USB - Connector Basics - SparkFun Learn

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USB Connectors

USB connectors come in two flavors: host and peripheral. In the USB standard, there is a difference between the two, and the connectors on cables and devices reflect this. However, all USB connectors will have some things in common:

• Polarization - A USB connector can only nominally be inserted one way. It may be possible to force a connector in wrong, but that will result in damage to the device.
• Four contacts - All USB connectors have at least four contacts (although some may have five, and USB 3.0+ connectors have even more). These are for power, ground, and two data lines (D+ and D-). USB connectors are designed to transmit 5V, up to 500mA.
• Shielding - USB connectors are shielded, such that a metal shell which is not part of the electrical circuit is provided. This is important to keep the signal intact in environments with a lot of electrical "noise".
• Robust power connection - It's important for the power pins to make connection before the data lines, to avoid trying to power the device over the data lines. All USB connectors are designed with this in mind.
• Molded strain relief - All USB cables have plastic overmolding at the connector to prevent strain on the cable that could potentially damage the electrical connections.

USB extension cable , with some of the common features of USB connectors labeled.

USB-A Connectors

USB-A female is the standard "host" connector type. This is found on computers, hubs, or any device intended to have peripherals plugged into it. It is also possible to find extension cables with a female A connector and a male A connector on the other end.

Female USB-A ports on the side of a laptop. The blue connector is USB 3.0 compliant.

USB-A male is the standard "peripheral" connector type. Most USB cables will have one end terminating in a USB-A male connector, and many devices (such as keyboards and mice) will have a built-in cable terminated with a USB-A male connector. It's also possible to find USB-A male connectors that are board mountable, for devices like USB memory sticks.

USB-B Connectors

USB-B female is a standard for peripheral devices. It's bulky, but robust, so in applications where size is not an issue, it's the preferred means for providing a removable connector for USB connectivity. It is usually a through-hole board mount connector, for maximum reliability, but there are panel-mount options for it as well.

USB-B connector, due to its low cost and durability.

Arduino boards, including this Uno , have long used the femaleconnector, due to its low cost and durability.

USB-B male is almost exclusively found at the end of a cable. USB-B cables are ubiquitous and inexpensive, which also contributes to the popularity of the USB-B connection.

USB-B male connector on the end of a SparkFun Cerberus cable

USB-Mini Connectors

The USB-Mini connection was the first standard attempt to reduce the size of the USB connector for smaller devices. USB-Mini female is typically found on smaller peripherals (MP3 players, older cellphones, small external hard drives), and is usually a surface mount connector, trading robustness for size. USB-Mini is slowly being phased out in favor of the USB-Micro connector.

USB-Mini female connector on a

connector on a Protosnap Pro Mini

USB-Mini male is another cable-only connector. As with USB-B, it's extremely common, and cables can be found cheaply almost anywhere.

USB-Mini male connector on the end of a

connector on the end of a SparkFun Cerberus cable

USB-Micro Connectors

USB-Micro is a fairly recent addition to the USB connector family. As with USB-Mini, the primary concern is size reduction, but USB-Micro adds a fifth pin for low-speed signalling, allowing it to be used in USB-OTG (On-the-go) applications where a device may want to operate as either a host or a peripheral depending on circumstances.

USB-Micro female is found on many newer peripherals, such as digital cameras and MP3 players. The adoption of USB-micro as a standard charge port for all new cellular phones and tablet computers means that chargers and data cables are becoming increasingly common, and USB-Micro is likely to supplant USB-Mini in the coming years as the small-factor USB connector of choice.

USB-Micro female connector on a

connector on a LilyPad Arduino USB board.

USB-Micro male is also a cable-only connector. There are generally two types of cables with USB-Micro male ends: one for connecting a device with a USB-Micro port as a peripheral to a USB host device and one for adapting the USB-Micro female port to a USB-A female port, to be used in USB-OTG capable devices.

USB-Micro male connector on the

connector on the SparkFun Cerberus cable

If you want to learn more, please visit our website AIKE Electronics.

Adapter pigtail for using USB-OTG capable devices having only a USB-Micro port with standard USB peripherals. Note that not all devices supporting USB-OTG will work with this pigtail.

USB 3.0 micro-B Cable

USB 3.0 micro-B cables look similar to USB 2.0 micro-B connectors but they include additional pins for two differential pairs and a ground.

