Believe it or not there’s actually a USB Host shield for the Arduino. The shield and accompanying libraries will let you communicate with USB client devices… like this USB digital scale. Normally this USB digital scale is plugged into a PC which will read the weight (I assume for weighing packages for mailing).
Oleg decided to to add an LCD to the device so it could be used stand alone. He’s using your run-of-the-mill 16×2 hd44780 compatible display, an Arduino, and the USB Host shield. The scale reports itself as a HID device to the host but still a little reverse engineering was needed to extract the weight information from the HID report. Once the target packets were identified, Oleg whipped up a sketch to read the USB report packets and throw the info out to the LCD display.
I probably wouldn’t have the patience for doing it this way, I would have tried to open it up and read data from one of the sensors directly, but this hack just introduces you to another vector of modification or input method. For instance using a USB joystick or flight stick with the USB host shield might be a great addition to a flame-throwing robot or something (lol).
Source sketch and more info here.