In writing up a tutorial I've been meaning to write for months, I remembered my frustration with the terminology surrounding, and sources for, connectors commonly used in DIY electronics. I know I'm not the only one who doesn't find existing stores of knowledge intuitive because I recently helped a friend of mine source female headers for a project — I know what I'm doing, and it took me a minute to find the relevent part on Jameco's site! Online vendors, particularly sites like Jameco and Digikey tend to be targeted at engineers who already know exactly what they're looking for. If you don't know the right search terms, finding the right part can be a bear. Since I made my start in electronics a few years ago, Octopart has made finding parts much easier, but you still have to know what you're looking for! In hopes of helping people who're building their first homebrew boards know what to look for, I've tried to compile a bit of what I've picked up. I'm entirely self-taught so it may or may not be accurate, but I'm hoping it helps make the learning curve a bit less steep.
Most electronics you're likely to build/interface with as a hobbyist use 0.100"-spaced pins. There are other, more finely-pitched connection options out there, but this is the bread-and-butter of low-voltage homebrew electronics. This is the spacing common to most solderless breadboards and DIP-package ICs, too.
Headers solder to PCBs and provide connectors that are easily connected and disconnected. They come in many varieties. Here, I discuss those which I've used, or which are commonly used in DIY electronics. There are, of course, a whole world of interconnection options, particularly if you deal with finer-than-0.100" pitch parts.
Searching for "0.100" male headers" yields a dizzying array of parts — 25,919 items in the "Rectangular - Headers, Male Pin" category at DigiKey; 64 in "Interconnects:Rectangular Connectors:.100" (2.54mm) Series" at Jameco; 3,458 in "Interconnects >> Rectangular Connectors" at Mouser Electronics. An Octopart search yields 46,300 results. Thankfully, most of these are variations on the same basic design and by understanding a few of the keywords these stores use to filter those results, you can find what you're actually looking for relatively quickly.
Unshrouded Male Headers
I'll start with the basics — unshrouded male headers are the duct-tape of interconnects. If you've ever assembled anything electronic with more than one board, you've seen a few of these. The image at right pictures "double-row male header;" single-row is also available. I find male headers handy (and versatile) because you can easily snip them to whatever length you with your diagonal shears -- I tend to buy 30x2 header and snip it into 5x2 and 3x2 for interconnects and AVRISP headers, respectively. 
You can use them to break out pins that need jumpers (see the Arduino board's external/USB power selector, for instance), and single-row male header is the perfect size to connect to most solderless breadboards — the Arduino Barebones Board can be built with the digital I/O header and VCC/GND header on the bottom of the board to exploit this to great utility, and LadyAda's Boarduino kits are built this way by default.
To purchase a header that looks like this on Jameco, Digikey, Mouser, or similar sites, you'll want to make sure you select "unshrouded" headers that mount with "through-hole" connectors. As with everything I'm discussing in this article you'll want 0.100" pitch.
Shrouded Male HeadersI'm covering these seperately from male headers because they're a much less flexible, but occasionally useful animal. These parts have the same pin configurations as their unshrouded counterparts, but have a plastic border surrounding the pins. The shell both protects the pins from damage and can be "keyed" with a small slot so that polarized sockets can only fit in one orientation. These can't easily be snipped to size and don't work well with jumpers. On the other hand, the keyed shroud means they're great for idiot-proofing connections, even (or maybe especially!) when the only idiot you're proofing against is yourself. You can even find variants with plastic latches for interconnects in vibration-prone environments.
Again, for typical use, you're looking at shrouded, through-hole mount, 0.100" pitch and spacing parts. There are many alternatives in terms of complexity/cost for shrouds, so make sure to check the datasheet!
I don't have any polarized headers on-hand to photograph; imagine, however, something akin to a shrouded header, but with only one long side of the connector shrouded. Polarized headers tend to have only one row of pins.
The Arduino introduced me to the very nifty idea of using female headers on PCBs, rather than male. Female headers are similar to the sockets that connect to male headers, but with through-hole pins rather than cable connections. If you're prototyping on a solderless breadboard, you can connect hookup wire directly between female headers and the holes on the breadboard. This is far handier for prototyping than trying to use various combinations of female-to-female cables and hook-up wire. Female headers also enable you to build "shield" boards with matching male headers that attach directly to your board, without interconnecting cables. Many Arduino accessories are designed in this way, and that's how the BlueSMiRF is connected to the Arduino in the NG/Diecimila-based wireless smart objects we build at AME.
Sockets connect to cables and attach to headers. They're typically female -- I may be mixing terminology here, actually, but this works for me. If there's a more appropriate generic term, please let me know!
Insulation-Displacement Connector Sockets & Ribbon Cable These connectors are commonly known as "IDC sockets." They consist of a two-part body that crimps down onto a ribbon cable, cutting (displacing, if you will) the insulation and making electrical contact. IDC connections are apparently considered to be of lower-quality than individually-crimped connections, but for speed and ease-of-use, it's hard to beat the concept. The IDC sockets Futurlec sells are keyed, which means they have a small plastic protrusion on one of the long sides such that they can only be attached to keyed, shrouded headers in one orientation. If you search for these on Digikey or Jameco, you'll have a pile of options — you probably want 0.100" spacing.
Octopart suggests a variety of suppliers, but I've purchased my connectors and ribbon cable from Futurlec — for instance, 10-pin female IDC connectors $0.25 ea, Futurelec PN:IDCC10; 10-conductor ribbon cable, $0.40 per meter, Futurelec PN:GRCABLE10. The datasheets for the headers will discuss the gauge/pitch ribbon cable that each requires.
Polarized Headers and SocketsPolarized headers have a small plastic tab on one side of the row of pins, unlike the shrouded headers discussed above. I don't tend to work with these, much, but I can see situations in which they'd be useful -- again, they're potentially useful in the pursuit of idiot-proofing your builds.
"Lab Cables"I'm honestly not sure what the "correct" term for these cables are. Anyone want to leave a comment? Unlike IDC sockets, which crimp onto a ribbon cable, these sockets connect to hookup wire -- each wire gets a crimp-on pin that is inserted into the socket body. They are sold in two parts by vendors like Futurlec -- "connector for male header" and "pins" To build a cable, you insert the pin and a stripped hookup wire into the connector body, which crimps them together. Pictured here, a two-conductor cable, but these connectors are available in most of the same sizes as the IDC sockets discussed above. They're handy to keep around for making quick connections on or between boards, but in most cases I find the IDC connectors more useful.
I found additional information on connectors at this site on pinball-machine repair.
This is only a rough first stab at trying to gather some knowledge regarding cables and connector sources for homebrew/DIY. I'm sure there are errors and ommissions here -- please comment if you have anything to add or see anything that's blatantly inaccurate.
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Reply #21 on : Fri February 12, 2010, 02:26:39