cast their beam in the direction of the curve a driver is steering
through and ensure better visibility on winding roads. Within
the headlights are small electric motors that turn them. A sensor
like the TCPT1350X01, which can operate at temperatures as high
at 125°C, is used to encode the motor movement, thus controlling
the motion of adaptive headlights.
Rain/light/tunnel sensors are found on high-end vehicles.
Their primary function is to determine the amount of rain falling
on the windshield to control the speed of the wipers. They can
also be used to automatically turn the headlights on and off as
the vehicle enters and exits a tunnel. Finally, they can determine
the amount and direction of light as an input for climate control.
My son asked me to turn off the air conditioning last weekend as
we drove north to San Francisco. I was sitting in the sun and had
to explain to him that our car did not have a “sun” sensor, so the
“dad” sensor was the primary input. Each of these features relies
on infrared emitters and photo detectors to function.
Ambient light sensors have been used for decades to turn on and
off headlights. With the introduction of high-resolution digital
ambient light sensors, rear-view mirrors on high-end vehicles
began to feature an auto-dimming function to reduce the glare
from the headlights of vehicles traveling behind them at night.
In addition, as larger and larger LCD monitors find their way into
the dashboard of cars, the ambient light sensor will automatically control their backlight intensity. The screen will be bright
during the day and dimmed at night for optimal viewing. This
same sensor can be used to control the accent lighting in the
Many of these LCD monitors are used to control cabin features
such as climate and sound systems, where a touch screen allows
users to navigate through the menu of options. However, focusing on the touch can be as distracting as texting while driving.
Instead, manufacturers are evaluating the use of gesture control,
where a swiping motion is sufficient to move from screen to
screen and up and down a menu system. Common gesture sys-
tems being evaluated include multiplexed infrared emitters with
a reflective proximity sensor located above the monitor. They are
precise enough to allow a touch-like selection without having to
actually touch the screen as shown in the following gesture evalu-
Gesture control evaluation board
Wireless headphones are used with DVD players to entertain the
back row occupants. Seldom — I couldn’t say gone — are the
days where “how much longer” is the mantra. Due to interference concerns, wireless car headphones use infrared emitters to
transmit the sound and IR receivers to receive and provide the
initial decoding of the sound. An IR receiver is also found in the
DVD to control on/off, play, and other remote control functions.
Moving out of the cabin to the outside of the vehicle, Ford
introduced a foot-activated lift gateway in 2012. An RF sensor in
the car detects when someone with the key fob is in proximity.
It then enables a laser sensor under the rear bumper to detect
reflected light off of the foot, which results in the trunk or gate
opening. This could also be accomplished with a SurfLight™
infrared emitter with a collimating lens. Rear-view or back-up
cameras could soon be a mandated feature on passenger vehicles.
These same emitters can be used for nighttime illumination.
Night vision systems use either active infrared or passive
infrared systems to increase the distance a driver can see beyond
the reach of the headlights or in poor driving conditions. Active
infrared systems pulse infrared emitters that are synchronized to
a CMOS camera. The infrared will reflect off of objects beyond
the vehicles headlights, and a heads-up display shows the reflected images. These systems are particularly useful in rain and snow
and can extend vision to over 200 meters. Passive infrared sensors
do not emit infrared light. Instead they are sensitive to the far
infrared wavelengths and use a thermographic camera to display
Lane departure warning systems warn the driver if the vehicle
is moving out of its lane on a freeway, unless a turn signal is
on. They do not work below a certain speed, typically 35 mph.
Camera-, laser-, or infrared-based systems are used to detect the
lane markings. Camera-based systems parse the image, looking for
straight or dashed lines to the right and left of the vehicle. Laser
or infrared systems depend on the reflective contrast between the
line and pavement and will be positioned at the corners of the
vehicle. Both methods rely on visible lane markings. They typically cannot decipher faded, missing, or incorrect lane markings.
Markings covered in snow render the system inoperative.
LEDs have made steady headway. They have replaced the bulb
in most applications involving backlighting: instrument clusters,
infotainment systems, switch backlighting, and climate control.
They are used for brake lights, hazard lights, puddle lights,
distinctive decorative lighting, and warning lights for blind spot
and rear crossing alert systems. As color rendering improves,
they are starting to be used in door lights and for cabin lighting.
Higher end vehicles are allowing drivers to customize their interior color by using RGB LEDs that can be dialed in.
Within twenty years, hands-free driving will be a reality, at
least on the freeway. Optoelectronic sensors will be doing the
bulk of the sensing for us. ECN
Rain sensor (Vishay)