Motion sensing technologies for mobile and gaming devices come in a variety of flavors, ranging from infrared sensors and inertial sensors to combo devices that integrate accelerometers and gyros. Thanks to the Nintendo Wii and Apple iPhone--and the limitless imagination of designers--motion sensing technologies are enabling a host of novel applications.
While the most widely used sensor is a simple infrared sensor (not based on microelectromechanical systems), MEMS accelerometers are getting a lot of attention for their use in the Wii and Apple iPhone, said Marlene Bourne, president and principal analyst at Bourne Research (Scottsdale, Ariz.).
Yet, there is still a lack of traction for MEMS sensors in mainstream applications.
Bourne believes technical innovation is no longer enough, nor is small size or low price. She said MEMS suppliers have demonstrated all three, but the most important question is still looming: Where's the value-add? "The early adopters will integrate MEMS sensors into their products, but they're not the mass market. And movement into the mainstream is what will ultimately drive the growth of MEMS sensors. But I don't see that happening anytime soon," said Bourne.
And there is still work to be done to leverage the technology's capabilities.
As an example, Sony's Sixaxis controller uses an inertial measurement unit (IMU), which combines an accelerometer with a gyro for six-degrees-of-freedom movement, but Bourne argues that since the controller is still a wing design, it does not take full advantage of MEMS sensing capabilities, as the Wii does.
There is also competition from lower-end phones using software like that from GestureTek, which replicates the interactive experience of a MEMS accelerometer. "This is easier, faster and less expensive to integrate into a cell phone than a sensor. So, just because a cell phone has screen orientation or interactive gaming, don't assume that a MEMS sensor is behind it," said Bourne.
Hillcrest Labs offers the Loop reference device--a pointer-based TV remote with two buttons and a scroll wheel--which uses its Freespace in-air inertial sensor technology for 3-D pointing. |
Still, designers are integrating more MEMS sensors into their mobile device designs and developing new and creative uses for them, despite the cost.
"The accelerometer will be the enabler for a lot more user interface functions that will be the standard in the future. With a certain motion you can achieve many types of detection within a few seconds, whether it's by shaking the device in one direction or another, or by tapping the device," said Michelle Kelsey, marketing manager for inertial sensors at Freescale Semiconductor Inc. (Austin, Texas).
Designers of portable devices are always trying to add more features without increasing size, so when it comes to sensors, they are looking for a number of things--fast response, low current consumption and low voltage operation--all in a tiny package.
In addition, designers are looking for higher sensitivity for motion applications, better temperature compensation offset, and more intelligence in the sensor, such as for threshold detection and click or pulse detection, Kelsey said.
With threshold detection, the user can program the threshold level to detect a tap or shock; with click or pulse detection, the user can program the threshold of the signal and timing of the signal to detect a single or double tap or when a user takes a step, allowing it to be used in pedometer applications, for example, she said.
Designers also want lower current consumption or a quick power-on response time, in order to power-cycle the device to achieve the targeted current consumption, as well as a sleep-mode option, to turn off the accelerometer when motion detection is needed, said Kelsey.
One sleep-mode example is turning off the backlight of a cell phone when it's lying on a table, and turning it back on when motion is detected.
Small is a big deal
Some of the latest triple-axis accelerometers are ultrasmall for consumer electronics products and suitable for applications such as gaming, hard-disk drive protection and security. Some feature quick power-up, zero-g detect for free-fall protection and a self-test function.
STMicroelectronics (Geneva) introduced a new generation of "nano" three-axis linear accelerometers late last year. The LIS331 family of low-power MEMS sensors provides embedded smart features for miniaturized motion sensing solutions in consumer and industrial applications. These include motion user interfaces in mobile and gaming devices, free-fall detection for hard-disk data protection, and even vibration monitoring and compensation in white goods.