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USB in the Classroom — USB in an A/V World

Universal Serial Bus (USB) is an industry standard developed in the mid-1990s that's used for connecting computer peripherals and providing power to various electronic devices. It was designed to standardize the connection of keyboards and mice, cameras and scanners, printers and portable drives to personal computers. USB quickly replaced serial and parallel ports on computers, and it wasn't long before the convergence of data and audio/video signals, led by the popularity of the Apple® iPod®, allowed USB connectivity to nearly erase the lines between communication, computing, and media presentation technologies. Today USB compatibility is a vital aspect of any A/V installation—and your project isn't complete if you haven't considered how USB will impact the utility of the system.

The three USB standards commonly encountered are USB 1.1, 2.0 and 3.0. Understanding how they differ and how they'll evolve is critical to successful system design. USB 1.1 was released in 1998 and provides up to a 12 Mbit/s data rate. This is ideal for transferring files from drives, playing back relatively low resolution video or audio files, and interfacing with control devices such as the touch sensitive surface of an interactive whiteboard. In 2000, the USB 2.0 standard was released. It upped the speed limit to 480 Mbit/s—forty times faster than USB 1.1. USB 2.0 can provide moderately high quality video and very high quality audio playback along with seamless integration of high density data drives. USB 3.0, with its blistering fast "SuperSpeed" bus and potential 5 Gbit/s transfer capability, offers the highest level of performance, but with the added requirement of thicker, heavier cables and connectors that have twice as many conductors. With USB 3.0 there is an attendant reduction in useable connection length. The maximum practical length for USB 3.0 connectivity over copper is about 10 feet.

In the A/V presentation world there is seldom a real need for USB 3.0 capability. In fact, USB 1.1 speeds are often sufficient. But when multiple signals are combined on a single bus, such as when the user interface of a touch screen is combined with the sound files used to drive a pair of USB speakers, then the limitations of USB 1.1 can be quickly reached. Indeed, any good design that is properly anticipating the continued growth of USB enabled A/V devices should be designed to a USB 2.0 standard to ensure unhindered performance for the foreseeable future.

The real tripping point of USB in an A/V system comes with the need for power. USB 1.1 and 2.0 specifications provide 5 volts, +/– 5%, to power connected devices. As you know, power is the product of voltage and current. In the USB standard, power is specified as a "unit load" of 100 mA and any single device can draw a maximum of 5 unit loads, or 500 mA. USB 2.0 connectors are rated at a maximum of 1.5 A, three times the maximum unit load. Since power is most often supplied to the USB network by the host computer, excessive power demand—if unregulated—could potentially cause problems with the computer power supply. Computers have power regulation circuitry to avoid such damage by limiting current and voltage output. When a connected device exceeds the maximum power capability of the host, intermittent loss of performance or outright failure of the signal is often the reward.

The USB standard allows for higher power delivery (up to the maximum 1.5 A) for charging ubiquitous smartphones, media players, Bluetooth® accessories and other gizmos while simultaneously sharing data through the inclusion of charging ports. Most often a computer will utilize a downstream charging port, which combines data transfer with high power delivery. But, since we can seldom predict when designing a system what peripherals will be connected (who could have predicted the proliferation of smart tablet devices such as the iPad® three years ago?) over the life of the installation, it would be unwise to assume that a host computer with a bus-powered hub will always suffice. Instead, a self-powered hub, where the USB hub has an independent power supply capable of supplying maximum supported unit loads to any and every device connected, is often used.

Finally, there is the issue of cable length. USB 2.0 provides for a maximum cable length of 5 meters. The primary reason for this limit is latency. If USB host commands are unanswered by the USB device within a specified time, the host considers the command lost. Since 5 meters is seldom sufficient to encompass the structured aspects of an A/V installation, and because standard USB cables are seldom available with in-wall or plenum ratings, USB extender devices that leverage the UTP environment are the best choice for most permanent installations.

For the ultimate in dependable USB performance for A/V installations involving permanently mounted interactive whiteboards, interactive touch-sensitive displays, or the integration of document cameras, scanners or USB speaker systems and other USB devices, a USB 2.0 active extender system may be employed. Systems of this type adapt the USB signal to a Cat5e or Cat6 structured wiring and allow dependable runs up to 328 feet.

The C2G USB 2.0 Superbooster Wall Plate Kit is a great example of a unique and useful solution for solving USB challenges in demanding A/V projects. At C2G we have a full selection of USB hubs, boosters and cables for all of your USB 1.1, 2.0 and 3.0 connectivity needs.

USB Superbooster Wall Plate Kit In Action

This white paper is for informational purposes only and is subject to change without notice. C2G makes no guarantees, either expressed or implied, concerning the accuracy, completeness or reliability of the information found in this document.