USB ports


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Old 01-23-08, 03:11 PM
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USB ports

To make a long story short, new computer, doesn't have serial port, I got a serial to USB adapter to upload data from a blood glucose tester. After working with the software maker and tech support at the USB manufacturer(keyspan) it turns out to be a known problem that some deviced do not work if plugged in to a USB port on the keyboard, or on the front of the tower, or to a HUB. They only work if plugged into a USB port on the back of the tower.


That solved my problem. I am not a computer teckhy type, but am curious if there is a simple explanation of how that works. It was not explained to me if the issue it the new computer, the software, or the serial to USB device.
 
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Old 01-23-08, 06:44 PM
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It could be the mother board USB port is powered, and the others are not.
 
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Old 01-24-08, 12:21 AM
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Lightbulb USB Power

Oneofamill is likely correct. USB ports are not all created equal.

USB ports can provide power as well as a data transfer medium for many devices. Some devices will let you use it for data transfer or power, but not both at the same time. As you have discovered, not all USB ports provide the same power.

Devices like mice and keyboards are certainly getting power from the USB connections, but don't have a lot of power requirements. I have plugged a mouse into a keyboard, but most of my PC toys are not satisfied by this.

You can see the power being provided by USB hubs on your system by right clicking My Computer and choosing Manage. From here, pick Device Manager on the left and then on the right pane of the window scroll down till you find Universal Serial Bus Controllers.

Expand this, and look for items like USB hub or USB root hub. Double click a hub to see the properties. The Power tab tells you how much power that particular hub provides and what is being used.

There is a limit to the power provided over an unpowered USB hub, and not all powered hubs provide the same power. Whether this causes a problem or not depends on the device you are plugging in. Your operating system/USB drivers may tell you when you plug in a device that the port doesn't supply enough power.

My Bluetooth hub provides 100mA (milliamps) per port and my mouse and keyboard are using 98mA each. By contrast the root hub of my PC provides 500mA.

The ports in the rear of your system are being powered through the system. If you have ports on the front, they are likely to be as well. Your keyboard is not.

The good news if you run out of powered USB ports is that you can buy a powered USB hub as an internal add on card, or an external device with its own power supply. I have ports on my monitor, which get powered through it's power supply.

There are options if you have power hungry USB peripherals.
 
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Old 01-24-08, 08:17 AM
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Thank you very much for taking the time to explain this. I understand now that all ports are not equal, and I can work with that.
 
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Old 01-24-08, 06:08 PM
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There is also an issue of USB 1.0 versus 2.0 for both compatibility and speed. Most of that has been resolved on the newer machines, but when they first came out a few years ago, USB 2.0 devices wouldn't work on a USB 1.0 connection.

You can insert your own power to a USB device by clipping & capping the DC power wires from the computer and substituting a regulated wall wart to the device. Pins 1 and 4 are usually +5VDC and ground respectively.

The other two pins are just serial data + and -.

Here's a good site that has pinouts for common connectors. Understanding the connections isn't rocket science. Figuring out how 1/2-inch diameter fingers deal with those .004" wires is.
 
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Old 01-24-08, 11:41 PM
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It's very common to have problems with the USB to serial converters, depending on the device you are converting to. As a systems integrator, we run into it alot. Probably 25% work with no problem, and of the rest, half we can figure out and half require calling tech support. Not a very smooth system. And it is very difficult to find laptops especially with serial ports. Dell has them on the Latitudes, which cost at least $100 more than an equivialant Inspiron model, or whatever is current.
 
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Old 01-25-08, 06:33 PM
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Thank you for that. I have a Kodak mini printer, for photos. It prints fine directly from the camera, but never could make it print from files on the computer. I was hooking it up to a powered hub. I will try connecting it right to the back of the new tower, and see if it works.
 
 

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