Building an embedded device for sailboat racing: a digression on suppliers…

This is the third post in a series about building an embedded electronic device to assist in sailboat racing.

Marine electronics project — table of contents

  1. Project background
  2. The platform
  3. A digression on suppliers…
  4. The software
  5. Power and packaging
  6. Fabrication and assembly
  7. Mounting and installation (take one)
  8. Installation (take two) — Success!

This post covers some details about the shopping needed to identify and acquire elements described in post #2, “the platform,” as well as the numerous other smaller components that went into the complete assembly. This was a lot less straightforward than just shopping on Amazon, so hopefully this offers some useful tips to you for any future electronics hunts.

The Newhaven display wasn’t for sale on Adafruit; I had to go to DigiKey for this one. DigiKey is basically The Everything Store but for electronic components. For everything from wires and cables, to integrated circuits from the generic to the sometimes absurdly-specific purposes, to fully-integrated displays and beyond… if it transfers or uses electrons, they’ve probably got it in stock or available on back order. The interface is hard to use; there are categories to browse but in practice getting started requires knowing what keyword to search for. But once you’ve run a search, they have an impressive faceted filter system to drill down a list to a few specific options. They also treat professional or power-users well, with links to CAD drawings and reference manuals, and price discounts for purchasing in bulk. Unfortunately, that bulk purchase point means that for amateurs like me who only ever need 1 or 2 of something at a time, I was paying full freight.

A competitor named Mouser has a similarly expansive catalog and very similar site user interface. Their prices are similar but do sometimes mismatch. Sometimes if DigiKey is out of stock on a part, it’s worth checking Mouser or vice versa. And for expensive components, it’s worth double checking both sites to see if they’re cheaper on one or the other.

Adafruit, on the other hand, is a very amateur-oriented site. If you’re building an Arduino or Pi-based project, you should probably start here for parts selection. The product descriptions are aimed at enthusiasts, and they have video demos of some of their products. The site is clean and modern looking, whereas DigiKey and Mouser’s web interfaces are somewhere between “intimidating” and “dated and ugly.” Adafruit is also focused around Arduino- and Raspberry Pi-based products, with a variety of displays, cables, and accessories aimed at complementing these base platforms. They also have a lot of “getting started” products available like soldering irons and stations, insulating mats, wire spools, etc.

Unfortunately, they’re also very hard to browse. If you don’t have the right keyword in mind to get started with a search, it’s hard to use their category browsing, since the many products in a category basically show up in a random order with no relevance-based sorting. They also lack the facet-based filtering that make DigiKey and Mouser powerful. Finally, they often hide from you the precise manufacturer’s part number (MPN) and don’t always provide datasheets. If you can identify the exact MPN for a component sold by Adafruit, it might be cheaper on DigiKey (Adafruit charges a markup for the convenience of having a useful collection of hobbyist parts in one place) — and you can also get the datasheet from DigiKey to verify that the part will perform to the level you need it to.

Sometimes later on in this project’s life, while searching through Adafruit for a particular component, I would stumble across some other thoughtful accessory that would have turned something else I’d already designed and built myself to solve a given problem into a much more plug-and-play experience.

In a few key parts of building this, I was assisted by my friend Matt, who’s a lab automation / mechatronics engineer. In his estimation, having a thorough knowledge of the supplier catalogs and knowing what to search for (and how to search for it) is a significant part of what makes an effective hardware engineer. Being familiar with the Adafruit catalog and what parts you can buy can help you put together homebrew electronics projects with a lot more ease.

While you can get basic screws, nuts, etc. from your local hardware store, for mechanical components (screws in odd sizes, other specialty fasteners, O-rings, a very thin sheet of silicone, etc.), the ultimate catalog is McMaster-Carr.

I also bought a DC-DC regulator from Pololu, who have a more robotics-centric catalog than the other electronics suppliers above, but also have a ton of basic IC and wiring components. Their components are also available from DigiKey or Mouser, as well as resellers on Amazon, but you can also buy directly from them, which may be cheaper or faster, depending on the part.

Finally, speaking of Amazon, I’d be remiss if I didn’t mention a few words about them. There are a lot of small components (especially things like USB connectors, CF cards, etc.) available on everyone’s favorite online retail store. While they’re not as good at things like offering access to datasheets on sales pages for components, and aren’t effective for bulk orders (if you plan to scale up a BOM later), a major advantage of Amazon is fast, free shipping for prime customers. The ability to pay for “just the part” and get it in two days is amazing.

All the other vendors I mentioned above will take 3 days to a week to ship you something, and they tend to have pricey shipping charges. If something is rated at 1 lb shipping weight (which is often an overestimate), Adafruit will charge $12.95+ for shipping. Because of this, I would also tend to “stock up” on other things that would or could be useful because I couldn’t swallow $13 for shipping a $4 part on its own; I might as well get my money’s worth, right? (And for some reason, adding several more parts usually didn’t increase the shipping weight at all! I don’t understand how that calculation works — since for some orders they only assessed a $4 fee to ship a correctly-assessed 0.2 lb package weight.)

In any case, you can save a lot of money on shipping if you build up a more complete BOM and order as one complete shipment, or at least have a small number of big chunky orders. Also, if you think you’ll need two of something (or might break it) and the part doesn’t cost too much, consider doubling up preemptively. It’s frustrating to delay work by a week because you fry a $3 IC, and equally frustrating to pay $3 for the replacement IC and $5 for shipping… especially if you may do another project at some point in the future with several of the same components, buying more stock upfront might save you money in the long run, given how much of this project’s total budget would eventually be consumed by shipping costs.

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