USB 3.1 C Cable

USB C packs 24 pins into the USB connector. Unlike the previous versions predecessors, this version is reversable! The design of the USB C cable also allows for current above 500mA for your power hungry devices.

Heads up! Depending on the cable, not all of the pins are broken out for USB C. Some cables may be limited to the USB 2.0 specification with 4 pins as opposed to the full USB 3.1 specification. The

Depending on the cable, not all of the pins are broken out for USB C. Some cables may be limited to the USB 2.0 specification with 4 pins as opposed to the full USB 3.1 specification. The reversible USB A to C cables and SuzyQable are a few examples. Depending on the USB port that is used, you may also be limited in the amount of current that can be provided to your device.

Reversible USB

With the advancements in technology and manufacturing, USB connectors can be inserted either way! Below are examples of a reversible type A and type micro-b connector from the catalog.

If you are looking for a USB connector or cable, check out our USB Buying Guide or catalog.

USB Type-A connectors, officially called Standard-A connectors, are flat and rectangular in shape. Type A is the "original" USB connector and is the most recognizable and commonly used connector.

USB Type-A connectors are supported in every USB version, including USB 3.0, USB 2.0, and USB 1.1.

USB 3.0 Type-A connectors are often, but not always, the color blue. USB 2.0 Type-A and USB 1.1 Type-A connectors are often, but not always, black.

The part of the USB Type-A cord that plugs into a device is called the plug or a connector and the part that accepts the plug is called the receptacle but is commonly referred to as the port.

Lifewire / Tim Liedtke

USB Type-A Uses

USB Type-A ports/receptacles are found on almost any modern computer-like device that can act as a USB host, including, of course, computers of all kinds including desktops, laptops, netbooks, and many tablets.

USB Type-A ports are also found on other computer-like devices like video game consoles (PlayStation, Xbox, Wii, etc.), home audio/video receivers, "smart" televisions, DVRs, streaming players (Roku, etc.), DVD and Blu-ray players, and more.

Most USB Type-A plugs are found at one end of many different kinds of USB cables, each designed to connect the host device to some other device that also supports USB, usually via a different USB connector type like Micro-B or Type-B.

USB Type-A plugs are also found at the end of cables that are hard-wired into a USB device. This is typically how USB keyboards, mice, joysticks, and similar devices are designed.

Some USB devices are so small that the cable isn't necessary. In those cases, a USB Type-A plug is integrated directly into the USB device. The common flash drive is a perfect example.

USB Type-A Compatibility

The USB Type-A connectors outlined in all three USB versions share basically the same form factor. This means that the USB Type-A plug from any USB version will fit into the USB Type-A receptacle from any other USB version and vice versa.

That said, there are some significant differences between USB 3.0 Type-A connectors and those from USB 2.0 and USB 1.1.

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What is USB 3.0?

USB 3.0 Type-A connectors have nine pins, considerably more than the four pins that make up USB 2.0 and USB 1.1 Type-A connectors. These additional pins are used to enable the faster data transfer rate found in USB 3.0 but they are placed in the connectors in a way that does not prevent them from physically working with Type-A connectors from the previous USB standards.

See the USB Physical Compatibility Chart for a graphical representation of physical compatibility between USB connectors.

Just because the Type-A connector from one USB version fits in the Type A connector from another USB version does not mean that the connected devices will work at the highest speed, or even at all.

Frequently Asked Questions

If you want to learn more, please visit our website Standard USB 3.0 A Type Male Part.

• What's the difference between USB Type-A and USB-C? The USB-C is newer, slimmer, and more powerful than USB-A. Also, USB-C can potentially handle higher data-transfer speeds and is versatile, with Thunderbolt 3 compatibility. Another difference is that USB-C cables are reversible, which means there's no "up" or "down" side; you can just plug them in.
• My USB-A connector isn't working. Can it be fixed? Possibly. There are a number of troubleshooting steps to try to fix a malfunctioning USB-A port or connector. Hardware fixes include checking for debris or a loose connection, or you could be experiencing a software error that requires updating your system or rebooting.
• Is USB-A going away? While USB-C is newer and more versatile, many consumers and devices still rely on USB-A cabling and connectors. USB-A isn't going anywhere for a long while.