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Application of light sensor in rainwater detection
Application of light sensor in ambient light detection
Application of light sensor in temperature control
Application of optical sensor in tunnel detection
solution:
Valeo rain sensor
Ambient light sensor uses the visible wavelength of 380nm ~ 780nm to replicate the sensitivity of the human eye
Photodiodes play an important role in temperature control
Tunnel detection is controlled by a "look up" sensor and a "forward looking" sensor
Thirty years ago, the first cadmium sulfide photo resistor was used on passenger cars to automatically turn the headlights on and off by detecting ambient light. Today, mainstream technologies for detecting light have become silicon photodiodes and phototransistors, which has greatly expanded body electronics applications.
In most cases, photodiodes are used in automotive applications because the photocurrent and wavelength sensitivity of these devices are linear over the typical body temperature range of -40 ° C to +85 ° C. The direct current gain and dark current of the phototransistor have a higher temperature dependence than the photodiode. The advantage of a phototransistor over a photodiode is that the output current of the former is much higher than the latter when the amount of light is the same, so that amplification may not be necessary.
Rainwater detection
A Valeo rain sensor mounted on the windshield and part of the mirror unit. The sensor consists of an infrared emitting diode and a photodiode. The photodiode is used to detect the amount of emitted light reflected by the glass. The infrared light is emitted through the sensor device at a precise angle, reflected inside the windshield, and then returned to the photodiode. When it began to rain on the day, the raindrops fell on the windshield, and some of the light would refract, reducing the amount of light reflected back to the photodiode. As the amount of rainfall increases, the amount of light that is reflected back to the detector surface will decrease.
Eventually, the output current will drop below a defined threshold and the sensor will indicate "raining." With this input to the microcontroller, the sensor turns on the wiper and adjusts the speed of the wiper.
Ambient light detection
In body electronics applications, ambient light sensors are used to adjust the backlight intensity of the instrument panel, as well as the navigation system (GPS), temperature control, and LCD backlight intensity in the DVD screen. This is especially important for displays such as BMW's iDrive and Prius's Multi-Info. For example, when daylight becomes dim and dark, the dashboard backlight will be adjusted to varying degrees to achieve optimal visibility and reduce the glare that may be caused to the driver. The use of these sensors eliminates the annoying process of automatic brightness adjustment of the display when turning on the headlights during the day. The key function of the ambient light sensor is to use the sensitivity visible wavelengths of 380 nm to 780 nm to replicate the sensitivity of the human eye.
temperature control
Photodiodes play an important role in temperature control by determining the angle of daylight and adjusting the fan speed and temperature along with the thermistor. Determining the angle of daylight is the illumination function on the photodiode, where the peak illumination can be converted to daylight at the highest point. Photodiodes with integrated NTC thermistors are best suited for this type of application.
Tunnel detection
Tunnel detection requires the input of two sensors. The first sensor has a wider field of view "looking up" and a relatively long average moving time period that prevents the lights from turning on and off for extended periods of time. The second sensor has a narrower view of "looking forward" and a relatively short average moving time period. This allows the tunnel sensor to react quickly to sudden changes in daylight, turn on the headlights, and adjust the backlight brightness of the display as it enters the tunnel. The forward sensor eliminates the need to turn the lights on and off when entering the bridge or under the trees that cover the sky. In these cases, the sensor will still "see" the light in front.
When entering the tunnel, the tunnel sensor signal will drop and the wide field of view sensor signal will remain high; the headlights will turn on. When the tunnel is out, the tunnel sensor signal will be boosted and the wide field of view sensor signal will drop; the headlights will turn off. With different average moving time periods, the controller can make a clear distinction.
in conclusion
The use of light sensors, especially photodiodes and phototransistors, in body electronics applications increases the safety and convenience consumers demand. These features may currently only be used in high-end cars, but as is the case with automotive applications, these features will soon be applied to cars at all price points.
Jim Toal is Senior Product Marketing Manager for Vishay Optoelectronics Sensors and IrDA Division. Vishay is a leading supplier of optical detectors to automotive manufacturers, offering a wide selection of passive and active components.
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