DB9 D-Subminiature Connectors : Advantages and Disadvantages

June 19, 2013 at 10:00 AM

9-pin D-Sub connectors (DB9 or DE-9)

 

DB9 Connector on Cable

For many years, serial communication was one of the chief methods of connecting peripherals (such as joysticks, printers, and scanners) to PCs. The most common connector type for serial communication was the 9-pin D-Subminiature connector, or sometimes called a DB9 or a DE-9.

 

Nine pins were plenty to carry the data in series, and though there were many drawbacks to DB9 connectors which eventually lead to them becoming legacy in favor of standards like USB, there are still many devices with DB9 ports or cables on them today.

 

 

What are the disadvantages?

 

The connectors themselves are large, making them difficult to connect and disconnect in tight spaces. Also, the pins are exposed in the shell, so they can be easily bent or broken off. Though the connector can be mated without using the thumbscrew hardware, it does not tend to hold as well using just friction-fitting. If you do use the thumbscrews, the connector takes much longer to plug in and unplug.

 

Finally, serial communication tends to be slow, especially over longer lengths, and unexpected breaks in communication could cause software on the PC to freeze. All of these problems led to other standards becoming more popular for the same applications.

 

However, this does not mean that the DB9 connector is a lost cause. There are actually solutions available for many of the problems mentioned above. For instance, right angle adapters solve the tight-space problem by allowing a tight angle without damaging the connector. Widely available D-Subminiature plug and jack covers can protect pins from damage when not mated, and adapters like gender changers and socket savers can reduce the stress caused by repeated mating cycles.

 

 

On the other hand...

 

ES4-232 4-Port Ethernet to DB9 Adapter and Device Server

DB9 connectors have advantages too. In general they are far easier to customize, with at least 9 individual pins to carry serial data. Though the speed is slower than other standards, the length of the cable can be much longer. USB, for instance, has a five-meter length limit, but RS-232 (the most common standard for serial data) has no defined length limit, and RS-422 has been used at lengths hundreds of meters long with special equipment.

 

Also- Don't worry if you have an old device that only has DB9 connectors on it. Even with D-Subminiature being mostly legacy, there are plenty of options for conversion. Converters to and from USB, Ethernet, and other standards are common and can allow you to use your device on any computer today.

 

Examples of Applications for Serial Converters

If you're looking to find DB9 Connectors: L-com carries products ranging from economical serial cables with many off-the-shelf lengths to high-quality premium cables for demanding applications. Also check out L-com's D-Subminiature adapters for innovative solutions to common problems, and L-com's bulk cable, connectors, adapter kits and tools for do-it-yourself components.
 

Cat 6 Shielded vs. Unshielded

June 5, 2013 at 10:00 AM


Category 6 cable with drain wire

Category 6 or Cat6 Ethernet cable is designed to provide up to 1 Gbps Ethernet transmission, and is required for 1000 Base-T style networks. However, the choice to use unshielded twisted pairs (UTP) or shielded (or screened) twisted pairs (STP or ScTP) depends on the location of the installation.

 

Typically, the shield is only required in cases where the cable is run through an area of high electro-magnetic interference or radio frequency interference (EMI/RFI), such as output by strong power lines, motors, magnets, and radio antennas. Outside of these situations, the shield does not help provide a faster or clearer signal, and can add more problems than it solves.

 

Pros and cons 

 

Without a shield, Cat 6 UTP cable is already resistant to minor and typical forms of EMI/RFI, such as having a fluorescent light or small motor nearby. In these cases, you should always run the cable at a 90° angle to the source of the interference in order to minimize exposure. Otherwise UTP is cheaper, lighter, and just as effective as STP.

 

If you need STP cable, you have to remember that the shield itself must drain, otherwise EMI/RFI can build up on it and degrade the signal inside. Drainage is typically done at the connection site by using a shielded coupler or jack that is connected to ground.

 

Also note that the weight of shielded cable, while not very heavy, can be significant if you are running multiple cables in an area. In some cases, heavy cabling run above a ceiling or behind a wall has caused collapses and structural damage over time.

 

Quick note: Visit L-com's Ethernet Product Center for a huge selection of common and hard-to-find Ethernet cabling solutions, including shielded, harsh-environment, special jacketed and more.

A Tutorial on USB

May 22, 2013 at 10:00 AM

 

What exactly is USB?

USB Cable

 

USB stands for Universal Serial Bus and is a connectivity standard that transfers large amounts of data between devices. While it is far from the first standard designed for this purpose, the need for an effective method to transfer data between devices has become enormous due to the increase in portable and mobile devices.

