Posts in the “Hardware” Category

The TRS‑80 Telephone Interface

The TRS‑80 Telephone Interface was the first modem that Radio Shack sold for the TRS‑80 Model I. According to the product introduction in the November 1978 issue of the TRS‑80 Microcomputer News:

Data communications can materially expand your computing horizons. It means you can communicate with large “data base” computers, using your TRS‑80 as an intelligent peripheral.

There were two versions of the Telephone Interface: the $149.

The TRS‑80 System Carrying Case Set

The TRS‑80 System Carrying Case Set (catalog number 26-500), also known as the Model I Carrying Case Set, was Radio Shack’s solution for transporting a TRS‑80 Model I. It was introduced in late 1978 for a price of $69.95. Radio Shack increased the price to $75.00 on July 1, 1980 except for a brief sale price of $39.95 that ended December 31, 1980.Although the Model I wasn’t a portable computer (by any stretch of the imagination), people often needed to move a Model I to a new location.

The JFF Electronics Color Graphics Interface

The Color Graphics Interface from JFF Electronics was one of the first color add-ons for the TRS‑80 Model I. It cost $49.95 when it was introduced in early 1979 by JFF Electronics Ltd of Saskatoon, Canada. The Color Graphics Interface didn’t require a Radio Shack Expansion Interface but plugged directly into the Model I 40-pin expansion bus. It didn’t include an enclosure but was a bare circuit board. However, it did include a regulated power supply on the board.

The XRX Cassette Modification

The XRX was an official hardware modification from Radio Shack for the TRS‑80 Model I. It installed inside the Model I and made it easier to load programs from cassette using Level II BASIC. Radio Shack dealers would install the XRX for free on any unmodified Model I. (For owners with a modified Model I, the installation price could range from $30.00 to $50.00.) Model I’s built after the XRX was introduced included it as a standard feature.

The Photopoint Light Pen

The Photopoint was a popular light pen for the TRS‑80 Model I and Model III. It cost $19.95 and was sold by Micro Matrix of Pacifica, California. Although virtually unknown today, light pens were once considered the way of the future to select items on a computer screen. The Photopoint was much less expensive than competing products when it was introduced around 1980 (some of which cost hundreds of dollars) and provided a way to experiment with light pen technology.


Orchestra-90, also known as Orch-90, was a popular hardware sound add-on for the TRS‑80 Model III and Model 4, and later the Color Computer. It was created and sold by Software Affair of Sunnyvale (originally Santa Clara), California, along with Orchestra-85, the equivalent add-on for the TRS‑80 Model I. It became more popular when Radio Shack began selling a licensed version of Orchestra-90 in 1984.


Probably the biggest design mistake Radio Shack made with the TRS‑80 Model I was their decision to use solder-coated tin contacts (instead of silver or gold) on the Model I and Expansion Interface connectors. These solder-coated contacts tended to oxidize over time, leading to reliability problems and unexpected reboots. The usual solution was periodically to use a pink rubber eraser to remove the oxidation.

The Exatron MM+

The Exatron MM+, also known as the Exatron Memory Plus Expansion, was an alternative to the Radio Shack Expansion Interface for the TRS‑80 Model I. It was designed and sold by Exatron of Sunnyvale, California for use with their floppy disk storage alternative, the Exatron Stringy Floppy. Despite the fact that it was barely advertised and seems to have been only sold briefly in 1981, the Exatron MM+ remains one of the best remembered Expansion Interface alternatives.

The Model I Printer Interface Cable

One of the limitations of the cassette-based TRS‑80 Model I was that it had no printer port. There were many cassette programs designed to use a printer, such as Electric Pencil and Scripsit, but no simple way to add one. Only a few Radio Shack printers were designed to connect to a cassette-based Model I directly.

The usual approach to adding a printer was to buy a Radio Shack Expansion Interface.

The Microtek MT-32

By itself, the TRS‑80 Model I was capable of only limited expansion. In order to add memory beyond 16K and support floppy disk drives, Radio Shack sold an external device they called an Expansion Interface.

The Expansion Interface could expand memory to 48K, add a parallel printer port, and add a disk controller for connecting floppy disk drives. But an Expansion Interface with 32K of memory cost $597.00, almost $100 more than a 4K Model I.