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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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SFH4645 датащи(PDF) 9 Page - OSRAM GmbH |
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SFH4645 датащи(HTML) 9 Page - OSRAM GmbH |
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9 / 14 page  August 13, 2010 page 9 of 14 In some enhanced applications it might be worth to consider an external lens in front of the emitter to create a slim IR curtain only above the screen. This might also be advantageous concerning power saving issues, as it allows reducing the IRED drive current. Exemplary Calculation The following simple calculation illustrates above relations in a matrix-type application. The emitter is a SFH4650-V (90 mW/sr at 100 mA), the detector a phototransistor SFH309FA-4. The detector is located axially on the opposite screen side, inside the bezel. Unfavorable ambient IR light conditions incident on the detector are assumed to be an equivalent irradiance of 25 µW/cm2 (e.g. shadowing the detector behind the bezel and bright incandescent light bulbs near the screen). To achieve a signal-to-noise ratio (SNR) of at least 6 at the detector, an E e = 0.15 mW/cm2 is required (for a comfortable I PCE ≈ 0.45 mA). Using I e = Ee·r 2 yields for a 7- inch screen (9.1 cm x 15.5 cm) a necessary radiant intensity of 12 mW/sr (vertically emitting) and 36 mW/sr (horizontally). According to the data sheet a drive current IF of 13 mA resp. 40 mA is required. Increasing the screen size from 7-inch to 14- inch and keeping the SNR stable results in an increase in the required radiant intensity by a factor of four (roughly quadrupling the operating current – in this particular case it is necessary to operate under pulsed conditions). In the above 7-inch screen example, the crosstalk from a neighboring IRED (spaced 2 cm apart) is around 25 % of the signal for the vertical grid (the angular arrangement causes the radiation characteristics to drop to 60 % resp. the detector’s sensitivity to 40 %). This value rises to over 80 % if the screen size doubles. This demonstrates the importance of sequentially pulsed operation of larger matrix-based touchscreens. As an alternative, a proper mechanical design which shadows the detectors from neighboring light, especially with increasing screen sizes resp. resolution is advised. More focused emitter / detector pairs are recommended anyway to avoid x-y crosstalk and reduce interference from ambient light. 4.5 Power Supply Considerations If the electrical power supply is limited (e.g. battery powered applications or USB connected touchscreens with a max. 500 mA supply) it is recommended to operate the IREDs in pulsed mode. Synchronization with the detector is advised for better signal- to-noise ratio and lower overall power consumption. Please note that in pulsed operation the IREDs can be operated at higher drive currents resulting in higher optical peak powers compared to continuous operation. Please refer to the data sheet for details. 5. Product Selection Guide Tab. 2 - 7 present a short product selection guide which highlights products and product families of OSRAM which are suitable for IR touchscreen applications. For many package variations top- or side-emitting options are available. Please note that this guide provides just a general overview. For more detailed information and the latest products and updates please visit www.osram-os.com. 6. Literature [1] OSRAM-OS: http://www.osram-os.com. [2] G. Kaindl: Exploring multi-touch interaction. VDM Verlag Dr. Müller, 2010. [3] Interactive Displays Conference: http://www.int-displays.com. [4] LLFY-Network: http://www.ledlightforyou.com |
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