| The following components are always involved in the illumination of buttons and displays: |
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| Onboard supply control unit -J519- |
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| Phototransistor in control unit in dash panel insert -J285- |
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| Switch and instrument illumination regulator -E20- in light switch -E1- |
| To help the vehicle occupants locate the buttons and controls, and to ensure display information is readable, button symbols and displays are provided with illumination featuring a dimming function. A distinction is made between button illumination dependent on exterior lighting (terminal 58s), button illumination dependent on exterior lighting and the ignition (terminal 58st) and display illumination (terminal 58d). |
| The onboard supply control unit -J519- controls the button and display illumination, and as such is designated the dimming master. The dimming master calculates the dimming values for terminals 58s, 58st and 58d depending on the ambient brightness and the illumination intensity required by the driver. |
| The ambient brightness is determined on the control unit in dash panel insert -J285-. For this, a phototransistor is fitted in the instrument cluster to register the brightness. The control unit in dash panel insert -J285- filters and attenuates the raw value and then transmits it over the CAN bus to the onboard supply control unit -J519-. |
| The illumination intensity desired by the driver is adjusted on the switch and instrument illumination regulator -E20-, which is integrated in the light switch -E1-. The adjustment setting is transmitted via LIN bus to the onboard supply control unit -J519-. |
| Because of the differing requirements, the three dimming levels are independent of each other, and assume different values. |
| The onboard supply control unit -J519- outputs the terminal 58s and terminal 58st dimming values as both discrete PWM signals and bus signals. The terminal 58d dimming value is only output as a bus signal. |
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