My final goal is to use the mbed standalone with a USB keyboard and a LCD display and no usb connection to the desktop computer.

Yesterday I got USBHostShell working properly with the USB keyboard. Today I disconnected the usb cable from the desktop and the USB host interface quit working. The mbed is still powered up (from my external source) and is running the program (the LCD is doing periodic things as expected). The program resets normally, but the USB Host interface just will not work until I reconnect the USB cable to the computer.

So it appears as if there is a dependency on the USB connection to the desktop somewhere in the USB Host interface.

My program has many pc.printf statements and I would think they just dump bits into the bit bucket but should have no effect on the USB Host interface. I will have to start experimenting of course, but can anyone tell me if I should be able to use the USB Host interface in a stand alone environment, with no dependency on a connection to a desktop host?

Thanks.

Chuck

Is it a power issue? The VU pin on the mbed only provides power out when there's a USB connection. If it's not connected you need to get a 5v source from somewhere else.

Matt

Hi Matt,

Yes, that is the problem! I realized it the moment I read your reply. I should have remembered that I "temporarily" hooked up the power for the USB keys to that pin on one breadboard that had no external power. I then blindly duplicated that wiring in the one where I do have external power available (which is where I did this test).

Many thanks. Your reply just saved me who knows how much time before I would have finally realized what was going on.

Chuck