How to communicate with a USB device?

That string is just a marker so you recognize the intent that is returned when you call registerReceiver(mUsbReceiver, filter);. That isn't the problem.

I think the problem is here:

UsbManager mUsbManager = (UsbManager) getSystemService(Context.USB_SERVICE);

This line is supposed to get you your USB Manager, but as far as I recall not all phones have to support the Android USB Accessory API. This line is probably just assigning null to mUsbManager which then causes you NullPointerException when you call a method on it further down in the code. Trying checking if that isn't null before making a call on it.

For more info, checkout these links:

1. http://developer.android.com/guide/topics/usb/index.html
2. http://developer.android.com/guide/topics/usb/accessory.html

EDIT:

I think I see what the issue is now. You're right, it's not the USB Manager. It's the UsbDevice object (device). It is never initialized anywhere in your code. In this line :

mUsbManager.requestPermission(device, mPermissionIntent);

you're basically firing off an intent to ask the user if it's okay for you to work with the device represented by the UsbDevice object device. However when this call gets fired device has not yet been initialized (and therefore has the default value of null). So when you try to request permission you end up getting a NullPointerException instead of the expected result. To fix this you need to figure out which device you want to connect to and assign it to device. Look in here, under "Enumerating devices" to figure out different ways to do that. One way, if you know the name of the device you want to connect to, is to make the following calls after you retrieve the Usb Manager:

HashMap<String, UsbDevice> deviceList = mUsbManager.getDeviceList();
device = deviceList.get("<deviceName>");

(Obviously, you would replace <deviceName> with the actual name of the device.

minSdkVersion must >= 12

To enable USB host API support you should add a file named android.hardware.usb.host.xml and containing the following lines:

<permissions>
 <feature name="android.hardware.usb.host"/>