Reflective Optical Switch: SFH774X
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An Introduction to Reflective Optical Switch: SFH774X
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Reflective Optical Switch: SFH774X
- 6. Block Diagram of SFH 7740/41
- 7. Start-up Sequence of SFH 7740 Timing diagram
- 8. Design and Operating Principle of SFH7741 SFH 7741 output as a function of the photocurrent Ip, illustrating the decision circuit hysteresis.
- 10. Application Circuit SFH 7741 proximity sensing set-up
- 11. SFH 7740 Application Circuit Target reflectivity measurement setup. SFH 7740 application schematic diagram,
Editor's Notes
- Welcome to the training module on Osram Reflective Optical Switch: SFH774X
- This training module will introduce the Reflective Optical Switch: SFH774X].
- 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. This device was conceived to detect the position of mechanical parts. The contact-less SMT sensors SFH7740 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 SFH 7741 is a very small reflective optical sensor for short distances with digital output. With dimensions of only 3.7x3.7x1mm3, and surface-mount solder contacts, the device may be integrated in applications where reflective sensors have previously not been considered, This device was conceived to operate as a short- to medium-distance proximity sensor. The typical operating range is around 30 mm for a diffusely reflecting target with high reflection coefficient. 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. it detects when the phone is moved close to the ear, taking the display and the keypad out of sight of the user.
- This page gives features and applications of the SFH7743 device, its Typical Working distance with external emitter SFH 4650: 40mm, it has Opto hybrid with Schmitt trigger output, open drain it is Extremely low power consumption with Very small SMD package, it has High ambient light suppression.
- The SFH7740 and SFH7741 sensors are active devices, unlike the Hall Effect sensors mentioned in the company's press release. 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 contributes to low power 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.
- 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. 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. optical response, is rated from 730 nm to 1080 nm. When the supply voltage reaches Vdd (start) , the sensor output stays low for 60ms < t_start <120ms. Subsequently approx. every 90ms the reflected signal is measured and the output is set accordingly
- The part consists of an infrared light emitting diode (LED) with a wavelength of 850nm, a phototransistor, and an ASIC. A block schematic diagram is shown here. For low current consumption (45µA average at Vdd=3V, Rprog=470Ω) the ASIC performs a measurement every 90ms and the result is latched at the output and held until the next measurement result is present. When a measurement is performed, the emitter is driven with current If for 44µs. The phototransistor current IP is measured twice, The difference between the two measurements is compared with an internal threshold setting, and the output is set to the appropriate digital level
- This page shows block diagram of SFH7743. The external emitter can be driven directly with 10 mA to 60 mA in pulsed mode; this means, that any series resistance on the V dd line causes a voltage drop at the power pin. The IR emitter pulse is a high, short load for the power supply
- In any reflective optical sensor, the detector receives light not only from the desired target. Ambient light, as well as reflections from other objects such as frames or covers, contribute to the detector signal. In most applications the sensor may be placed behind an IR transparent window. The detector signal comprises signal portions from light reflected by the detected object, ambient light, crosstalk due to cover window, frames or other objects in the vicinity.
- The part consists of an invisible infrared light emitting diode (LED) with a wavelength of 850nm, a phototransistor, and an ASIC. Target position is detected by measuring the amount of light reflected from different areas the ASIC performs a measurement every 90ms and the result is latched at the output. The device is designed to provide an operating range of approximately 0.6 to 1.4mm, assuming the preset emitter current (10 mA) and a target that reflects diffusely with a reflection coefficient of 90%
- Thank you for taking the time to view this presentation on “ the SFH7746X” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link right beside the play button on the TechCast portal, or simply call our sales hotline. For more technical information you may either visit the [OSRAM] site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit element14 e-community to post your questions.