Date: 14th July 2011
IC automatically operates auto- windshield
glass wipers sensing mist, fog, rain
Automatic windshield wiper IC from Melexis responses automatically
when mist, fog, rain or road spray begin to obstruct light
transmission through the front windshield glass in cars
and other automotives. The new MLX75308 rain sensor semiconductor
chip is a single device solution.
The MLX75308 controls all the major components found in
a rain and light sensor module typically applied behind
the front windshield of an automobile. The sensor system
consists of Near Infrared LEDs, Photodiodes, an MLX75308,
a microcontroller and, in many instances, a Network Bus
interface IC. The significant challenge addressed by the
MLX75308 is the ability to provide sensitive detection of
raindrops or mist in the presence of a highly dynamic light
load from the sun. Melexis says previous solutions to this
challenge involved expensive optical waveguides or elaborate
algorithm which reduced responsivity and increased occurrence
of false wipes. The MLX75308 separates and suppresses the
sun signal from the rain signal being measured by the photodiodes.
Automotive OEMs often prefer to optimize automatic wiper
systems to appeal to their typical consumer's preferences
and their vehicles market segment positioning. Some manufacturers
prefer a more relaxed rate of wiping, prioritizing that
over a perfectly clear windshield. Others will activate
the wipers at the slightest suggestion of rain. Running
the headlights whenever the wipers activate is desired by
some OEMs while others will consider the ambient light level
input to determine when or if to automatically switch on
the headlamps. By presenting the signal data to the ECU
on-demand and in a digital form via SPI the MLX75308 enables
the system integrator or OEM to determine how the sensor
data will affect system level behavior.
MLX75308 is designed to be flexible enough to cope with
a wide variety of windshield angles (from 40° to 90°)
as well as different tinting and shading. Sensor implementations
may demand a larger area of sensing coverage, more LED's
and photodiodes to improve rain detection thresholds or
less and fewer to optimize cost and size. Systems also need
to work over a wide current range from picoamps to milliamps
as the difference between light levels on a bright, sunny
day are vastly different than when driving at night. Melexis
says the MLX75308 can address all these options with its
programmable analog signal control chain and 16 bit ADC
and digital signal processing on chip. This combination
allows the device to address a very high dynamic range on
both input and output, claims Melexis.
The MLX75308 is configured in a 4x4 QFN package. According
to Melexis the automatic wiper control data can as well
serve for headlight control, sunlight load sensing in HVAC
controls, mist and condensation controls for automatic climate
controls. The flexibility of the MLX75308 can allow for
creative applications circuits to bring about highly versatile
sensor modules. Melexis.
Another advantage of this chip is rain light module can
easily become a sensor cluster feeding many types of information
to several different systems. Far Infrared non-contact temperature
sensors could be included to provide inside and outside
temperature measurement.
Samples of the Melexis MLX75308 are currently available.
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