USB CablesUSB connections have two types of connectors, labeled A and B.
The A connector is a thin hollow blade, and the B connector is a hollow square (more or less).
The A connector is supposed to be on the end of the cable leading toward the computer, and the B connector leads toward the devices.
|There are a few devices that violate this standard, mostly
webcams. Do not use the "data transfer" USB cables to connect to
these devices. The data transfer cables have some embedded electronics
to change the signal packet, and that will make your webcam not work.
For these odd devices, you can either use a standard cable and an adapter, or use this cable 94-3984
- for an A to A
Some smaller devices, mostly digital cameras, have smaller, modified USB connectors. These are usually named "mini-B" connectors. Unfortunately, we have found at least 3 different proprietary connectors going by this name, and the only way to determine which one you need is by the picture. We do not have a list of which devices need which mini-B connector. More and more new devices are standardizing on one particular version, our part number 94-3996, so check that one out first.
USB LimitationsUSB is a system for getting (mostly) data and (a little bit of) power from your computer to a device and back again. To do this, USB is set up as a network, with your computer as the only place where all USB devices can talk to each other.
There are some limits to USB connections:
1. each USB cable can't be longer than 16 feet.
2. each USB device can't have more than 5 "nodes" between it and the computer.
3. each USB device shares the "data network" with all the other devices.
1. This limit has to do with the USB signal within the cables: 16 feet is the farthest they can go without running into timing problems. This is built into the USB Specification, and can't be changed. If you want to go farther than 16 feet from your computer, you'll need to have some specialized cables. Check out our USB Distance Extender page. If you want to put a long USB cable through a wall or a conduit or something, we really recommend the Ranger and Rover lines for the extension].
2. This limit has to do with the addressing scheme built into the USB network. This rule is pretty inflexible, and *must* be followed. A "node" is a hub, switch, or repeater, allowing another set of devices to be attached to the USB network. You can't plug a joystick into a hub into a hub into a hub into a hub into a hub into a hub into your computer, because that's six "nodes" between your joystick and the computer. There's not enough space in the addressing scheme for the computer to send or receive data from the joystick.
3. This limit has to do with what kind of speed you can expect from your printer, scanner, or USB webcam. A printer or scanner can (usually) stop and wait for the network to be clear before starting up again - a web cam can't do that, so if there's a printer or scanner (or USB drive or joystick or ...) on the USB network while a USB camera is broadcasting, you'll notice that the image stream will slow down and become more "jerky" as the other devices operate. This also affects CD burners that are connected through the USB port, so while you're burning a CD, don't try to print/scan/teleconference/etc - the burner won't get the data it needs on time. See "USB Data Limitations" below.
There are other limitations, but those depend on the device. For instance, we've had two reports that some Printer/Scanner/Fax combination machines will not operate the scanner if there's a "node" between the computer and the device, while the printer function operates perfectly that way. Please read your documentation thoroughly if you're going to alter your USB network, so you know just what your devices will allow, and what they won't.
There is a consistent problem with Lexmark multifunction printers and HP printers on the same USB network - the two manufacturer's printers don't "play well" with each other. The simplest solution for long term use is to install a second USB card on your computer, and attach one of the printers to that new card. This will create a second separate USB network, and the two printers should not interfere with each other.
USB Power LimitationsThe USB port supplies 500 milliamps on each connection. That power level will drop depending on distance and where the closest "externally powered" hub is. If you run a cable from your computer to a hub *that has no other power source*, then the 500 milliamps will be divided among the ports of the hub. If the hub has its own power connection, then there should be 500 milliamps from *each* of the ports on the hub.
Beware: not all manufacturers strictly follow the USB guidelines. But if your device needs power and isn't getting any, then you should either plug in your hubs or add an externally powered hub to provide power for your device.
USB Data LimitationsEach USB 1.1-equipped computer can handle about TWO Full Speed connections - that's 12 Mbps on each one (there *is* a superbly engineered USB 1.1 card that can handle a full 12 Mbps on all four connections, but that card has been discontinued). A USB 2.0-equipped computer will handle 480 Mbps on each channel, and they can handle about four of those at a time. If your USB 2.0 system is connected to just one USB 1.1 device, then the *entire* USB network will drop back to USB 1.1 speeds - so that's just two channels of 12 Mbps each, down from four channels of 480 Mbps each. Moral: it pays to check your cables and devices to make sure you're getting all the speed you can.
If you attempt to connect too many devices, so that the data limits are surpassed, the devices that are connected last will be disabled so they won't interfere with the devices that are already set up. If you want to check on the data requirements for your USB setup, we've got a table listing the typical data requirements for each type of device.
Please note that this information is not complete or definitive - different vendors will have slightly different requirements for their devices, and different uses will change that still further. But this table will give you a rough idea of what kind of devices can cooperate peacefully on one USB network. If you need more data capability, you can add another USB card for a completely separate USB network.
USB AdaptersThere are many older printers and other devices that do not have USB connections, and newer computers frequently do not come with the older, larger ports (like printer and midi ports). We carry some adapters that will allow these older devices to be connected to a USB-capable computer. This requires a driver so the signal can be correctly reconstituted after being converted to the USB format. Drivers are only available for Windows operating systems.
These adapters cannot be used to make older computers use a USB printer from their old printer port. The end with the USB connection must have a driver installed, and a printer cannot run the driver. The solution to this problem is to install a USB card into the computer. The only problem is if the computer is running Windows 95, because that operating system cannot cope with USB functions.
The USB Joystick adapter connects devices that used the old "gameport" or "midi" port via a USB connection. This adapter has been verified to work with most joysticks and has been verified to NOT work with Midi devices. We've had conflicting reports on how well it works with dictation pedals - most likely it depends on the model and manufacturer.
When converting keyboards and mice from PS/2 to USB, be sure that the computer is set up to look for the keyboard and mouse through its USB connection. Otherwise, it may refuse to boot or Windows may refuse to run.
USB Switches and HubsA hub connects one upstream device (like a computer) to several devices. The computer can communicate to all devices at the same time.
A switch connects one downstream device (like a printer) to several upstream devices (like a computer). Only one computer can communicate with the device at a time. Most switches are manual, which means that you have to turn the knob for another computer to reach the printer. The automatic switches take some time to switch over, so drivers that need fast feedback from the device won't work with this switch in the loop.
Gender Changers for USBSometimes a non-standard connection will require an odd cable configuration. Instead of carrying a large inventory of oddly configured cables, we carry a selection of gender adapters for USB cables. Please be sure that you order the correct combination of adapters - we want your projects to work, after all.
We also have a bendable extension for USB A-male connectors, for those situations when space is tight. This allows a 90 degree bend almost right out of the USB socket. We do not yet have these for USB B-male connections.
Motherboard ExtensionsMost current motherboards have USB functions built in, and need an adapter of sorts to allow USB connections. We have three of the most common types, and they can be further modified if you are able to determine the required pin assignments and make those changes. This is a more cost-effective solution than installing a new USB card, and can be used (by the technically inclined) to provide USB connections to locations other than the back of a computer case.
Power Supplies and Surge ProtectorsSurge protectors have a number of outlets and will protect all attached devices against power surges. Some models are able to filter model and cable connections as well.
Power supplies do everything that surge protectors do, but they also have a large battery to power devices for a short time after wall outlets shut down. The less expensive models only supply power to a few devices while providing surge protection for the rest. Because of the battery, these units are heavy, and can only be shipped by FedEx or UPS Ground.