Adding a Personal Touch to Automotive Interior Lighting via lin by Michael Bender, Melexis

For ambient lighting to have real impact on the in-vehicle environment and add to passenger/driver comfort, a large number of solid state light sources need to be deployed throughout the cabin interior - being located in the foot wells, along the dashboard, across the underside of the roof, the door panels, etc, as well as illuminating certain mechanical parts (such as the interior door handles, cup holders and such like). Progress already made in the field of optoelectronics enables the combining of red green blue (RGB) light from single package emitter devices dispersed throughout the vehicle cabin - making it is possible for a broad spectrum of colors to be produced without the need for separate LEDS for each primary color.Nevertheless, the cost associated with providing interconnections to all of these RGB LEDS has the potential to seriously restrict ambient lighting implementation, with the effect being that it might only be considered for luxury cars. This would be unfortunate as there are clear opportunities to jazz up the interiors of mid-range and entry level car models too if the price is right.

With the curbing of any financial outlay required for implementation deemed to be of paramount importance, utilization of the local interface network (LIN) has emerged as a way to control the arrays of LEDs in ambient lighting systems - thereby making use of an existing bus infrastructure. The lightweight, single wire LIN bus supplements the communication carried out by the high performancebut costly controller area network (CAN).As each RGB LED module can beconnected to the LIN network there is no need for any addition to the car’s cabling. As a result the overall system costs are kept to minimal levels, plus the vehicle’s overall weight is not increased - thus avoiding the fuel consumption penalty that would be observed if current point-to-point wired arrays were used.

As there is the need for a large number of solid state light sources to be deployed throughout the cabin interior, it is vital that all the modules are the same (in terms of hardware and software) for logistic reasons. To simplify the car production process together with the need to individual control a single module it is necessary to implement a system to detect the position of a single module in the car. This is done with the help of the already field proven auto-configuration mechanism, based on bus-shunt (already used in climate systems). This implemented system allows the position of the modules to be detected during the EOL process of the car. As a result, though all modules within the car are physically the same, they can be addressed via LIN on an individual basis. Melexis offers a simple-to-use reference design with the LED emitter andthe driver electronics all contained on a highly compact board.