In the 90's I was on a research ship writing software that towed an instrument (SeaSoar) behind the ship that could be "flown" up and down through the water col

In the 90's I was on a research ship writing software that towed an instrument (SeaSoar) behind the ship that could be "flown" up and down through the water column. One of the challenges was to make it not go so deep when we came up on the continental shelf. Given the idle nature of a month or two at sea, I started looking at the bathymetric electrostatic chart printer we had, and realized it had some kind of 4 bit output that was basically the raster of each depth print scan. So what I recall is wiring up the 4 pins to the 4 inputs (Busy, Paper-Out, Select, Error) on the DB25 on some PC, and scanning those to read the current bathymetric trace. Then turn that into a visual depth display overlaid on the 640x480 VGA display of the SeaSoar's position. Eventually then, I was able to figure out where the bottom was and have it automatically do a "turn up" when it got within a certain range of the bottom. Bit of a knuckle biter the first time I had to trust it to not smash a quarter million $ instrument into the sea floor. These were fun hacks. You're at sea, no internet, no place for parts, just hacking together stuff and dealing in the moment.