The MX700, like most premium mice these days, is an optical mouse. It shines an LED on the mousing surface, and then scans the reflected light. The mouse contains a lens, optical sensor and LED that shines through a light pipe onto the surface underneath the mouse, as shown in the figure supplied by Logitech.
The MX700 mechanism is fairly complex -- after all, you need power management, a DSP to handle image processing and some firmware to store that image processing software. The sensor is roughly 80% larger than the one used in past Logitech mice. Couple the large sensor size with a 4.7 megapixels per second processing rate, and you get a high "frame rate" -- the number of images processed by the DSP each second. Don't think of this as an $80 mouse -- think of it as an $80 image-processing computer.
The radio link operates at 125 samples per second -- roughly the same speed as the standard USB sampling rate. This accounts for the excellent 3D gaming performance, since this cordless mouse makes no compromises in sampling rate versus cordless mice. In addition, the resolution of the sensor has been doubled, from 400 dpi (dots per inch) in past mice to 800 dpi, making it ideal for large screen monitors. The light pipe and lens mechanism has also been upgraded, allowing for greater light passage, and reducing power consumption.
Speaking of power consumption, battery life has been improved -- but the issue is almost moot. Logitech supplies a pair of AA, 1.2V, 1700 mAh (milli-Amp hour), nickel-metal hydride rechargeable batteries, similar to those used in some digital cameras. The radio receiver has evolved from simply listening for radio signals to a base station with built-in battery charger. It's an elegant solution to the battery problem. If you like, you can even charge up a spare set, if you want the security blanket -- NiMH rechargeable batteries of this type cost under $5 per pair, and can take up to 1000 charges. You can use regular alkaline batteries as well, but the mouse won't properly detect when the batteries run out of juice. Only NiMH batteries are rechargeable. You can't recharge alkaline or NiCD batteries.
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