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There are literally thousands of different types of connectors when I'm searching on a distributor such as element14, and I'm not sure what are the "standard" ways of connecting boards together.

Currently, when I need to connect two different boards together, I will use a 2.54mm spaced pin header, and some ribbon jumper wires. While this is fine for prototyping, I want a more standard solution to connecting modules together (such as USB, D-Sub, HDMI connectors, etc).

Digital Communications

The protocols I normally use a I2C and SPI, so Vcc, GND, and the bus wires (SDA, SCL, MOSI, etc). For these protocols, are there any standard physical connectors which I should use when I want to connect boards together? e.g. RJ45 or something? I've always associated RJ45 with telephone comms, so not sure if there are more appropriate standard connectors.

Analaogue Communications

For example, if I want to drive a motor or fan, what type of socket should I use on my board? On computer fans, hard drivers, toys, etc. I have seen them use Molex or some tiny white connector. Is this a standard way of connecting analogue input/outputs? AFAIK Molex is a brand of connectors, but nowadays is it just a name for the type/shape of connector?

Protocol-less digital communications

For example, push button switches, and LED lights, etc. How should I connect these between boards?

Finally, in my latest project I need to connect my around 20 different connections (these include both vcc/gnd lines, analogue inputs, switch inputs, as well as an I2C line, and some multiplexer line select lines,) between two boards. Should I have different connectors for each of these, or is there one standard connector I can use for all the pins?

The distance of communication I'm talking about is 1 - 2 meters at most, however any information regarding longer range communication is also appreciated.

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closed as too broad by Chris Stratton, Bimpelrekkie, crasic, duskwuff, pipe Aug 4 at 15:53

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ For I2C and SPI, there is the Digilentinc.com PMOD standard... digilentinc.com/Pmods/… Among many other standards... \$\endgroup\$ – MarkU Oct 16 '14 at 3:06
  • \$\begingroup\$ I2C and SPI protocols don't really have a single, unified, industry-standard connector (unlike USB and HDMI which do standardize both the connector and the protocol.) So it depends on your system's requirements. Panel mount? High voltage? Automotive / Industrial / Wet / Outdoor use or other harsh environment? \$\endgroup\$ – MarkU Oct 16 '14 at 3:10
  • \$\begingroup\$ It could be as easy as standard headers, just like arduino-like boards do. As @MarkU mentions, voltage comes into play, so does current. Ribbon cable and male/female headers could do the trick, and has for many years...if they fit the specs of voltage and current. A 10x2 header would take care of your 20 pins at a standard of .1 inch \$\endgroup\$ – Enemy Of the State Machine Oct 16 '14 at 3:32
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Back in the day when I was doing this type of thing, I used to use the D-style connectors a lot for standard digital logic signals. They were cheap, came with pigtails already, and were a lot more durable than standard headers.

That said, there's not really a standard way to do it, because a lot depends on the electrical, environmental and mechanical needs. High power or low power? Do you see connecting and disconnecting it a lot? Does it need to be mechanically strong or can it be fairly flimsy because there isn't a lot of vibration or movement in the chassis? How many signals need to cross? How high speed are the signals...will they need a ground plane through the middle of the connector, or match a specific impedance?

Examples off the top of my head: The edge connectors that PCIE cards use (like a graphics card in your PC) are cheap, but aren't really made to connect and disconnect a ton of times, so probably not good to use in a lab environment. The molex connectors are usually used for power connections because they can carry a ton of current, so they would probably be good in other high-current situations like driving motors. Are you fairly space constrained? There are a bunch of teeny, tiny connectors that cost a bundle.

The best is when I was working for a defense contractor and we were getting a bunch of Hellfire missiles back from the first Gulf War in the 90's. A bunch of them came back because the connectors that were supposed to connect the missile to the helicopter were getting a ton of sand in them and failing to make contact. And how were they tested? The ground crew had to put each missile on the helicopter rail and slam it back HARD to see if that particular missile was going to lock into place and make contact through the connector or if it went into the crap pile to try to clean out later and try again.

Anyway...there are no real standards. Just figure out what works best for your needs. Good luck!!

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For board to board digital connection within the same enclosure, whenever possible I use ribbon cable with IDC connectors. That is fairly standard. For higher currents, I'd use a molex MTA connector with crimp connectors. I don't believe I've ever had to move a low-level analog signal between boards, so no idea what I'd do there. Shielded cable, but I don't know what connector I would use. Perhaps a mini SMA; I have an instrument that uses an LVDT and the connector to the LVDT signal conditioner uses SMA connectors. Ribbon cable is pretty standard for digital signals and can be purchased premade off the shelf.

Going outside the enclosure, well, things get complicated. My preference is always some form of circular connector because it's easier to drill/punch a couple of round holes than mill a rectangle. What I choose really depends on how many signals are needed.

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When it comes to consumer products, I found that a nice way to get some ideas is to simply disassemble existing products and see what kind of connectors are used. For at least board-to-board low frequency communication and some power transfer, I've found that FPC/FFC (flat flex) connectors are fairly popular due to the very small and thin form factor. The cables are off-the-shelf, with a lot of options on length, pitch and number of channels, and IMHO are very easy to assemble and disassemble.

Furthermore, it is possible to directly plug custom "flexible boards" into these connectors without a cable at all by building the cable directly into the flexible board, as regular off-the-shelf flat flex cables are essentially the same thing as such boards, though this is definitely not as popular as simply using an off-the-shelf cable.

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