Tvornica Računskih Strojeva TRS612

I found this calculator in the ewaste bin at the Ljutomer city dump. OK, so what makes it interesting?

The first electronic desktop calculators were developed in the mid to late sixties, and while the very first models still used vacuum tube and discrete component technology, the market only really took off when MOS LSI chips were developed.

The first MOS LSI calculator chips were developed by GM-e, a spinoff of Fairchild. While successful, the process effectively bankrupted the company which was sold off. The brains trust of this process went on to start Electronic Arrays (EA).

Electronic Arrays announced a practical 6-chip calculator chipset (called S-100) in 1970, and published enough information that anyone including hobbyists could build their own calculators.

A small company called Micro Instrumentation and Telemetry Systems bought a variation of this chipset and developed a kit (article in Popular Electronics, November 1971) for anyone to build their own four-function calculator.

Of course MITS went on to develop the Altair 8800 which started this whole microcomputer thing.

EA developed many more calculator chipsets. Which brings us back to this calculator.

Tvornica = factory, računskih = computer, strojeva = machinery.

The PCB is marked "TRS 612.S." which matches "Tvornica Računskih Strojeva" and the 612 on the sticker on the back so I'm guessing that's the model number. The chips are EA7251 and EA7050 (display driver). The 3 x 9665 devices are buffers to the printer mechanism.

Built in 1978 or 1979, looking at the date codes. The factory was 30 years old then.

2023: Peek & Poke in Rijeka has one too, including the printer bits that fell off when they dumped mine -- but it also has the badge (I'm guessing -- the round area with two holes and dried glue) missing.