Don Wilcher's Radio Shack Science Fair Microcomputer Trainer Gets a Raspberry Pi Pico Accessory
Standing in for a finger on the keyboard, this merging of worlds across time shows how even old devices can be brought back into service.
Don Wilcher has given a vintage "microcomputer trainer" a serious overhaul by connecting it to a Raspberry Pi Pico — a device orders of magnitude more powerful than the Texas Instruments TMS1100 microcontroller around which it was based.
"Long before the Heathkit 6800 microcomputer learning system, the Arduino UNO, or the Basic Stamp, there was Radio Shack's Science Fair Microcomputer Trainer kit," Wilcher writes in an article for All About Circuits, brought to our attention by Adafruit. "Introduced in 1985, this easy-to-program kit was intended to teach users how microcomputers worked."
The gadget was inspired by earlier electronics project kits, which placed common components on a cardboard layout with spring terminals allowing them to be connected in a variety of ways — often advertised, somewhat generously, on the packaging as offering 30, 50, or even 100 individual projects. The Radio Shack Science Fair Microcomputer Trainer took things further by capitalizing on then-nascent interest in computing, adding a Texas Instruments TMS1100 microcontroller to the layout and a simple keyboard through which it could be programmed.
Marketed as the first single-chip microcomputer, a device type that would later be known as a system-on-chip, the four-bit TMS1100 offered a single core, 2kB of read-only memory (ROM), and 512 bits — not bytes — of random-access memory (RAM). To this, Wilcher has something a little more modern: the Raspberry Pi Pico, whose RP2040 microcontroller offers two 32-bit Arm Cortex-M0+ cores running at 133MHz, 264kB of RAM, and which links to an off-chip 2MB flash ROM. In short: a supercomputer by comparison to TI's 1975 microcontroller.
In Wilcher's project, the Raspberry Pi Pico is first built into a standalone digital clock with a relay output. This output is then connected to the trainer, which is programmed to act as a seven-bit binary counter — triggered, of course, by the Raspberry Pi Pico, which is no longer a straightforward clock but rather a pulse source with adjustable contact speed. Each time the Raspberry Pi Pico sends a trigger, the trainer reads it as an increment operation for the A-register in the microcontroller.
"As this project illustrates," Wilcher concludes, "the vintage Science Fair microcomputer kit can easily be resurrected and enhanced using today’s embedded technology platforms and a few electronic circuit modules."
The full project write-up is available on All About Circuits.