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Optical sensors boost mobile device efficiency

07 May 2008

Mobile devices that include an optical sensor from Osram can detect how they are being used and adapt accordingly to save battery power.

Osram Opto Semiconductors of Germany has unveiled two optical proximity sensors that it says will help to prolong the battery lifetime in devices such as mobile phones and digital cameras. The SFH7740 and SFH7741 use distance measurements to detect the operating status of mobile devices and adjust functions accordingly.

"The sensors will switch off the display and keypad when not needed, and also adjust the volume of the loudspeakers," Marion Reichl, public relations manager at Osram, told optics.org. "This results in less energy consumption and a longer battery lifetime. The amount of power the sensors will save depends upon the size of the display of the system in which they are used."

According to the company, the two sensors draw a current of around 50 µA and make use of integrated ambient light suppression, which mean that they operate reliably in all lighting conditions.

"The sensors use infrared emitters based on our thin-film technology and silicon photo-IC," explained Reichl. "The infrared light is reflected by the target and detected by the photo-IC, which in turn amplifies the signal and provides a digital output (on/off)."

The sensors are being targeted at mobile devices because they are SMT mountable and offer plug-and-play operation. "These sensors are small in size, cost efficient and consume low power," commented Reichl. "They could be used in other mobile appliances such as navigation systems, electronic handheld devices and in laptop displays."

The SFH7740 switch measures 3.7 x 3.7 x 1.0 mm and is sensitive over distances between 0.5 and 4 mm. Osram says that this switch could easily detect the position of the slider that reveals or hides a mobile phone's keypad. Depending on whether the slider is closed or open, the sensor could then switch the display lighting on or off. Its small size also means that it can be integrated into unusual designs with extremely low-profiles.

The SFH7741 has a working distance of 20 to 30 mm and is suitable for a range of applications. For example, when the switch detects that the phone is close to the caller's ear, it can turn off the backlight and adjust volumes. Similarly, in hands-free mode with the phone well away from the ear, the backlighting is switched on and the volume is increased.

When deployed in a digital camera, the SFH7741 will switch the screen off when a user is looking through the viewfinder instead of using the display to view the scene.

Osram says that both sensors have been integrated into commercial devices that will soon be available on the market.

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