Unlike most other electrical components, most connector manufacturers do not append any letter codes in the part numbers for connectors, rather they are just a long sequence of numbers. This can make part recognition very confusing (e.g. when you see an IC with “74” in it’s part name, you instantly think of digital logic). A standard way to indicate pin 1 on a connector PCB footprint is to make the copper pad surrounding the pin 1 hole to be a different shape than the rest (e.g. square, while all the others are round).


Term Description
Female See socket.
Genderless A connector that can be mated with it’s self (i.e. there is no seperate male/female or plug/receptacle parts).
Header Can either stand for a particular style of connector (see the Header section), or it can stand for a male gender connector.
Hermaphroditic See genderless.
Loaded On connectors with a large number of pins, this indicated how many of the pins come shipped with contacts. The contact pattern can also vary.
Male See plug.
Plug A connector which has rod-shaped part for plugging into socket. Also called a male connector, or header.
Receptacle See socket.
Socket A connector which has holes that accepts plug pins. Also called a female connector or receptacle.

Connector Manufacturers

Name Website Range Provide 3D Models Affordability (1 expensive, 10 cheap) Site Usability (1 bad, 10 good)
3M http://www.3m.com/ Card edge (inc. latching) Yes, but not always for all parts in a connector family. (Step, IGES, Parasolid) 3  
Harting http://www.harting.com Card edge Yes (Step) 5  
Hirose http://www.hirose.com/ High-end circular Yes, after providing your paid-for email address. (Step) 5  
Molex http://www.molex.com Card edge Yes (Step) 3 6
Samtec http://www.samtec.com Backplane, headers (various pitches, and both square-post and machined), rugged circular. Yes (Step). 7 8
TE Connectivity http://www.te.com Backplane ? 6  

Connector Materials

Material Strength
Polybutylene Terephthalate (PBT) ?

Tin vs. Gold Plating

Many connectors come to at least two plating options, either tin or gold. Gold is a more expensive option, but offers a lower initial contact resistance, lower corrosion over time, and lower mating force (which may or may not be a good thing).

There is the 50:50:50 rule (taken from www.connector.com) when it comes to deciding which plating to choose. The rule says that tin is the best choice if:

  • You have less than 50 contacts (due to the mating force getting too large)
  • The connector will experience 50 or less mating cycles
  • You can live with 50mOhms of contact resistance over time

Selecting gold tinned contacts can add a good US$0.50 or more to the price of the connnector.

Mixing the two plating metals is not recommended! The corrosion rate is greatly increased when two dissimilar metals come into contact with each other (this is due to the difference in the metal’s electrode potentials, which is +1.5V for gold, and only +0.15V for tin).

gold-and-tin-plated-contacts You can see the difference between the gold and tin plated header connectors. Image from http://www.fischerelektronik.de/en/latest-news/press-releases/releases/smd-high-precision-male-header-with-2point54mm-grid-spacing-horizontal-design/.


The term “Header” normally refers to a basic row of pins or sockets, with little or no additional features such as shrouds, locking ability, or keyed parts. The most common pitch for headers is 2.54mm (100mil). Headers are versatile, as they not vendor-specific, can be connected to by soldering, hooks/probes, or the opposite gender header (either a plug or jack), normally have a standardised pitch, can handle a decent amount of current (at least 1A for normal 2.54mm headers), and are cheap!

Headers are used frequently on electronic development kits. For example, the Arduino, RaspberryPi, and PSoC development kits all use headers for various things such as programming the microcontroller to providing a way to connect expansion boards.


Headers can have two different pin types, square post of machined post. Square-post headers have square pins, while machined post header have circular pins. The machined post headers are more expensive, but can take more current as there is more contact area between the male and female parts.

You can also get headers which are polarised, usually by both the male missing one pin, and the female part missing the associated hole. This prevents the common mistake of plugging in a header offset by 1 pin or completely the wrong way around. Note that careful choice of the missing pin is required to minimise the chance of an incorrect mating.

Typical Pin Numbering

Male headers (plugs) are normally numbered from left-to-right, when the connectors solder terminals (tail end) are facing south on the PCB, and the bits that do the connecting are facing north (all of this while looking down on the PCB). For female headers (jacks) to match, they are numbered from right-to-left. This is all better explained in the following image.

typical-numbering-order-for-header-connectors This image show the typical way in which headers are numbered, with males headers (plugs) being numbered left-to-right and female headers (jacks) being numbered from right-to-left.

Using Headers For Board-to-Board Connections

They are also a great, cheap way of connecting two or more PCB’s together, as shown in the following image. A disadvantage is that this method is not as mechanically strong as some more expensive custom board-to-board connection methods.

2-54mm-smd-right-angle-header-plug-and-jack-mosaic Header plugs and jacks (male and female parts) are a good way of connecting PCB's together.

Part Links

Samtec make some good priced, 2.54mm pitch square-post connectors.

