Yeo Kheng Meng Clones the Classic Covox Speech Thing on a Chip — Thanks to Tiny Tapeout

Analog audio from any PC's parallel port, the height of luxury in 1987 — and now available on a custom-built silicon chip.

Gareth Halfacree
26 days agoRetro Tech / HW101

Self-described maker, coder, private pilot, and retrocomputing enthusiast Yeo Kheng Meng has cloned the classic Covox Speech Thing, with a difference: his is powered by his own custom silicon chip, produced as part of the Tiny Tapeout program.

"When one thinks of designing an Application-specific Integrated Circuit (ASIC) chip, one would typically imagine a very high production cost, lack of access to tools and individuals can’t really do this unless you work in a company or academia," Meng explains. "Thanks to Tiny Tapeout, these barriers are broken down and I managed to have a chip that contains my own design. I sent in a very simple project but it is still my submission no less."

Vintage audio, but not as you know it: this Covox Speech Thing clone is driven by a custom silicon chip. (📹: Yeo Kheng Meng)

Launched by Matt Venn two years ago, Tiny Tapeout allows anyone — whether experienced with silicon design or not — to create their own open-source chip design and have it produced at a very low cost. The trick: each design takes up one or more "tiles" in a shared shuttle, meaning that every design submitted in a given production run is present in every chip made during that run. When you want to run your own design — or someone else's — you can select it from the dozens included.

Meng's submission, made as part of Tiny Tapeout 4 in September last year, is designed to duplicate the functionality of the Covox Speech Thing, a device released in 1987 to convert signals from a PC's parallel port into analog audio. For his custom recreation, Meng eschewed a digital to analog converter (DAC) — Tiny Tapeout, at the time, not supporting mixed-signal designs — in favor of implementing pulse-width modulation (PWM) to create the audio signals.

The resulting board has been tested with both relatively-modern systems — a laptop a little over a decade old, using an ExpressCard parallel port adapter to interface with the Tiny Tapeout test board — and a true vintage system running Microsoft MS-DOS 6.22.

"It is extremely satisfying to have my design baked into physical hardware and working as expected," Meng concludes. "No flashing of microcontroller firmware, computer software or FPGA bitstream. Just fixed electronic circuits doing your bidding."

Meng's full write-up is available on his website.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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