This does make it a bit more complex though, because the microcontroller, though simple, still needs a board and some kind of power supply, and a reasonably accurate DAC for controlling the galvanometers. The microcontroller would have to spend the time in between DAC timer interrupts to perform the "modem" function. Not too bad since for this project the DAC only needs a frequency of 8kHz or less, but still mildly challenging. You could just use an RS-232 or USB interface instead of trying to create a modem since that would be easier and perhaps more reliable.