Personal digital assistants like the Palm Pilot, Handspring Visor, and Compaq/HP iPAQ range of devices were available before cellphones. The Psion Organiser, a relatively simple PDA that essentially had the same functions as a calculator watch, was another option before them.
One of those vintage organizers could be available on eBay, but YouTuber Volos Projects made his own using an Arduino Nano, a specially designed printed circuit board, and a small OLED display.
By the standards of contemporary computers, the Arduino Pocket Computer isn't exactly robust. The phone book, calendar, stopwatch, calculator, and support for a few simple games are all there, though, much as on a digital organizer from the 1980s or the first decade of the 1990s.
Expecting an Arduino Nano-powered portable computer to be able to perform much more would likely be unreasonable. A 16 MHz ATmega328 microprocessor, 32 KB of flash memory, and 2 KB of SRAM are found on the compact board.
%20old%20PDA..jpg "The functionality of this homemade Arduino pocket computer is similar to that of a (very) old PDA.")
The Arduino Pocket Computer might not be very useful (the tiny display is barely large enough to display games or calendar appointments, and the exposed components would likely snag in your pocket if you tried to carry this thing with you). But if you'd want to attempt constructing your own, it's a fairly spectacular DIY project. In the YouTube video's description, Volos has provided ordering links for printed circuit boards, and the GitHub website hosts the source code for the device's operating system.
Volos made all the files necessary for making your own Arduino Nano small PC available on his GitHub website.
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