Illumination And Dimming
The background light of the display areas and the lighting of pointers and dials is provided by orange LEDs. The light emitting diodes are designed to last the service life of the vehicle and cannot be replaced separately.
The individual display areas are only illuminated when there is a message displayed in the relevant display area. However, for reasons of visual appearance, two adjacent display areas are always illuminated at the same time.
The pointers and dials are only illuminated when the lights are switched on and they serve as a function indicator for "driving light ON". The brightness of the LCD display as well as all indicator and warning lamps is adapted to the lighting conditions in each case using a phototransistor.
The brightness signal is calculated in the instrument cluster from the values of the photo-transistor (1) and the dimmer wheel. This brightness signal is also made available via the K-CAN System to other control units in the vehicle. The instrument cluster is thus used as the "dimming master".
The contrast setting of the LC display is automatic, depending on age and temperature. For the temperature compensation, an NTC resistor is fitted to the LC display. The contrast voltage is then determined according to the temperature by the electronics in the instrument cluster.
In order to take account of ageing over time, a counter is installed in the instrument cluster to record the operation time by the hour. With increasing age of the LC display, the contrast voltage is adapted to maintain a consistent contrast.