USB Power + Wireless bridge

[ctwilliams]

My company notebook has the internal wireless card disabled and the system locked down tight. I would like to use it with my wireless network. I can not use any type of USB network device since you have to install drivers.

What I would like to do is use a wireless bridge such as the Linksys WET54G. This will work without my having to install any drivers on the system. This comes with a power adapter or can use power over Ethernet. The specs list input voltage as five volts.

Instead of having to plug this bridge in to AC power everywhere I go I would like to power it from a usb port on the computer.

From what I have read the USB output is five volts and devices must be less than 1000ma.

Can I take the raw output from a usb port and put it straight into a device such as this bridge? Or will there be a slow melting of my new bridge and/or notebook?

Any ideas?

 

[rocco]

Hi. ct:

I foresee a couple potential problems with trying to use USB for power.

The first is that the USB uses "managed" power. According to the spec, when a device is plugged in, it may draw no more than 100 milliamps of 5 volts. During the initialization handshake, the device can request up to 500 milliamps, but the request may or may not be granted. In any case, the USB host or hub is required to detect and limit any over-current situation, for safety reasons.

The one thing working in your favor is that I have seen many USB host adapters that simply wired the 5 volts from the PCI bus directly to the USB through a resettable fuse. Though it doesn't adhere to the spec, who's going to care as long as the power was available?

The second potential problem is with the voltage. Many 5 volt devices require regulation within +/- 5%, which means a minimum of 4.75 volts. The USB power is rarely a full 5 volts, and as specified, can be as low as 4.40 volts at the device. It is designed to power locally regulated 3 volt logic.

Finally, I would think twice about using your laptop on your wireless network. At a previous company, I was required to terminate any employee who had compromised the security of their laptops. It was considered a very serious offense.

 

[ctwilliams]

I foresee a couple potential problems with trying to use USB for power.

The one thing working in your favor is that I have seen many USB host adapters that simply wired the 5 volts from the PCI bus directly to the USB through a resettable fuse. Though it doesn't adhere to the spec, who's going to care as long as the power was available?

The second potential problem is with the voltage. Many 5 volt devices require regulation within +/- 5%, which means a minimum of 4.75 volts. The USB power is rarely a full 5 volts, and as specified, can be as low as 4.40 volts at the device. It is designed to power locally regulated 3 volt logic.

Finally, I would think twice about using your laptop on your wireless network. At a previous company, I was required to terminate any employee who had compromised the security of their laptops. It was considered a very serious offense.

That is good information. I think I will try it with a more disposable USB port on another computer first. I wonder how tight this bridge is as far as the voltage it needs. I have found plenty of USB powered network devices so I assume that it is possible, I just dont know if this particular one requres more power than they would for some reason.

As for the using it on my wireless network, very true in most situations, but long story short, in this case I have the ok.

Thanks for the info!

CT