USB connection to Bsic Stamp gives "power surge" on PC

[Brian Newport]

Started building the BOE-Bot with BASIC Stamp and USB interface last week. Got as far as downloading and running a program that turns the wheels, but started getting intermittent "Power surge on hub port" error on Windows XP. This error has to be cleared by unplugging the USB cable and clicking on the message.

Unfortunately this is now a permanent problem. The power surge occurs whether or not the Stamp is powered, and does not happen with just the cable alone. I'm guessing the 5 volt USB power line has a short to ground on the board, but can't confirm this without a circuit diagram. The circuit diagram that came with board does not show enough detail in the USB interface area.

I did try reinstalling the USB driver. As I expected this did not help.

I don't know how I could have fried the USB interface so easily ...

[Franklin]

This should help http://www.parallax.com/Portals/0/Downloads/docs/prod/boards/BOE_USB_D_Schematic.pdf

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- Stephen

[Mike Green]

Please note that power from the USB connection is used in very limited ways:

1) To power the FTDI chip
2) To power the two signal LEDs for RX and TX
3) To power the transistors that provide the ATN and SIN signals

These last two do go to the Stamp and it's possible for there to be "sneak"
paths through the Stamp programming interface (see the Stamp manual
for a schematic) to where there might be excessive current draw that way.
The FTDI chip is supposed to limit the amount of USB +5V that can be drawn
so it may be damaged somehow.

[Brian Newport]

Stephen and Mike,

Thanks for your help.

Stephen - I downloaded the schematic, makes sense.

Mike - Thanks for confirming my my guess about how this was supposed to work.

Will investigate further next time I work on it.