Advertisement

Article

Under the Hood: Gyro sensor liberates mouse

At the suggestion of Wireless DesignLine site editor Jack Shandle, we embark this week on a teardown of a gyro-based mouse: Gyration's $150 ProGo Gyrotransport (which includes a free-space mouse as well as 1 Gbyte of “playing around” storage within the separate USB transceiver dongle on the host PC). For those unfamiliar with this sort of product, it's a fairly easy-to-use pointing and control system based on free-space movements and gestures. Wave the mouse across or through an imaginary canvas, and your on-screen cursor tracks; hover at a link and click the button. All very handy when you're presenting or otherwise away from the desk.

For a full archive of articles and related On-Demand seminars, click here

I have to admit to a sidebar problem in setting the thing up: I was ready to call for support when I couldn't get the two-button pairing action between the pieces to take. But then I discovered a thin, clear wrapper left on the AAA battery that powers the mousing device. Call it poor design (possibly) or user inattention (probably), but after that little problem was out of the way, it worked like a snap.

1-Gbyte NAND flash drive memory

The small USB transceiver on the PC side communicates to the mouse on a 2.4-GHz link while hosting a gigabyte of NAND flash drive memory. In the unit analyzed, an MT29F8G08FAB 8-Gbit (1-Gbyte) NAND package from Micron Technology stacks four 256-Mbyte SLC NAND chips in a TSOP to add a bonus to an already handy gadget. To make the memory usable as a flash drive, a Cypress CY7C68033 USB NAND flash controller handles both the USB and memory interfaces.

Joining the controller and memory is Cypress' CYWUSB6953, which creates half of the 2.4-GHz wireless link needed to communicate with the airborne mousing device.

The mouse is powered by a Texas Instruments mixed-signal microcontroller (the MSP430F1232) that has 8 kbytes plus 256 bytes of flash memory and 256 bytes of RAM.

Along with a TI boost dc/dc converter, the mouse contains the other half of the 2.4-GHz wireless link in the Cypress CYWUSB6934 2.4-GHz direct-sequence spread-spectrum radio system-on-chip.




Although the Cypress WUSB part is an impressive item from the chip world, an equally intriguing part in the mouse is the MG1104 gyroscope module from Gyration. Gyration is owned by Movea, a funded spinout of Thomson of France, which still holds a minority stake.

The MG1104 was a surprisingly large and different sensor from what I expected to find in this era of silicon-microelectromechanical-system (MEMS) accelerometers. The large-sugar-cube-sized module (about 14 mm to a side) hosts semiconductor content, but only in a supporting role to the gyro sensor itself. The gyro's operation is based on some common physics in the form of the Coriolis effect.

I reluctantly use the the “common,” because I was slow to figure out how the physical gyro structure uses the principle. The critical aspect seems to be the Coriolis effect's ability to deliver horizontal and vertical acceleration from the velocity of the rotation and oscillation of the gyro plate when it is moved.

The transducer is an etched metal plate that forms an intricate web of fingers from a driven center point. At first glance, it resembles the old inserts used with 45-rpm vinyl albums to allow them to be played on standard LP spindles (I know, I'm dating myself). The plate is coupled to a driver coil that sets up a fundamental oscillation, and freestanding spokes in the plate seem to be the points of monitoring for a second, more-complex set of oscillation modes. A poor showing in freshman physics isn't helping me here, but the best explanation I can see is that the secondary oscillation modes in the spokes are affected when the metal plate's primary vibration experiences the acceleration of motion caused by mousing.

That's probably off as an accounting of how things work (and I encourage feedback to set me straight here), but the mechanical structure is fundamentally a source of dual-axis acceleration vectors when married to some signal processing. In that vein, a custom IC designed by Cadence for Gyration handles what must be a mix of op amps and A/D converters in the GYRC10433. The Cadence part reads the pickups to get acceleration data and converts it to a serial digital format readable from the module, for motion control purposes. A 256-byte E2 PROM stores calibration constants for the module, probably to compensate for any manufacturing variables.

Drift-free operation

In a final, clever step, the four signal/power connections for the gyro module are delivered over a set of vibration-isolating coiled wires that suspend the gyro apparatus, eliminating drift and externally induced pointing errors.

Although the product targets PowerPoint presenters, the notion of gesture-based control extends into many other possible domains, among them the world of PC-based TV remotes. In fact, Gyration will be happy to have you spend about $100 on its GYR3101CA WindowsMedia-compatible Universal Remote, a gadget that takes the basic Gyrotransport technology in a decidedly more consumer- oriented direction.

It's noteworthy that the raw silicon area dedicated to the core free-space mousing functions of this product is dwarfed by the nearly 6-cm2 area needed for the 1 Gbyte of NAND memory. Al- though the storage capability of the Gyration product is intended to be an attractive secondary add-on function, the memory silicon real estate takes the podium by a wide margin.

It just goes to show that the big story in a product often comes from relatively small chips–and, as in the case of the gyro module, from something largely divorced from the world of silicon. n

David Carey is president of Portelligent (www.teardown.com), a CMP company. The Austin, Texas, group produces teardown reports and related industry research on wireless, mobile and personal electronics.

0 comments on “Under the Hood: Gyro sensor liberates mouse

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.