Tear Down: High-end mouse goes where no mouse has gone - Embedded.com

Tear Down: High-end mouse goes where no mouse has gone

A new set of innovations that were designed globally make this peripheral more useful than competitive products.

On the surface, it may look like any other mouse. But once you really understand all the engineering that went into Logitech's MX Revolution mouse, you can better appreciate the level of performance that it offers. I was skeptical myself, thinking, “How hard is it to design a mouse?”

Aside from the hand-pleasing contours that are designed into the mouse, there are two features that really caught my eye (and fingers). First, the scroll wheel works differently than any scroll wheel I've used before. It can be used either with detents (the clicks you feel while scrolling) or free-spinning (hence, the name “Revolution”). How you get from one mode to the other was the clincher for me. Simply press down on the wheel and it switches between modes. In addition, if you're in “click” mode and you spin the wheel quickly, i.e., to scroll far down in a document, the mouse senses this action and automatically switches modes.

The second feature also relates to scroll wheel, but it's got to do with the software design. When you switch between applications, the mouse knows which application is the active one and sets the mouse operations accordingly. For example, if you're working in Internet Explorer, the wheel spins freely, to simplify scrolling. But if you're working in Word, it switches to click mode for more precise pointing. The software lets you override these settings, but most popular applications offer a default setting.

The MX Revolution design team sat down some time in 2004 to commence the project. Actually, there were multiple design teams around the world working concurrently on this project, each tasked to design one of the mouse's subsystems. This includes the mechanical design (done in Ireland), the electrical design, the firmware (done in Switzerland), the tooling (in Taiwan), and the software (written in California). The intent was to replace the company's MX 1000 product. Logitech typically rolls a new mouse design about every two years.

Desktop and mobile versions
There are two versions of the Revolution, one for the desktop and one for the road. The mobile solution, which contains a completely different printed circuit board, runs from a AA battery rather than a rechargeable cell. It also uses a manual switch on the battery to toggle between the scroll wheel's free-flowing and detent modes.

Mass production will soon transfer from Taiwan to China, where Logitech has a manufacturing facility. The company claims that it must produce one mouse every 10 seconds to meet customer demand.

“Shortly after launch, we look at our products and ask what opportunities are still out there and what do we need to do to maintain our leadership position,” says Erik Charlton, senior global product manager at Logitech. “We provide a lot innovation at the high end, so the challenge was to not simply innovate for innovation's sake, but find the real value. A lot of our previous innovations had become mature, like the use of high-speed USB, long battery life, laser sensors, etc., so we needed some new innovations.”

The European touch
Logitech enlisted the help of Peter Sheehan, an industrial designer located in Ireland. Such an expert was required because comfort is a critical factor in a mouse. If it's not comfortable, it doesn't matter what else you've done in the design. That group hooked up with the Logitech's mechanical engineering team, led by senior manager Denis O'Keefe, also based in Ireland.

“When you look at a 24-month design cycle, there's really not that much time actually spent designing,” claims O'Keefe. “We started the tooling at the end of November 2005, which is a little earlier than usual. We got lucky on this design because we all came to agreement pretty quickly on what we wanted to accomplish.”

The scroll wheel (as well as the side thumb control) was very different from anything that had been done in a mouse before (see Figure 1). Since the scroll wheel first came into play around 2001, the only real change has been the tilt feature. The side thumb control lets the user quickly toggle between multiple applications.

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This wheel is an integration of many different technologies in a very small space. Even though there's limited power, a certain amount of energy was needed. The actual implementation is handled with an electric motor. There's a little arm that creates the ratchets and a cam on the motor. When you remove the motor, it removes the ratchets. The team looked at electro-magnetic solutions, but ruled them out because they need constant power.

One potential problem was that as battery capacity and voltage gets lower, performance could be affected. But the designers embedded a low-dropout regulator (LDO) to stabilize the voltage that's seen by the motor. Hence, the motor always sees the same 3 V.

Steel ball on a rubber pillow
To achieve a high-quality mechanical click, a steel ball is used to contact the wheel (see Figure 2). The steel ball is spring loaded, sitting on a rubber pillow. The pillow takes out the high-frequency sounds when the wheel is spinning at a high rate.

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The wheel itself is made from brass because it's a high-density material that's very suitable for high-speed machining. The wheel is chrome-plated for cosmetic reasons. Finally, a rubber grip is added for better contact.

The team had to develop special software to measure the wheel's speed. They claim the wheel can reach 3,000 RPM, whereas competitive products only get up to about 1,500 RPM. And it'll spin for about seven seconds.

“We felt that the scrolling experience hasn't really changed or been improved dramatically, but the users' needs have changed, such as documents are getting longer,” says Charlton. “So we look at both precision and hyper-fast scrolling. Ultimately, we decided we couldn't get too far from a traditional scroll wheel, because that's what people are familiar with.”

Acceptable battery life on one charge for such a product is now above five days. The MX Revolution goes for at least eight days, using a Li-Ion battery. It can fast charge to about 75% capacity in about 60 minutes. The mouse's laser comes from Avago.

The plastics are produced using a gas injection process. Nitrogen is injected into the part to produce its shape. The front is painted with a semi-gloss lacquer. Hence, you can't see the LEDs (used to indicate remaining battery capacity) unless they are lit. The result is a sleek, clean design. Test systems had to be developed to check the transparency of the plastic to ensure that enough light from the LEDs came through.

Teflon of a different color
Another aspect that end users may take for granted is how the mouse slides on the desk. According to Logitech's Charlton, this was a non-trivial task. “The way you dampen the sound is important. The perception is that if it sounds gritty, it's not a quality product.”

Under the mouse's feet is a layer of foam to dampen the sound, lined by Teflon. Charlton claims that they spent about two man-months trying to get black Teflon from their sources.

The MX Revolution's RF communications are handled with proprietary 2.4 GHz technology. Bluetooth was avoided because of power and cost issues. The latency issue that appears on competitive products mostly in sleep and hibernation modes was resolved by radically increasing the mouse's report rate. Full-speed USB 1.1 is employed, which lets the mouse make quick movements.

The cradle that ships with the MX Revolution is a derivative of what was used on previous generations. The biggest difference is that it employs an exaggerated alignment feature and removes some of the excess plastic. The molding makes it more obvious to the user that the mouse is seated properly. The green LEDs on the mouse let the user know the charging state.

Also, the docking cradle isn't used to handle the RF connection as is the case on previous generations. That allows the cradle to have just one wire, for the power, ultimately reducing desktop clutter.

Richard Nass is editor in chief of Embedded Systems Design magazine. You can reach him at .

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