Optical mice supplanted roller-ball mice. So what happens when an upside-down optical mouse sensor is put in a mobile phone?
Stephen Shanklandprincipal writer
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LONDON--The same technology that exterminated the roller-ball computer mouse will claim another casualty soon: the four-way rocker switch that lets people point and click on countless mobile phones.
So asserts Jeff Raynor, principal technologist of ST Microelectronics' imaging division and a designer of the image sensors at the heart, or rather in the eyes, of optical mice. He spoke at the Image Sensors Europe conference here.
What will extinguish the rocker switch? What Raynor calls the "fingermouse"--a small, smooth pad you can sweep your finger over to direct a mouse pointer on a screen. Some newer BlackBerry phones sport the devices.
Fingermice use exactly the same image sensors as optical mice, but they're mounted upside-down, pointing upward toward a finger rather than downward toward a desk. The sensors take 400-pixel images, then recognize the movement of features in the photo sequence--desk irregularities or fingerprints, for example--to gauge motion.
Raynor's company makes silicon-chip image sensors for optical mice, so one shouldn't be surprised by his enthusiasm, but he is in a position to know what he's talking about.
Raynor holds 20 patents, with more applied for, and ST Microelectronics has sold more than 100 million image sensor chips for optical mice. And he expects the fingermouse market to be even bigger--"definitely."
That's because, of course, mobile phones sell by the millions. Even though touch screens are catching on in smartphones, there are plenty of lower-end models or products that use both a touch screen and some form of pointing navigation device.
ST Micro isn't the only player. Avago Technologies has already sold its sensors. Raynor won't say whether ST Micro has any fingermouse design wins yet, but he said he expects some this year.
The technology has its broadest application in mobile phones, but there are other areas it can be used: TVs, remote controls, music and video players, satellite navigation systems, smaller Netbooks, and cameras. Raynor showed off one prototype to run his presentation, a USB device with two sensors. They were buttons, too--one left and one right.
One nice feature of the fingermouse is that it doesn't require much force to move. Another is it can be operated with precision.
"You're using the part of your body best designed for your fine motor skills," Raynor said.
The system works with an infrared LED that illuminates the fingertip atop the sensor. A camera takes photos at a rate of up to 10,000 frames per second to gauge movement of the finger sliding across.
Don't expect fingermice to replace regular mice, though. For big screens on PCs and laptops, it's useful to have a pointing device that can be swept rapidly over a large distance, then slowed down for precise positioning at the end of the sweep. With a fingermouse, there simply isn't enough real estate for that.
Sensor orientation isn't the only thing that inverts with fingermice. So does one aspect of dominance.
"The difference between a phone and a PC mouse is that the mouse sits on a desk and goes to sleep. The PC mouse is a master," with a mouse jiggle waking the computer up from sleep.
But on a phone, the system must be designed so that fabric brushing against the sensor while it's in a pocket doesn't keep the system awake and consuming battery power. "The phone wakes the mouse up," he said.
Power consumption is important on mobile phones, but some of the challenges have been solved with battery-operated optical mice. ST Micro's sensors take photos at a rate of 10,000 frames per second during high-speed mouse motion, and slow to 4,000, 2,000, or 1,000 for slower motion. When the mouse idles, it slows gradually from 100 to 10 to 2 frames per second to check if it's been moved.
The optical mouse got its start, indirectly, in a $700 handheld Hewlett-Packard scanner called the Capshare that arrived in 1998. It was a dud in the marketplace, but the HP sensors that it used to gauge motion lived on in mice. The first product: the Microsoft IntelliMouse released in 1999.
ST Microelectronics' sensors arrived in Microsoft mice starting in 2001, Raynor said.
As fingermice are arriving, optical mice are changing, too. Raynor was cagey about details, though.
"Quite a few things will improve--the value to the customer, and features not obvious at the moment," Raynor said.