Inside Xbox 360's Kinect controller

Machine vision meets home entertainment in the Kinect sensor peripheral for Microsoft’s Xbox 360. Kinect puts the players in the game by eliminating the game controller altogether.

Fabless semiconductor company PrimeSense (Tel-Aviv, Israel) enabled the technological feat via its PrimeSensor reference design, which it says lets a computer “perceive the world in three dimensions and translate these perceptions into a synchronized image.” In the approach, the room and its occupants are peppered with a pattern of dots, unseen by the users and generated by a near-infrared laser; the use of a Class 1 laser device provides focus at a distance without hazard to the players.

A CMOS image sensor detects reflected segments of the infrared dot pattern and maps the intensity of each segment to a corresponding distance from the sensor, with resolution of the depth dimension (z axis) down to 1 centimeter. Spatial resolution (x and y axes) is on the order of millimeters, and RGB input from a second CMOS image sensor is pixel-aligned to add color to the acquired data.

The Kinect uses the three-dimensional position and movement data to produce corresponding on-screen movements by each player’s avatar. A motorized gear assembly keeps the image sensors aimed at the action; as players move, the Kinect follows. Four microphones are used to cancel echoes and background noise while helping determine which player has issued a voice command. It’s not too hard to think of other applications for this technology, but for now it’s available as a video game interface.

Microsoft expects to sell a few million Kinect units by the end of the year, so it comes as no surprise that several of the commodity components appear to have second and third sources in play. For example, the 64-Mbyte DDR2 SDRAM socket has been shown to contain equivalent parts from Samsung, Elpida and Hynix in three different Kinect units. Likewise, 1-Mbyte NOR flash from Silicon Storage Technology occupies a slot on one of our Kinect units, while the same slot is filled by STMicroelectronics on another.

The Kinect contains plenty of op amps and other small components, also likely candidates for multiple sourcing. Thus, the contents of your Kinect may vary.

Nonetheless, here is what we were able to determine from our teardown.

The “eyes” of the Kinect are a pair of cameras, both of which incorporate CMOS image sensors from Aptina Imaging. The infrared camera uses the MT9M001 sensor, an older model presumably chosen for its relatively large, 5.2-micron pixels; larger pixels do well in low light and, with correct filtering, lend themselves nicely to infrared applications.

RGB input comes courtesy of the color camera, featuring the MT9M112 sensor. Both sensors claim 1.3-megapixel resolution, meaning that downscaling was employed for interface with the PrimeSense PS1080; that “sensory processing” system-on-chip controls the infrared projector, processes inputs from the cameras and collects audio input.

In turn, the PS1080 is in communication via USB 2.0 with the application processor, a Marvell product whose Aspen die mark gives it away as the PXA168—a low-power, low-cost gigahertz-plus screamer that should have tech-frenzied gamers swooning. Rounding out the key input devices is a pair of Wolfson Microelectronics WM8737L stereo A/D converters, with built-in microphone preamplifiers to accommodate the aforementioned array of microphones.

The Kinect also houses a MEMS accelerometer, the Kionix KXSD9; since the unit has a limited range of motion, this is presumed to be part of the tilt-control loop, which also includes the A3906 stepper and dc motor driver from Allegro Microsystems. Other noteworthy components include the uPD720114 USB hub controller from NEC and a pair from Texas Instruments: the TAS1020B USB audio streaming controller and ADS7830 8-bit, eight-channel A/D converter.

Perhaps more interesting than the component makeup of the Kinect is the fact that all this capability can be had for $150. At the time of this writing, hackers were racing, with apparent success, to create open-source code for the Kinect. Microsoft may not endorse the practice, but clever individuals, including some of the habitual warranty voiders who read Under the Hood, will be creating their own applications any day now.

Meanwhile, those with less time on their hands can envision possibilities beyond the Kinect: a TV with no remote; a computer with no mouse, no trackpad and no touchscreen; affordable advances in home security; and any number of aids for the elderly and disabled. Whether you run off and attach your Kinect to a homemade robot, limit its use to its intended gaming purpose or do neither, you’ll be seeing this technology again.

About the author

Bob Widenhofer is a senior product analyst at UBM TechInsights-Austin, producing teardown reports and related industry research on wireless, mobile and personal electronics.

Click on image to enlarge.

Click on image to enlarge.