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I am designing a prototype for a unit that may go into production (not for profit organization). For some of the parts, geometry will be important. I need a power jack, a two wire fan connector, a switch, and a 10K potentiometer. Obviously, I want to design the unit with the particular part geometries in mind and I want to ensure that any parts I use will remain available, or that equivalent parts from a different manufacturer will. There are standards on transistor packages, etc. Is there any standard for, say, potentiometers? Where can I browse these standards and pick a geometry that suits my application?

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  • \$\begingroup\$ mandatory xkcd \$\endgroup\$ – Nick Alexeev May 10 '14 at 3:49
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    \$\begingroup\$ I'm with Nick on this one; standards are great, but there are lots of them, and sometimes they don't agree on things. There are a few tricks you can use to make your board work with multiple different geometries, though, in case you can't get your normal part. Here's a guide I like. \$\endgroup\$ – Sean Boddy May 10 '14 at 4:49
  • \$\begingroup\$ TL;DR Nick's link - It's not that there aren't standards, the issue is every manufacturer has their own standard. We have too many of them. \$\endgroup\$ – Connor Wolf May 10 '14 at 5:59
  • \$\begingroup\$ If you purchase parts from reputable manufacturers, via well-known distributors (like Digikey, Farnell/Newark, Mouser) those parts are likely to be available much longer than parts from fly-by-night eBay vendors. \$\endgroup\$ – Peter Bennett May 10 '14 at 6:33
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Many major electronics suppliers (Mouser, Digikey) have parametric searches, so you can specify, for example, what transistor package you're looking for, or what potentiometer shaft diameter or mounting type you want. If you're looking for the most flexibility (swapping/upgrading/adjusting parts as needed) I'd suggest the following;

  • Choosing a specific transistor package and pinout, or designing your PCB for easily accommodating variations.
  • The power jack depends on what you need to supply, really. If you need DC then there are numerous designs, I typically use a 2.1mm jack like this. But by all means, let us know what your specific needs are.
  • Virtually all potentiometers I use have 1/4" shafts, requiring a 3/8" mounting hole. The case size is often labeled (somewhat confusingly) 16mm. 24mm is also common.
  • As for fans, I suggest choosing a specific voltage (5V and 12V are common) and size (there are a few standard computer sizes). There are a few different types of connectors, so what you could do is cut them off and use spring or screw terminals on the PCB to connect them to your circuit.

Of course, I'm making a few assumptions (you'll be mounting things on some sort of chassis or panel, and by potentiometer you don't mean a trimmer) but again, feel free to specify your needs/intentions and we'll be happy to clarify. I realize I haven't exactly specified standards per se, but my aim was to show you some regularly available options.

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The military is your friend. For every transistor package, potentiometer, and power connector there is a corresponding MIL-STD (visit Everyspec.com or search for [$Product_Type specification site:.mil]). Nearly all commercial-grade electronic components are exactly the same as their military-grade ("mil-spec") counterparts, except mil-spec parts are supposedly more durable and are guaranteed by the manufacturer to work in extreme temperature and other harsh environmental conditions.

Government specs are fascinating stuff, incredibly detailed and comprehensive. Not only are there specs for electronic components such as potentiometers, but also for common consumer items (that the government sometimes purchases) from peanut butter to ladders to toilet paper.

What this means for your design selections is that most commercially available electronic components are derived from mil-spec products and they will probably have the same "geometry" in the future as they do today.

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