Olin Robotic Sailing Team

Finishing the PCB design is taking a lot longer than anticipated; we wanted to have it fully designed before Thanksgiving break, but we are still chugging along. Much of the delay was from honing down on the exact parts we were going to use to create the appropriate footprints on the PCB. Once we had our schematic created, we needed to associate the different components with patters that would define how the components would be attached to the board (e.g. holes of appropriate sizes and positions for through-hole soldering). The last step for finishing the PCB design is to lay out the traces for the board. The traces are lines of conductive material that connects the different components electrically. We should have the board done in the next week and ready to be ordered! The PCB will be smaller than the sbRIO, so our new waterproof housing can be much smaller than the old one.

Wanting to improve from last year, we’ve been researching other wire connection methods. Between asking around and searching the internet, we’ve found lots of new connectors we want to try. We ordered a sample of a wide variety of different wire-to-wire and wire-to-board connectors. We found some very good wire-to-board connectors from a company called Wago. They are great because they have a strong mechanical connection and require no soldering: switching out wires will be virtually effortless. We also found some tiny fuse holders from Littelfuse that connect directly to the PCB and perfectly match our needed range of values. We looked into some higher-grade through-housing connectors, but we didn’t find anything good enough within our price range, and ultimately decided that we would pass the wires straight through the walls and glue them in instead. This will make one less place for failure. However, if for any reason we need to redo the wire connections, it would be a very difficult and extensive task. For connectors outside the housing, we’re are pretty big fans of the MX150L series of waterproof connectors. We’ve found them to be much easier to use than other waterproof connector without a proper (and expensive) crimping tool.

Our test connector of the MX150L series.

One of the electrical teams goals for the semester is to turn our wiring inside the electronics housing into a printed circuit board (PCB). To do this, you need* EDA (electronics design automation) software. There are a number of free options out there, but there is a big trade off between easy to use and full featured. ExpressPCB, for example, is easy to learn, but you can only use it to order PCB’s from their company, and it lacks some really useful features. EAGLE, which has a free version for non-commercial projects, falls at the other end of the spectrum: it can do pretty much anything you could want, but from previous experience, we’re convinced it was invented before the idea of usability. Because we wanted to get this PCB done in under a month, it was important that the EDA software have a forgiving difficulty curve.

DipTrace is the Goldilocks of EDA software in the hobbyist/low volume realm. It can do pretty much anything EAGLE can, but it also has nice tutorials, and an intuitive user interface. The free version is limited to two layer boards, but DipTrace was kind enough to sponsor our efforts by giving us a full version of the program.

They have quite the slick logo too.

We’ve finished the schematic (in DipTrace) and are just starting to design the board itself, but so far we’ve been extremely happy with DiptTrace. We’ve been able to teach a group of new members how to use it in under 3 weeks, and it’s done everything we need it to so far. We’ve just finalized the schematic, so hopefully within the next two weeks or so, we should be able to show you some awesome PCB designs.

*Ok, you don’t need it, but it will save you a lot of time.