.

After performing the modification, circuit bending is easy. Just activate some function on the Speak & Math so it starts talking, then move your finger across the potentiometer strip to tweak the speech synthesis pitch.

Combine that with a sick drum beat and looper, and you’re off!