How do gyro sensors make the mouse so free?

At the suggestion of Jack Shandle, editor of Wireless DesignLine, we recently took a look at a gyro-based mouse. The ProGo Gyrotransport, made by Gyration, is a $150 device (which includes the Free Space mouse and a 1GB flash drive in a separate USB transceiver adapter that plugs into the host computer). For those unfamiliar with the subject, it's a simple, free-space motion and gesture-based positioning and control system. Wave the mouse across an imaginary plane, and the onscreen cursor follows, allowing you to circle links and click buttons. This is handy when you're giving a presentation or away from your desk.

I have to admit that I had a little trouble at first: I was about to call support when I couldn't get two buttons to work at once. But then I found the instructions clearly printed on a thin sheet of paper around the AAA batteries that power the mouse. This could be a design oversight or a user oversight, but once that was fixed, the rest was easy.

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 a MT29F8G08FABA 1GB NAND package made by Micron Technology, which stacks four 256MB SLC NAND chips in a TSOP package, which is the icing on the cake for this already very handy little mouse. To enable the memory to function as a flash drive, a Cypress CY7C68033 USB controller handles the USB and memory interfaces.

Connecting the controller and the memory is a Cypress CYWUSB6953 MCU, which creates half of the 2.4GHz wireless link needed to communicate with the air mouse.

The mouse is controlled by a TI mixed-signal MCU, the MSP430F1232, which has 8KB and 256KB of flash memory and 256B of RAM.

Next to TI's DC/DC boost converter, there's a Cypress CYWUSB6934 2.4GHz direct-sequence spread spectrum (DSSS) wireless SoC that 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 majority-owned by Movea, a spinoff of French Thomson, which still owns a small stake in the company.

The MG1104 is a far cry from the sensors I'd expect to see in today's age of silicon MEMS accelerometers. It's huge. The module, which is the size of a large candy bar (about 14mm on a side), has a lot of semiconductor material inside, but it only serves to assist the gyro sensor itself. The operation of a gyroscope is based on some basic physics principles of the Coriolis effect.

I hesitate to use the word "basic" because I have a hard time understanding how the physical structure of a gyroscope applies this principle. The key point seems to be that the Coriolis effect can derive horizontal and vertical speeds from the rotational speed and oscillations of the gyroscope disk as it moves.

The sensor is an etched metal disc that forms a complex network of driven central points for the finger. At first glance, it looks a lot like the old sleeves used with 45rpm vinyl records, which rotate on a standard LP spindle (I know I'm a bit outdated). The disc is coupled to a drive coil that creates a basic oscillation, and the individual spokes appear to be monitoring points for another more complex oscillation mode. I'm as clueless as 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 oscillation of the disc creates a search for acceleration.

Maybe the actual working principle is a little different from the above description (I sincerely hope that readers will correct me), but this mechanical structure is actually a vector source of dual-axis acceleration when combined with some signal processing. So it seems that this custom IC designed by Cadence for Gyration controls both the op amps and the ADC in the GYRC10433. The Cadence device reads the detection signal to obtain acceleration data, and then converts it into a serial digital format readable by the module for motion control. The 256B EEPROM stores calibration constants for the module, which can be used to compensate for any manufacturing variations.

Drift-free operation

Finally, in a clever step, four signal/power connections are provided to the gyro module via a set of oscillating isolation coils that suspend the gyro, eliminating drift and induced positioning errors.

Although the product was designed for PowerPoint presenters, the concept of gesture-based control has been extended to many other areas, including PC-based TV remote controls. In fact, Gyration would be very happy if it could get you to spend about $100 on a Windows Media-compatible GY3101A universal remote control. This consumer-oriented gadget uses basic Gyrotransport technology.

It is worth mentioning that the raw silicon area dedicated to the product's Free Space core functions is nearly 6cm2 less than the area required for 1GB of NAND memory. While the storage function of the Gyration product is an additional feature to enhance its appeal, the actual silicon area of ​​the memory is highly debatable. The above teardown

analysis only shows that the power of a product often comes from relatively small chips, and as in the case of the gyro module, the main function of the product comes from the part that has little to do with the silicon.