Dr. Scott M. Baker Gives a Vintage Heathkit H8 Micro a Voice with a Custom Speech Synthesis Board

Dr. Scott M. Baker has been experimenting with a vintage Heathkit H8 microcomputer kit — and decided to build a custom add-on to give the device the ability to talk back.

"A fellow member of SEBHC [the Society of Eight-Bit Heathkit Computerists], Glenn, hooked me up with a good deal on an H8 starter system," Baker explains of his new toy. "It was actually exactly what I was looking for — an H8 that had almost no upgrades, using the original 8080 CPU board and the original tape board."

Originally released in 1977 as a built-it-yourself kit, the Heathkit H8 microcomputer is based around the Intel 8080A processor and runs Digital's CP/M operating system. A modular system housed in a robust case with integrated display and numerical keypad the H8 offered an alternative to the at-the-time popular Altair or S-100 bus systems, with a more robust 50-pin bus design.

Having experimented with the device as-is, Baker set about designing a custom add-on: a speech synthesis board. "The board is designed to use either the Votrax SC-01A or the GI SP0256A-AL2 phonetic speech synthesizer IC," Baker explains of the design. "The Votrax would likely sound better, but is much rarer, difficult to find, and expensive. I have not tested the Votrax support — I only implemented the prototype board using the SP0256A-AL2."

This isn't Baker's first experiment with vintage text-to-speech technology: back in February 2021 he built a board based on the National Semiconductor Digitalker DT1050, a recording-based speech synthesizer tool designed in the 1980s by Forrest Mozer to drive a calculator for the blind; a year later, Baker built a speech synthesis board for the Epson QX-10 portable computer.

A detailed write-up of the project, including a schematic, is available on Baker's website; the board design files and BASIC source code have yet to be published, but will follow in due course.