D-Subminiature (D-sub) Connectors

These connectors were designed by ITT Canon in 1952. Large by today’s standards, at the time, these connectors where one of the smallest connectors available for a computer, hence the name “subminiature”. They are characterised by two or more rows of connections inside a “D” shape metal shell.

The DE-9 is a very popular 9-pin computer serial cable. It is also commonly (and incorrectly) called a DB-9 connector, presumably because of the name of larger DB-25 connector that it replaced.

The DE-15 connector is commonly used for VGA connections between computers and screens.

Mass Pinned Header’s

These are good for making many connections between PCB boards, while holding the boards parallel or perpendicular to each other.

Example: Harting 0903 296 6825 96pin DIN41612 Socket Element14 Code: 1096910

Board-To-Wire Connectors

One of the most common type of connectors, these do exactly what they say, get wires to boards and make them stay there. Connectors get rid of all the problems with soldering wires directly onto a PCB, which include fatigue/breaking issues, short-circuit woes, and the ease of disconnecting/re-connecting the wires.

Trying the find a good, cheap header on a electronic supplier’s website can be near-impossible. There are so many varieties, shapes, lead pitches, bad datasheets, and different manufacturer’s making nearly identical products. Also, to top it all of, you need to usually find more than one item to make a connector work (e.g. if you buy a header you must also find the matching receptacle and crimp pins). And most suppliers don’t do a good job and making the related parts obvious.

TE Connectivity’s 2.0mm HPI SMD Connectors – Good choice if you want a smallish SMD connector’s for anywhere from 2 to 12 wires. I like these because they are relatively cheap, have good documentation, and best of all, come with 3D step models for creating a 3D mock-up of the PCB. Their code is 1775469-x where x is the number of connections.

PCB Card Edge Connectors

This is a cheap and many-pin capable solution when you want to connect two PCB’s together. PCB card edge connector involve using the edge of one of the mating PCB’s as the connector, by etching/routing “fingers” on the PCB. The other mating part of the connector is designed to accept these fingers. Most card edge connectors are used when the PCB’s are at right-angles to each other, although you can get connectors designed for parallel and co-planar connections.

The fingers that are etched on the PCB are usually gold plated to make the contacts more reliable (the normal lead/tin coating oxidises too quickly). This is a special process that most PCB manufacturers will support, and does not add much to the cost of the PCB. The supported PCB thickness of most of these connectors is around 1.60mm (which is pretty standard). Also, it is recommended to add a small bevel to the inserted end of the PCB to facilitate mating. Again, most quality PCB manufacturers will support this.

Card-edge connectors are very susceptible to board warping and board thickness errors, so takes these into consideration when adding card-edge connectors to your PCB design.

edge-connector-gold-fingers-and-bevel Edge connector fingers which have been gold plated and the PCB bevelled. Image from http://www.eurocircuits.com/index.php/eurocircuits-printed-circuits-blog/gold-plating-for-edge-connectors.

The following image is of PCB card edge connectors on the Cavro XL-3000 syringe pump.

pcb-card-edge-connector-example-from-cavro-xl-3000 An example of a PCB card edge connector. This is a photo of the Cavro XL-3000 syringe pump.

You can get PCB card edge connectors which have latches, which lock in the daughter board which has special “hockey stick” pieces routed on the sides.

pcb-edge-connector-pci-hockey-stick-png Male pcb-card edge connectors can have "hockey-stick" latches as indicated (the female connector also has to support this).

This is a screenshot from a PCB design for the male part of a card-edge connector in Altium.

altium-card-edge-male-connector-on-pcb-png An Altium PCB design of a male card-edge connector. This is for the 20-pin connector in the Molex SPD08 series.

This is a female latching card-edge connector.

pcb-connector-with-latches-3m-spd08-png A 20-pin card-edge female connector from the Molex SPD08 series.

In some rare cases (e.g. the Sullins EBC Card-Edge connector series), aside from the socket, the connector manufacturer will also manufacture a plug which replicates PCB fingers, instead of you using the PCB for this purpose.


USB plug assemblies (non pre-assembled plugs) are hard to come by. However, they do exist. Here is a picture of a Molex Mini-USB Type-B plug assembly.

molex-mini-usb-type-b-plug-assembly-photo The Molex Mini Usb Type B plug assembly.


Jumpers are used to connect adjacent pins on a header together. They can also be called zero-Ohm links or zero-Ohm resistors. 

using-jumpers-to-connect-pin-headers-to-test-leads A clever way of using jumpers to connect test leads to header pins. Image from http://hackadaycom.files.wordpress.com/2013/06/dgcaicca.jpg.

The term zero Ohm resistor is usually reserved for a resistor package whose resistance is close to zero ohms. In recent years these have tended to be in small SMD packages such as the 0603 chip package. A problem with these zero Ohm resistors is that they usually have quite a high resistance compared to a similar sized track on the PCB. Manufacturers also make “true” zero links in these packages, designed to have a much smaller resistance. One such example is the Keystone 5110, an 0603 sized zero-ohm jumper.

