Optical Touch Switch Makes Mobile Devices More User-Friendly

OSRAM Opto Semiconductors' two new SMT proximity sensors (SFH7740 and SFH7741) use distance measurements to detect a mobile device's operating status without physical contact to the sensor itself. This technology allows for the automatic shut-off of displays and keypads when no longer needed, improving performance and efficiency of products such as cell phones and digital cameras. The proximity sensors can also be used to adjust the volume of the device’s speakers.

The SFH7740 proximity sensor with optical touch switch measures just 3.7 x 3.7 x 1.0 mm and reacts to distances between 0.5 and 4.0 mm. These compact dimensions allow it to be unobtrusively integrated into unusual designs, such as extremely low-profile devices. For example, it is small enough to fit in slider phones where it can detect the position of the slider that reveals or hides the keypad. Depending on whether the slider is closed or open, the SFH7740 switches the display lighting off or on. The OSRAM sensor is an ideal alternative to Hall sensors as it is insensitive to electromagnetic interference and does not produce any electromagnetic interference itself.

OSRAM’s other new proximity sensor – model number SFH7741 – reacts at a typical working distance of 20mm and is suitable for a wide range of applications. For example it can detect when the phone is moved close to the ear, taking the display and the keypad out of sight of the user. The backlighting is then switched off and the volume adjusted. In hands-free mode with the phone well away from the ear, the backlighting can be switched on and the volume adjusted accordingly. The sensor can also help save energy in digital cameras, switching off the display lighting whenever users holds the camera up to their eyes and use the viewfinder instead of the screen.

The two SMT sensors draw a current of only 50 µA (approx.). They make use of integrated ambient light suppression and therefore operate reliably in all lighting conditions. Building on OSRAM’s line of ambient light sensors and orientation sensors, these two new SMT components are further evidence of the company’s expertise in sensor technology for mobile devices.

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