Dr. Scott Baker's Latest Board Brings Back National Semi's Classic Digitalker Speech Synthesis Chip

A staple of 1980s electronics, the recording-based Digitalker lives again — and, with an ESP8266, even boasts Wi-Fi connectivity.

Gareth Halfacree
3 years agoRetro Tech

Dr. Scott M. Baker has brought back a staple of 1980s electronics, dedicated speech synthesis hardware, by creating a development board centred around the National Semiconductor Digitalker DT1050 chipset — and has even given the resulting device Wi-Fi connectivity.

"The Digitalker was originally developed by Forrest Mozer, with Mozer’s work starting out developing a speech chip to be used in a calculator for the blind," Baker explains of the part's history. "Mozer's design was then licensed to National Semiconductor to become what would be sold as the Digitalker MM54104N and related chips. The ICs bear the name Mozer printed prominently on the IC. The vocabulary is dependent on the ROMs used. If you don’t have the right ROMs, then you can’t say the words you want."

Sadly, many of these ROMs are lost to history - as is the CP/M software application, DTSW500, which allowed for the creation of new speech ROMs from recordings. "This would be the holy grail for Digitalker enthusiasts," Baker explains. "Nobody we know has this software. Several people are actively seeking it. If you do have any leads, then please do share."

Baker's redesigned Digitalker board offers optional Wi-Fi control of the speech synthesis chip. (📹: Dr. Scott M. Baker)

Baker's reborn Digitalker board is powered by a 5V input, with a boost converter to run the Digitalker chip itself, and is driven by a Microchip ATmega328P microcontroller - though that's not the only possible microcontroller on the board. Headers are provided for an optional Espressif ESP8266 ESP-01 module, allowing the board to be addressed via Wi-Fi, in place of a MAX202 level converter which offers more period-appropriate RS-232 access via DB25 or DB9.

The Digitalker IC itself is joined by a 512kB flash chip with bank switching for storage of multiple ROM sets, and an Adafruit audio amplifier with I2C volume control — connecting to one or two speakers of the builder's choice.

For the software Baker has released both the firmware for the ATmega328P and a Python program for controlling the Digitalker over I2C, serial, or I2C — but has not released any of the speech ROMs required for the Digitalker itself. "I'm not sure exactly what the policy should be on those ROMs," Baker explains. "They're not my intellectual property, nor am I the one who dumped them, so I don't feel comfortable distributing the ROM images myself. Ideally the community would come together and see if they could make their way into the public domain."

A full write-up of the project, including schematic, can be found on Baker's website; the source code is available on GitHub under an unspecified license.

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