It may seem counterintuitive, but the elimination of a digital interface in this device is actually better in addition to being cheaper.
The mirrors are actuated by electromagnetic coils - just like a speaker cone. To make it work, you need to feed an analog waveform to those coils. You could stick a microcontroller in the printer, feed it a digital file over USB, let it extract the data, send it along to a DAC, amplify it, and then pass the waveform to the coils. Or you could cut out several middlemen and just use the DAC and amplifier in your PC’s sound card and send the waveform directly over an audio cable. Even a cheap built-in soundcard DAC is going to be better than what you’d get from a low-end microcontroller, so this really is the best method.
