TRS-80 Model 100 Gets Arduino Heart Transplant

When [Stephen Cass] observed himself with a damaged Tandy TRS-80 Design 100 portable computer system, the easiest answer was to purchase one more broken just one and make a single performing computer from two non-doing the job desktops. However, this still left him with a problem — what to do with the (now even a lot more) broken a single remaining more than?

Liquid crystal display layout is strange by modern conventional, but optimized for quickly updates

Naturally, he did what a great deal of us would do and applied modern-day components to interface with the initial components that nonetheless work. In this situation it meant replacing the motherboard with an Arduino Mega 2560.

Luckily for us, the Model 100 has a sizeable fanbase and there is a great deal of useful information available online, which include the in-depth assistance manual, that assisted [Stephen] to have an understanding of how to generate the unusual screen.  The Liquid crystal display has a resolution of 240×64 pixels, which are broken down into eight zones of 50×32 pixels, and two zones of 40×42 pixels.  Just about every zone is then further divided into 4 banking companies, eight pixels tall, so that every column of 8 pixels corresponds to a one byte.

Each a single of the 10 zones is controlled by an individual Hd44102 driver IC, linked to a 30-bit large bus for picking out the accurate chip, lender and column.

With the Arduino handling the details, the previous Liquid crystal display however essential a -5 V source for distinction and an RC filter to smooth out the PWM sign [Stephen] is employing to change the viewing angle.

With the new interface, [Stephen] is capable to obtain all of the pixels on the unique screen, and to use fashionable graphics libraries these kinds of as displayio. With the show issue solved, he intends to use a independent Teensy 4.1 to connect with the keyboard matrix and give a VT100 terminal interface.

Schematic of the Hd44102 driver circuit

Upcycling aged, broken components can be a whole lot of enjoyment and is usually instructional.  Understanding why certain design and style conclusions have been created at a time when the engineering trade-offs ended up distinctive can lead to insights that are specifically related to modern styles when methods get tight. In this situation, the quirky Lcd drivers had been a response to generating the display screen of textual content as efficient as doable, so as not to overburden the processor.

The TRS-80 desktops are ripe for hacking, with their “built-for-service” layouts, and we’ve showcased a couple in the past.  Some have changed the motherboard with a little something newer, like [Stephen], whilst other folks have also replaced the display screen, or related them to the cellphone network.

Have you observed new ways to get aged hardware operating? Convey to us in the opinions underneath or ship us a information on the Hackaday ideas line.

Thanks to [nb0x0308] for the suggestion!

By analia

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