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That moving feeling


There is a difference between fashion and style. Fashion is passing and while you think it’s the way of the future you soon find out that it’s old and dull. Style is intrinsic, it’s always there. If ringtone composers, biorhythm and horoscope programs  on phones were a fashion, music is style.

Every time you come across an interesting new technology the vendor says “it only costs a few cents, one day all phones will have it”. That’s true of fingerprint readers, push to talk, noise cancelling second microphones, GPS and accelerometers. The truth is that phones are becoming more diverse and the number of features which roll across all of them are becoming fewer and fewer. Even front-facing video cameras which were seen as mandatory on 3G phones are now less common.

One technology, which if not ubiquitous, that does seem to be becoming more common is motion sensing. Let’s get the Wii word out of the way early: It’s made motion cool. But phones have been a bit more prosaic.  It’s typically been used to distinguish between landscape and portrait views of a screen.

The Samsung SCH-310 lets you write a number in the air but how about using the motion sensor to see if the phone has had a sudden impact? Is the user an old person who might have fallen over or down the stairs? How about using it to affect the polling rate – if a phone hasn’t moved does it need to poll the cell to say it’s still in the same place?  Think of the power saving if a phone that’s left on the bedside table over night only polled a quarter as often. It would make a massive difference to standby time.

The accelerometer system measures the g-force on the phone. If you hold a phone steady it will always read 1g pointing straight down. So if you tilt the phone you can measure that. They typically use three cantilever beams as MEMS, and are very simple to work with. It’s also possible to detect an impact on the screen to look for a double click. The software to read the accelerometer needs the programmer to write a low-pass filter to eliminate the effects of gravity.

The typical cost of the three axis accelerometer hardware is $1.61. But there is a way of doing it for free.  A lot of phones in Japan use the camera for motion sensing. This technology is usually supplied by a company called GestureTek and the games for it include boxing and darts where the player puts the phone on the table and waves their hands in front of the camera. Games like fishing and bowling use a swing of the phone while the camera reads the world flying by. Sony Ericsson has built this into the F305.  GestureTek can do optical motion with Brew, Symbian S60 and Windows Mobile as well as JSR 256 and NTT DoCoMo DoJa. This includes gestures for shake, rock and roll.

You don’t need a great camera, indeed it’s best of the resolution can be reduced and the frame rate increased. It works best with the camera at lowest resolution of  160 x 120 and needs 7.5fps, 15fps is ideal. The software doesn’t use colour it  only looks at the image luminance.

Using the camera has a certain elegance. You can build motions into gestures and provide a toll that can record gestures like a bowling swing. Record several user string each defined gestures. The camera can be used to measure distance – which an accelerometer cannot –  but it’s relative, not suitable for dead reckoning. The power consumption of the of the camera is similar to the screen but running the camera at a lower resolution makes a significant difference. Unfortunately this is not possible with all hardware.

But unlike many of the things set to become “standard” in phones which never will, a camera pretty much has, so perhaps motion sensing will too. Perhaps it has been elevated from fashion to style.

Cat Keynes publishes her thoughts on the mobile phone industry every Sunday at www.catkeynes.com you can read the column  the previous Friday by subscribing here. Follow me on Twitter here.


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