It connects to and is powered by BrightSign's USB port.

Provides additional A/V ports for the HD810 and HD1010 models:
• 2 USB ports
• 18 bi-directional GPIOs
• Optical SPDIF output
• 3 analog stereo audio output
• Headphone output
• Connects to BrightSign via the USB port
• Can be powered by BrightSign via USB connection or included power supply
• Includes USB cable
 

For more information, please visit this products webpage.