Connector: Basics
There's a huge number of connectors out there; quite easily thousands of different designs made by hundreds of manufacturers. What I want to do here is start with the basic parts of a connector and then dive into specific types of connectors that are good to be familiar with.
Let's call it the taxonomy of connectors, or at least a weak start of one. To give you a rough idea of how enormous the connector field is, here's just the top-level categories (and counts) for Digikey:
As you can see, they catalog over 2.4M circular connectors alone. In other parts of this section, we'll look at the kinds that I think are most useful, and a few just super interesting ones.
Housing or Shell
The housing is the thing that holds the entire connector. In many ways it basically defined what kind of connector you're working with. They housings break down into two major groups: rectangular and circular. I'd estimate that 60-70% of all the connectors fall into the rectangular category.
In the schematic to the right, you can see a JST XH connector. There's two pieces to the overall connector housing, which will talk about later under gender. The housing has a few things that make it distinctive above and beyond the basic size. On the front, you can see keys that help ensure that 1) the connectors mate together correctly, and 2) you don't reverse the polarity of the connector. Not every connector has keying to prevent polarity reversal, but you should use them whenever you can as they reduce the likelihood of damage to a circuit.
About JST Connectors
You'll often hear JST used as a generic connector term, and many of the designs are made by hundreds of companies. However, the original JST connectors refer to Japan Solderless Terminal, the company. They still make the best versions of their connectors.
The housing can be one of many formulations of plastic or metal in many higher-end connectors.
Contacts
Contacts are the part connector where all the business of moving electricity happens. They are the metal parts which touch each other, forming an connection. This can also be where problems occur: the contacts can become oxidizer, or even they can accumulate dirt. Finally, due to the nature of the material of the contact, the spring that is used ot hold them together may reduce with time, and you will get weaker and weaker connections exhibiting problems such as intermittent connections, or even shorts.
Many times, the connectors are made of phosphor bronze and plated with tin, silver, or gold. You will also find things like beryllium copper. Sadly, some very cheap (and low reliability) connectors might skimp and use steel or aluminum. Neither of those are desirable in most circumstances.
Durability
When we talk about the durability of the connector, we are mostly talking about the contacts. The housing is generally, baring any damage, going to last approximately forever. When we talk about the durability of the contact, we are typically talking about insertion (mating) cycles. This is one insertion and removal of the connector. For high-durability connectors, this number will be specified, but often it is difficult information to get. If you don't see it, you should assume a lifetime of (approximately) dozens to small number of hundreds insertion cycles. Connectors designed for constant use, like USB-C, have much higher numbers. For example, USB-C's standard requires a minimum of 10,000 insertion cycles on a connector, and most can sustain many more.
Gender
Topic
Yeah, I know. This is just the way the industry has historically been and is what you'll see on nearly every datasheet you find. I'll try to use a few different terms that are common. If you want to dive into more detail, Wikipedia has a deeper article exploring all the terminology.
In most circumstances, connectors come in two parts. A part that has exposed pins, and a part that doesn't. The part that has exposed pins is typically called "male", but you'll also see "plug" and "pin". The part that doesn't have exposed pins is typically called "female", but you'll also see "receptacle", "jack", and "socket".
For threaded connectors (see locking below), the gender refers also to the standard polarity configuration of the threads. A male/plug connector will have threading on the inside of the housing, whereas a female/jack will have the threading on the outside of the housing. If this is flipped, they are called reverse polarity connectors.
Locking/Non-Locking
Some connector designs have locking mechanisms designed into them. These are intended to ensure that the connector doesn't accidentally come free and, depending on the design, they may be able to endure quite a lot of force before releasing or breaking.
The first kind of connector is one that uses a tab or snap piece to hold it in place. A great example of this is the Ethernet connector shown, where a small plastic tab is used to hold the plug into the jack.
The tab can come in a lot of different formats, but this is the weakest of all the connection locking mechanisms.
The BNC connector is a great example of a bayonet style connector. With these styles of connectors, you push the connector, then twist a partial rotation to lock the connector in place.
The push-pull connector insert into one another with multiple small tabs inside the housing to hold it together. The differences from the "snap/tab" connector are that 1) there are multiple tabs (3 typically) that are required to mate, and 2) the push/pull means there's a ring or other mechanism to release that has to be pulled back.
Screw connectors are the most secure, and come in a ton of different forms, metal and plastic. They require multiple rotations of the outer housing to lock the connector in place, but once secured, they are able to endure quite a lot of force on them.
Mount Type
This can be confusing, as the term mount is used to refer to several things: what the connector is mounted to (PCB, panel, cable), the angle of the connector relative to what it's mounted to (right-angle, straight, or other) mount, free-hanging, board mount), what the angle of the connector is relative to its attachment (straight or right-angle), or even how the individual conductors are attached (through hole, SMD, solder tab, or solder cup).
Comments or Questions?
If you have any comments, questions, or topics you'd like to see covered, please feel free to either reach out to me on Mastodon (link below) or open an issue on Github.