Found this gem in a customer's garage. Any thoughts on what it could be? […] Late husband's build from about 40 years ago – 209Diamondhander.
As DZP points out, the owner may have built one of Don Lancaster's TV Typewriters from the 1973 Radio-Electronics magazine plans.
The project documentation is available in this PDF.
This is not a computer, not really a terminal either. Rather a simple character generator ("Build this TV Typewriter and display messages on your set's screen").
This construction project started out as a very low-cost computer terminal for home use, but as it went together, we became aware of the many possible noncomputer uses for such a device, particularly since it is priced right – Don Lancaster (1973).
A machine that puts letters and numbers on an ordinary unmodified TV set.
What can you do with such a thing?
According to the designer: "Obviously, it's a computer terminal for timesharing services, schools, and experimental use. It's a ham radio teletype terminal. Coupled to the right services, it can also display news, stock quotations, time, and weather. It's a communication aide for the deaf. It's a teaching machine, particularly good for helping preschoolers learn the alphabet and words. It also keeps them busy for hours as an educational toy."
Thomas, the guy behind the Chyrosran22 YouTube channel, sums up how keyboards changed during the last fifty years and takes a look at the explosion of innovations that have happened in the field over the last few years.