用android设备控制电机

I am trying to get a custom android app (running on a Packard Bell "liberty tab", android 3.2) to control an external motor. No need for fine control, just a way to signal "on" and "off". Which port on the device can I use to get that output, and how do I program it? Being able to simply turn on or off the power on the USB would be perfect, but I read an answer to another question on this site that told me it is not possible with android.I am trying to get a custom android app (runnin