A recent teardown of a gyroscope-based mouse, the ProGoGyrotransport, made by Gyration Corporation and costing $150 (includes a FreeSpace-enabled mouse and a separate USB transceiver adapter that attaches to the host computer) 1GB flash drive). For those unfamiliar with this type of product, it’s just an easy-to-use free-space movement and gesture-based positioning and control system. Swipe your mouse on the imaginary plane and the on-screen cursor will follow, and you can circle links and click buttons. These are all handy when you’re giving a speech or leaving the table.
I have to admit that I had a little trouble at first: I was about to make a support call because I couldn’t operate both buttons at the same time. But then I found instructions clearly printed on a thin wrapper on the AAA battery that powers the mouse. This may be due to a design omission or user negligence, but after solving this small problem, the rest of the operation is simple.
1GB flash drive
A small USB transceiver on the PC side communicates with the mouse over a 2.4GHz link, while 1GB of NAND memory is built in. Among the parts to be analyzed is an MT29F8G08FABA1GBNAND package made by Micron Technologies, which stacks four 256MB SLCNAND chips in a TSOP package, which is the icing on the cake for this already very convenient little mouse. In order for the memory to function as a flash drive, the USB and memory interfaces are handled by Cypress’s CY7C68033USB controller.
Connecting the controller and memory is Cypress’s CYWUSB6953MCU, which creates half of the 2.4GHz wireless link needed to communicate with the air mouse.
The mouse is controlled by TI’s mixed-signal MCUMSP430F1232, which has built-in 8KB and 256KB of flash memory and 256B of RAM.
Next to TI’s DC/DC boost converter is a Cypress CYWUSB6934 2.4GHz direct sequence spread spectrum (DSSS) wireless SoC, which creates the other half of the 2.4GHz wireless link.
While Cypress’s wireless USB devices are always impressive in the chip world, there’s another equally intriguing device in the mouse, the MG1104 gyroscope module from Gyration. Gyration is controlled by Movea, which is a spin-off from France’s Thomson, and Thomson still owns a small amount of the company’s shares.
The MG1104 is very different from the sensors I’d expect to see in today’s era of silicon MEMS accelerometers, and it’s exceptionally large. The size of the module is close to that of a large piece of candy (about 14mm side length), and there are many semiconductor materials inside, but only for the auxiliary function of the gyro sensor itself. The operation of the gyroscope is based on some basic principles of physics of the Coriolis effect.
I’m very reluctant to use the word “fundamentals” because I have a hard time understanding how the physics of gyroscopes applies this principle. The key point seems to be that the Coriolis effect is able to derive horizontal and vertical velocities from the rotational speed and the oscillations of the gyro disk as it moves.
The sensor is an etched sheet of metal that forms an intricate network of driven central points for the finger. At first glance, it looks very much like an old solid case used with 45rpm vinyl records, capable of spinning on a standard LP shaft (I know I’m a little out of date). This sheet of metal is coupled to a drive coil that forms the fundamental oscillation, while the individual spokes appear to be monitoring points for another, more complex oscillation mode. I don’t know much about this like a poor college freshman, but the best explanation I can give is that the second oscillation mode of the spokes is affected when the initial oscillations of the metal flakes form a search acceleration.
Maybe the actual working principle is a bit different from the above description (I sincerely hope that readers will correct me), but this mechanism is actually a vector source of two-axis acceleration when combined with some signal processing. It appears that this custom IC designed by Cadence for Gyration controls both the op amp and ADC in the GYRC10433. Cadence’s device reads the sense signal to obtain acceleration data, which is then converted into a serial digital format readable by the module for motion control. The 256B’s EEPROM stores calibration constants for the module, which can be used to compensate for any manufacturing differences.
Drift free operation
Finally, a clever step is to provide 4 signal/power connections to the gyro module via a set of oscillating isolation coils suspending the gyro, thus eliminating drift and induced positioning errors.
While the product is designed for presenters using PowerPoint, the gesture-based control concept has expanded to many other areas, including PC-based TV remotes. In fact, Gyration would be more than happy to spend about $100 on a Windows Media-compatible GY3101A universal remote. This gadget for consumer applications uses basic Gyrotransport technology.
It is worth mentioning that the raw silicon area dedicated to the FreeSpace core function of this product is nearly 6cm2 less than that required for 1GB of NAND memory. While the memory capabilities of Gyration’s products are an add-on to enhance the appeal, the actual silicon area of the memory is highly debatable.
The above dismantling analysis just shows that the powerful functions of products often come from relatively small chips, just like in the case of gyro modules, the main functions of products come from parts that have little to do with silicon chips.