IIRC, one of the 8-bit Atari magazines had an article describing a similar setup back in the mid/later 80s. Basically, put a photoresistor in a shroud (I used the cap from a Bic pen and some electrical tape), attach it to the dot matrix print head and wire it to the Atari joystick port's analog/paddle input. Place a bright light over the printer. Then the software told the printer to move the print head back and forth while it read the port value. The image quality was terrible but it was a fun project.