3D model of the Keystone 0603 "true" zero-Ohm jumper. Image from http://www.keyelco.com/product.cfm/Zero-ohm-SMT-Jumpers/0603-Zero-ohm-SMT-Jumper/product_id/14038.

3D model of the Keystone 0603 “true” zero-Ohm jumper. Image from http://www.keyelco.com/product.cfm/Zero-ohm-SMT-Jumpers/0603-Zero-ohm-SMT-Jumper/product_id/14038.

Terminal Blocks

Terminal blocks are a great easy-to-use connection method for signal from mA right up to 10A+. They make it easy to connect (and re-arrange) wires, accept one of the largest ranges of wire sizes, and the standard screw type requires no crimp on the end of the wire. They are also great because they allow the cable itself to be fed through glands and other small orifices, as there is no mating connector permanently mounted onto the end of the cable.

There are different types of terminal blocks:

One piece These are your standard terminal blocks that are soldered onto PCBs.
Feed-through Rather than connecting to a PCB, these provide mechanical contacts on both sides of the terminal block, allowing wires to be connected together. Popular with mains (household) wiring.
Pluggable These are like on-piece, except that the PCB part and the wire part are plugged into each other, so that they can be seperated.
Barrier These provide electrical isolation.

You can see the push-in terminal blocks I used to connect up all the solenoids for the Luxcity Tonic project in the image below (the green things with numbered stickers and wires coming out of them).

arduino-relay-shields-and-relays The Arduino, the relay shields and the relays, set-up for testing.

However, because they do not enforce a specific wiring configuration, they are prone to wiring errors, especially if someone else than that who designed the circuit is wiring it up.

Common pitches for terminal blocks are:

Pitch Use
2.54mm (100mill) Imperial pitch used for small wires (16-30AWG). While this is a very common pitch for other connectors, the design of terminal blocks actually makes this result in very small connections, hence larger pitches are more popular.
3.5mm This is a metric pitch.
3.84mm (150mill) This is a common terminal block imperial pitch
5.08mm (200mill) This is a very common imperial pitch.

A word of caution: DO NOT completely tin the ends of wires that go in the terminal block. Under the pressure of the screw, solder will creep over time, and the connection will become loose, either falling out, or making a high resistance connection. It is acceptable to lightly tin the very ends of the wires to keep the individual strands from fraying, but nothing more.

A better way to fix this problem is to use wire ferrules. These are small hollow metal cylinder which just fit over the wire and then crimped onto it, before being inserted into the terminal block. It stops the wires from fraying, and gets rid of the solder creep problem.

wire-ferrules-used-in-terminal-block Wire ferrule are crimped onto wires before they are inserted into a terminal block, preventing fraying and solder creep.

Connection Type

Terminal blocks have many different connection types:

Connection Type Image Description
A terminal block with a screw-style connection method.

A terminal block with a screw-style connection method.

The most basic terminal block connection type. I don’t particularly like this connection style, especially when clamping bare wires (i.e. no wire ferrule), as the screw can pinch and break the individual wire strands, as well as the screw completely missing some/all of the wire strands if they ride up the sides of the metal enclosure. This problem is exasperated when the gauge of the wire is small compared to the size of the terminal block.
Rising Cage
A terminal block with a rising-cage style connection method.

A terminal block with a rising-cage style connection method.

Screw with rising cage clamp is my preferred connection type. This is where the bottom side of a square cage rises up and clamps the wire when you tighten the screw. This does not pinch and break the wire as often as the basic screw connection type terminal block does.


Spring-Loaded (Pogo) Connectors

Spring-loaded connectors (also called Pogo connectors after the similarity to a pogo stick), are connectors that use springs to push the pins of the connectors together to make an electrical connection. They are commonly used in scenarios where a fast, temporary connection is needed between two circuit boards (e.g. automatic test equipment/bed of nails testing devices, and in-circuit programming devices for microcontrollers).

Circular Connectors

DIN Connectors

The DIN connector was originally developed by the German National Standards Organisation. The known standards are:

  • DIN 41524
  • DIN 41612
  • DIN 43356
  • DIN 41652

DIN connectors with different numbers of pins can sometimes mate with each other. For example, 3-pin DIN connectors used for mono audio can mate with the left-channel of larger 5-pin DIN stereo connections. DIN connectors were used for the PS/2 keyboard and mouse connectors (know succeeded by the USB connector).

Mini-DIN Connectors

Mini-DIN connectors are smaller versions of the DIN connectors and are 9.5mm in diameter. A major difference between DIN and Mini-DIN connectors is that Mini-DIN connectors cannot be mated with any of different-number-of-pins Mini-DIN connectors.

Mini-DIN connectors have been used for the S-video interface.

Telecom Connectors

BT Connector

The connector called the “BT” connector (which is an acronym for the British Telecom connector) is commonly used through out houses in many countries (including the U.K. and New Zealand) to plug into a  Telecom jack that is mounted on the wall. It’s proper name is the BS6312 431A plug. You can get cheap BT to RJ-11 adapters.