 

The USB standard does just this, providing a universal method across different products and manufacturers. Other, "proprietary" standards exist, but they are often derivatives of USB with slight changes to the wiring or physical connector type.

 

 

Types of USB Cabling and Connectors

 

In the years since USB was first implemented, there have been three dominant versions, each providing faster data throughput than the last. USB 1.1, sometimes called "full-speed", can transfer data at about 12 Mbps. USB 2.0, which is currently the most common, operates at 480 Mbps. The latest standard, USB 3.0, operates at over 4.8 Gbps (about 10 times that of USB 2.0).

 

The most common USB connector types, Type A and Type B, are the same throughout the different versions. Though, other connector types such as the Mini B4, Mini B5, and Micro B are gaining popularity for their small size, which is preferred in smaller portable electronics such as mobile phones and tablets.

 

However, even if the connectors are similar, the cable itself must be constructed to the standard. For example, a USB 2.0 compliant cable could not pass 4.8 Gbps of data even if it were plugged into a USB 3.0 compliant device.

 

 

Why is USB so popular?

 

USB has several advantages over other standards that are used for the same purpose. First, it is a "hot connection", or has the ability to plug and unplug into a computer without causing it to freeze or causing programs to crash. USB is also uniquely designed to carry some low-voltage power which makes it capable of powering or charging devices that it is plugged into.

 

Also, though most applications only need standard USB cables, another advantage of USB is that it has the capability of specialization. Today we are seeing a rapid expansion of USB applications which require more specialized cabling- outdoor, wet or dusty environments, high-vibration situations, and places where special flame ratings, armor, or angled connectors are required. 

 

Check out our detailed USB tutorial here. Or, if you find yourself in this kind of special situation, try browsing L-com's USB product center for innovative solutions.

 

How To Differentiate VGA, SVGA and UXGA

May 8, 2013 at 4:38 PM

 

VGA Cable

While knowing these specific terms is helpful in buying some analog display equipment (such as computer monitors), each refers to the same type of video format. These acronyms relate to the resolution a monitor supports, thus the same type of cabling and connectors are used.

 

Another common denominator with VGA, SVGA, and UXGA is that they are all mostly now legacy. No new products are being built using VGA analog video interfaces. 

 

However, if you have irreplaceable or expensive equipment that requires using VGA analog video, you'll find it useful to know its functionality. 

 

Typical VGA cables have a high-density fifteen-pin (HD15) connector on each end, using a combination of mini-coaxial cables and straight or twisted pair conductors to carry a video signal. VGA does not include audio support like HDMI® and DisplayPort cables do.

 

What do these terms mean? VGA stands for Video Graphics Array. As video display equipment that used the VGA standard became more sophisticated, manufacturers began adjusting the name of the standard to reflect the maximum resolution of the display device. For example, SVGA stands for Super Video Graphics Aray which supports a resolution of 800 x 600. As the list grew, it became easier to just list the maximum resolution rather than the letters that corresponded to it.

 

Today, there are over 20 different letter combinations referring to all sorts of different resolutions, a list of which can be found here. Most of these terms are rarely used to refer to analog video equipment anymore. And as mentioned previously, the standard itself is rapidly becoming legacy in the face of digital video standards such as HDMI®, DVI, and DisplayPort.

 

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Using Latching USB Cables for Vibration-Proof Connections

April 24, 2013 at 10:00 AM


Latching USB Cables

One of the most successful connectivity technologies is Universal Serial Bus or USB 2.0. Why? You can find it everywhere, from laptops and desktop computers to peripheral devices like printers, mice and keyboards, to consumer electronics like cell phones and camcorders. 

 

(Click here for a tutorial on USB technology.)

 

Surprisingly though, there are some fundamental problems with USB 2.0, one of which is its sensitivity to vibration.

Latching USB Drawing

 

USB 2.0 uses what's called a "friction fit" to remain connected, which means the friction between the connector and the jack is all that holds the connection together. As you'd find with vehicles and in military/aerospace applications, vibration can cause connectors to unexpectedly separate.

 

L-com has countered this problem by offering "latching" USB 2.0 cables.  The latches, which are on the sides of the connector, fit into any standard USB 2.0 female jacks.  Currently latches are only available on USB 2.0 Type A male connectors and they come standard on micro-B male connectors. L-com offers:

 

 
 
Quick note: Latching connectors are also available for SATA cables.
 
Additionally, L-com now offers USB 3.0 cables with locking thumbscrews. These cables can be used in machine vision applications or with any application where vibration is an issue.
 
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