@voxel@merveilles.town pretty much any TI or Casio scientific calc has hex inputs (they're alts on the number keys), they work off solar if the light is bright enough and switch to either a button battery or AAA if it's not. You can take the battery out on most of them and they will still work if the light is bright enough though, just not recommended because that was a MAJOR downside of fully passive ones, they'd be super dim and if you didn't have the window open or a lamp over it they'd often just die.