USB HID device access from Xcode part 2

Building on the project in part 1, weíre going to expand our project to extract the deviceís Model and Serial Number!

Once again, Iíll be using an ONTRAK ADU208 as my test device, but similar steps should work with other USB HID devices too.

In part 1, we created a function that gets called every time a matching device is connected to the system. At present, this function simply logs the device ID to the console. Letís modify that function to store the Name and Serial Number, then log them to the console:


// New USB device specified in the matching dictionary has been added (callback function)

static void Handle_DeviceMatchingCallback(void *inContext,

                                             IOReturn inResult,

                                             void *inSender,

                                             IOHIDDeviceRef inIOHIDDeviceRef){

// Retrieve the device name & serial number

NSString *devName = [NSString stringWithUTF8String:





NSString *devSerialNumber = [NSString stringWithUTF8String:





// Log the device reference, Name, Serial Number & device count

NSLog(@"\nONTRAK device added: %p\nModel: %@\nSerial Number:%@\nONTRAK device count: %ld",






Youíll note that Iím using the IOHIDDeviceGetProperty function to retrieve both the Model and the Serial Number. IOHIDDeviceGetProperty returns a pointer to a CFTypeRef, which is not necessarily a string. Since Iím woking with an ONTRAK Control Systems ADU device, I knew the type returned would be a string. In a production application, it would be prudent to verify the type returned before assigning it to a string.

At this point you can go ahead and run your project - it will now log the device Reference, Model and Serial Number when attached to your system!

Download the Xcode 4 project file

This project was created on OS X 10.7.3 using Xcode 4.2.1.

Next time we will write to the device to open & close itsí relays!

View the next step.....Simple Read/Write For Ontrak USB Data Acquisition Interfaces ( XCODE )

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