|
 |
rlcZONE Products for the week of May 5, 2008
Osram Opto Semiconductors Says…
SFH7740/41: Contact Free SMT Optical Switches Help Sense Your Product Use
The two contact-less SMT sensors SFH7740 and SFH7741 from OSRAM Opto Semiconductors will enhance the convenience of mobile devices such as cell phones and digital cameras and also save on battery power. The sensors use distance measurements to detect the operating status of the mobile devices and switch the display and keypad off as soon as they are no longer needed. They also adjust the volume of the loudspeakers.
The SFH7740 switch measures just a few millimeters (3.7 x 3.7 x 1.0) and reacts to tiny distances between 0.5 and 4 mm. It is so small that it will even fit in slider phones where it detects the position of the slider that reveals or hides the keypad. Depending on whether the slider is closed or open it switches the display lighting off or on. The sensor is insensitive to electromagnetic interference and does not produce any electromagnetic interference itself. It is therefore an ideal alternative to the Hall sensors currently in use. Its compact dimensions mean that it can be unobtrusively integrated even in unusual designs, such as extremely low-profile devices.
The tiny SFH7741 optical proximity switch reacts at distances of 1.5 cm to around 5 cm and is suitable for a wide range of applications. For example it detects when the phone is moved close to the ear, taking the display and the keypad out of sight of the user. The backlighting is therefore switched off and the volume adjusted. In handsfree mode with the phone well away from the ear the backlighting is 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 for example.
The two SMT sensors only draw a current of around 50 uA. They make use of integrated ambient light suppression and therefore operate reliably in all lighting conditions. Following on from ambient light sensors and orientation sensors, these two new SMT components are further evidence of OSRAM's expertise in sensor technology for mobile devices.
EN-Genius Says…
If you've ever twirled an Apple iPhone by 90º, simply to delight in the way its display follows your wrist twist, you'll appreciate the role sensors play in nomadic electronics devices. It's clear that solid-state sensors are supplanting electromechanical devices frequently these days, as these contact-less surface-mount devices from the venerable firm of Osram attest.
The SFH7740 and SFH7741 sensors are, however, active devices, unlike the Hall Effect sensors mentioned in the company's press release. Osram’s EMI/RFI-resistant parts typically draw only about 45 µA, which is reasonable for devices designed into a battery-powered product. Hall devices require current-hungry conditioning circuits, too, after all.
As pulsed devices, reflected signals are measured internally every 90 ms, and the device output is then readjusted accordingly. LED on-time is a short 44 µs, with about 90 ms of off-time, which presumably contributes to low dissipation.
As 3-V opto-hybrids equipped with on-board Schmitt trigger outputs, these low-power devices provide open-drain FET output stages for driving external circuits. A programming resistor, a few power-supply line bypass caps, and a pull-up resistor for the output FET is all that’s required on the electrical front.
Not mentioned is that minimum and maximum sensor working distances can only be reached by using external light reflectors and absorbers. Keep in mind that will add to implementation real-estate requirements and product complexity.
The company's press statement, and its preliminary data sheet, indicate its SFH7740 sensors react over distances between 0.5 mm (0.020 inch) and 4 mm (0.160 inch). For their part, the SFH7741 devices can sense at distances from 1.5 cm (0.600 inch) to 5 cm (about 2 inch).
 The SFH7740 and SFH7741 emitters peak at 850 nm, and the sensor elements exhibit maximum sensitivity to light at 880 nm, however the internal phototransistors have a broader response than the emitters. Overall optical response, therefore, is rated from 730 nm to 1080 nm. As such, Osram claims its sensors will operate reliably under most ambient lighting situations.
Silent Company And Paper Tigers
Are these parts available? Perhaps not. A preliminary data sheet has been published to date, but repeated telephone requests to Osram’s main offices, as well as company distributors, result in unanswered calls. It looks like Osram is playing the old pre-announcement game. Even product manager Andreas Vogler doesn’t return calls.
That’s too bad, because Osram has been around for a long time. It was one of Europe's first vacuum tube manufacturers in the early days of radio, competing with the likes of de Forest and RCA. It also started out making incandescent light bulbs, and its present product portfolio includes high-power LEDs (the city of Banff in the middle of the Banff National Park at the foot of the Canadian Rocky Mountains, is using these LEDs to upgrade its street lighting).
The company now has three decades of experience with optoelectronic semiconductors, and holds more than 3000 patents. So, why doesn’t it answer requests for more technical information and typical pricing on these devices? In the United States, Osram Opto Semiconductors has a Silicon Valley office in Santa Clara, California. Maybe you can do better than I scaring up detailed information on these parts. Try reaching Osram at 888-446-7726.
|
|
|
|
|
