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BlueTrack mouse revealed

Posted: 25 May 2009     Print Version  Bookmark and Share

Keywords:BlueTrack  blue light  CMOS image sensor 

Microsoft's latest mouse offers a window on new techniques in pointing and the durability of the mouse as one of the primary user-interface technologies. Starting with early prototypes in the late 1960s, the mouse has been around for quite some time and technical improvements ensure continued success. It works, it's cheap and it's intuitive.

As with any established technology, evolution is par for the course and with Microsoft's recent release of the BlueTrack family of mice, new approaches to lighting and image processing are brought to bear. As the name implies, blue illumination replaces the red or infrared light normally associated with optical mice.

Click on image to enlarge.

All optical mice share a common premise in operation. The surface on which the optical mouse rests is lit up by an angled LED—usually by way of some optics to translate a point source into a larger area of illumination. The light bouncing off the mousing surface is in turn directed to a second angled lens, which focuses the reflection from the illuminated region onto a relatively low-resolution image sensor. Despite the modest pixel count, image processing is able to discern movement by "reading" the fine features of the mousing surface and determining the relative direction imaged features move across. By watching the scenery pass by, the mouse knows which way it's being moved.

But as most of us know, the surface on which the mouse rests makes a vast difference in mouse response. Without surface variation or pattern to be tracked, the mouse may budge but the cursor may not. The Microsoft solution to improve the range of usable mousing surfaces lies in both replacement of the traditional red/infrared LED—quite often a laser LED—with a non-laser blue source and proprietary optoelectronics.

The choice of blue light is claimed to provide for higher contrast images and at some level behave similar to ultraviolet light to where hidden detail is brought out (think crime-scene forensics). Microsoft also uses diffusion of the source LED to provide a more uniform light flux over the illuminated area.

After removal of a hidden screw here and there the BlueTrack mouse can be opened fully up, the LED used for tracking is a simple-enough looking leaded part with the optical moulding compound being a translucent milky encapsulant for achieving diffusive properties. Several other blue LEDs ring the mouse but their purpose is just decorative, illuminating the product logo or piping through a light guide around the enclosure for a halo effect.

The other half of the optical chain is a CMOS image sensor and image processor ASIC, seemingly designed by and made for Microsoft. A built-in window in the sensor package allows the reflected image to reach the device's 24x24 pixel array—low resolution by imaging standards but adequate for the intended purpose. Because the part has control and processing duties along with imaging—all on a budget of two AA batteries—a small array reduces power and likely improves the rate of frame processing possible at a given power consumption. A 32-Kbit (4 KB) EEPROM from Atmel is used by the ASIC for embedded code.

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