Some confusion comes from the fact that the Wii Motion Control system uses multiple MEMS units. It is a surprisingly complex and sophisticated device. The following is information excerpted from the well done Wikipedia article.
The Wiimote and Sensor Bar
The Wii Remote has the ability to sense acceleration along three axes through the use of an ADXL330 accelerometer. The Wii Remote also features a PixArt optical sensor, allowing it to determine where the Wii Remote is pointing.
Unlike a light gun that senses light from a television screen, the Wii Remote senses light from the console's Sensor Bar (model number RVL-014), which allows consistent usage regardless of a television's type or size. The Sensor Bar is about 20 cm (8 in) long and features ten infrared LEDs, five at each end of the bar. The LEDs farthest away from the center are pointed slightly away from the center, the LEDs closest to the center are pointed slightly inwards, while the rest are pointed straight forward.
Because the Sensor Bar also allows the Wii Remote to calculate the distance between the Wii Remote and the Sensor Bar,the Wii Remote can also control slow forward-backward motion of an object in a 3-dimensional game. Rapid forward-backward motion, such as punching in a boxing game, is controlled by the acceleration sensors. Using these acceleration sensors (acting as tilt sensors), the Wii Remote can also control rotation of a cursor or other objects.
The Wii Remote contains a 16 KiB EEPROM chip from which a section of 6 kilobytes can be freely read and written by the host. Part of this memory is available to store up to 10 Mii avatars, which can be transported for use with another Wii console. At least 4000 bytes are available and unused before the Mii data.
Nunchuk
The Nunchuk (model number RVL-004) is the first controller attachment Nintendo revealed for the Wii Remote at the 2005 Tokyo Game Show. It connects to the Wii Remote via a cord that is about 3.5 to 4 feet (1 ~ 1.2 m) long. Its appearance when attached resembles the nunchaku, hence the name. It features an analog stick similar to the one found on the Nintendo GameCube controller and two trigger buttons (a last minute modification changed the two triggers to one trigger and a "C" button, as described below). It works in tandem with the main controller in many games. Like the Wii Remote, the Nunchuk also provides a three-axis accelerometer for motion-sensing and tilting, but without a speaker, a rumble function, or a pointer function. The Nunchuk's accelerometer is an STMicroelectronics LIS3L02AL.
Wii MotionPlus
The Wii MotionPlus is an expansion device that allows the Wii Remote to more accurately capture complex motion. According to Nintendo, the sensor in the device supplements the accelerometer and Sensor Bar capabilities of the Wii Remote to enable actions to be rendered identically on the screen in real time. The Wii MotionPlus was announced by Nintendo in a press release on July 14, 2008, and revealed the next day at a press conference at the E3 Media & Business Summit. It will be bundled with the sports game collection Wii Sports Resort, which is scheduled for release in Spring 2009 The device will also be available for purchase separately, Red Steel 2, The Conduit, and an EA Sports-branded tennis video game by EA Canada were announced as Wii MotionPlus-compatible titles.
The device incorporates a dual-axis "tuning fork" angular rate sensor, which can determine rotational motion. The information captured by the angular rate sensor can then be used to distinguish true linear motion from the accelerometer readings. This allows for the capture of more complex movements than possible with the Wii Remote alone.
The Wii MotionPlus was developed by Nintendo in collaboration with game development tool company AiLive. The sensor used is an InvenSense IDG-600; designed in accordance to Nintendo's specification; with a high dynamic range, high mechanical shock tolerance, high temperature and humidity resistance, and small physical size.
In an interview with video game trade journal GameDaily BIZ, Satoru Iwata stated that the Wii MotionPlus was conceived soon after the completion of the initial Wii Remote design, to address developer demand for more capable motion sensing, but was only announced after the sensors could be purchased in sufficient volume at a reasonable price.
And you thought "Waggling" was easy.
