Follow-up Story: Tearing down the Wii --- 'Sensor Bar' Features No Sensor

Nov 28, 2006
Nikkei Electronics
When screws were removed, sensor bar's inside became visible. Few components form simple structure.
When screws were removed, sensor bar's inside became visible. Few components form simple structure.
[Click to enlarge image]
Five infrared LEDs are set at sensor bar's both side edges. Gray cable extending from right bottom and soldered with substrate comes from Wii main unit. White flat cable with red line reaches LED substrate on the other side.
Five infrared LEDs are set at sensor bar's both side edges. Gray cable extending from right bottom and soldered with substrate comes from Wii main unit. White flat cable with red line reaches LED substrate on the other side.
[Click to enlarge image]
Pixart Imaging's CMOS image sensor attached at Wii Remote's top end
Pixart Imaging's CMOS image sensor attached at Wii Remote's top end
[Click to enlarge image]

One of the major features of Nintendo Co., Ltd.'s new "Wii" game console is the innovative "Wii Remote" controller with motion sensor capability introduced. As we reported in our review on tearing-down of the Wii Remote (related story on Tech-On!), it features a built-in three-axial acceleration sensor, which detects shaking, tipping and other motions of the controller and provides these data for game operation.

The Wii Remote is also able to estimate positional relation between itself and the TV screen using infrared ray. This capability can be used not only for gaming but also as a pointer, which manipulates a GUI by pointing the screen with the Wii Remote. For this purpose, the Wii requires users to set a thin, long device called a "sensor bar" above or below the TV screen.

At the top of the Wii Remote, a component, which is supposed to be a CMOS sensor, is mounted, but the mechanism how the sensor bar works with the Wii Remote is unknown. So we tore down the sensor bar. The top cover of the sensor bar was also fixed with unique Y-shaped head screws as the Wii main unit was. As we removed these screws, the sensor bar's astonishingly simple structure became evident.

In contradiction to its name, there was no kind of sensors inside the sensor bar. The bar was only embedded with five infrared LEDs on each side edge, inside the black acryl plastic cover. These five LEDs are connected in series and supplied with about 7.3 V direct current voltage from the Wii main unit. It is not that we examined it closely; but there seemed to be no modulation in light, with the LEDs simply lit all the time.

Let's infer the Wii Remote's mechanism based on these facts. When the Wii Remote faces the TV screen, the light points at both sides of the sensor bar will be captured by the controller's image sensor. Then the Wii Remote's direction, distance and other situations in comparison with the TV screen can be estimated to some extent based on these two light points' positional relation and interval. Combining these data and information on the controller's posture or tilt acquired through its three-axial acceleration sensor, an area on the screen, which the user is pointing with the controller, can be determined.

We could not find any microprocessor to perform such processing on the Wii Remote's substrates. Therefore, it is highly probable that information acquired through the image, acceleration and other sensors is sent to the Wii main unit via Bluetooth and then the main unit performs most processing related to determination of the pointer's whereabouts.

Pixart Imaging Inc. of Taiwan supplies the Wii Remote's CMOS image sensor. This was made known when the company announced so on May 12, 2006 (press release). Pixart Imaging is a specialized manufacturer of CMOS image sensors, whose main products are relatively low resolution image sensors used for optical mice and embedded devices.

In light of Pixart Imaging's product lineup, the Wii Remote's CMOS image sensor, too, is assuemed to have only moderate resolution. However, considering that the Wii Remote is required to provide snappy operation touch, Nintendo must have chosen a relatively high-responsive product. In addition, given a limited Bluetooth bandwidth allotted for data transmission, the CMOS image sensor may have been embedded with a circuit, which gives preprocessing to images to reduce their data volume.