Functional description

The following functions of the Head-Up Display are described:

Operation of the Head-Up Display 

The Head-Up Display is controlled using the following operating elements:

• Button for switching Head-Up Display on and off
  NOTE: Depending on the model series (e.g. F25), the head-up display can be switched on and off exclusively via the central information display.

  With the button in the driver assistance system operating facility, the Head-Up Display is switched on and off from terminal 15 ON. The operating facility for assist systems is connected via LIN bus to the footwell module (FRM). A bus signal from the footwell module to the instrument panel (KOMBI) indicates the button has been pressed.

  The instrument panel activates or deactivates the transmission of image data to the Head-Up Display via the LVDS data line. The instrument cluster transmits a bus signal to request that the backlighting in the Head-Up Display is switched on or off.

  A bus signal from the footwell module to the HUD control unit indicates the button has been pressed.

  The button has 2 functions that are activated by pressing the button for different lengths of time.

  • Short press of the button, under 10 seconds

    Switches the Head-Up Display on or off

  • Long press of the button, more than 10 seconds

    The test function is started. This mode is intended for service (e.g. system test). As soon as the first test function is displayed, other test functions can be called up by briefly pressing the button.

    Pressing the button again for longer than 10 seconds terminates the test function.

• Dimmer for instrument lighting

  The knurled wheel for the instrument lighting is part of the light switch. The LIN bus connects the light switch with the footwell module (FRM).

  The footwell module provides information regarding the dimmer setting for brightness control of the instrument panel (KOMBI), the central information display (CID) as well as the Head-Up Display (HUD).

• Controller for selecting brightness of head-up display in central information display (CID). Also for adjusting the position of the virtual image and for selecting the displayed information.

Characteristics when switching on 

The HUD control unit receives the status terminal 30B ON via the K-CAN. To protect the projection display against direct solar radiation when parked, one mirror is swivelled away while the vehicle is going to sleep. As of terminal 30B ON, the mirror is swivelled from the parked position into the beam path.

The Head-Up Display is partially operational when terminal R is switched ON. That means:

• The projection display is initialized but information is not yet displayed.
• The Head-Up Display is able to communicate with other bus users via the K-CAN data bus.
• The LEDs are off.

The Head-Up Display is operational when terminal 15 is switched ON. That means:

• If the status "Head-Up Display active" is selected in Personal Profile, the Head-Up Display is switched on automatically.
• The projection light source is switched on or off when the button for switching the Head-Up Display on and off is operated.
• The automatic adaptation of the display brightness is activated.
• The image orientation of the virtual image can be height-adjusted.
• The information to be displayed can be selected.

Projection of virtual image in front of the vehicle 

The Head-Up Display projects a virtual image. In other words, this means that an image is created that appears to be projected onto the air, without the use of a display surface for the image (e.g. a projection wall or similar). The image is generated on a projection display in the Head-Up Display and deflected by the windscreen in such a way that the driver seemingly sees the image floating above the engine compartment lid. (The effect of the virtual image is the same as when looking in a mirror: you do not see yourself on the mirror, rather behind it.) The size of the virtual image is approx. 20 x 10 cm (width x height). The virtual image can only be seen from a defined area from the driver's side.

Automatic adaptation of display brightness 

The automatic adaptation of display brightness prevents major sudden changes in the brightness of the Head-Up Display when the vehicle moves between different ambient lighting conditions (e.g. from light to dark and from dark to light when driving through a tunnel).

The automatic adaptation of the display brightness depends on the ambient brightness, the brightness adjustment and the dimmer setting of the instrument lighting (only with light ON) or the brightness setting via iDrive.

The ambient brightness (day, night, dawn/dusk, sunshine, etc.) is picked up by the rain/light sensor (part of the rain, light and precipitation solar sensor). This also picks up the brightness in the area of the virtual image to ensure optimal brightness control. The value of the brightness adjustment (difference between basic setting and individually set display brightness) is stored in the Head-Up Display. When the lighting is switched on (terminal 58g, lights ON) the brightness of the Head-Up Display is also influenced by the dimmer setting of the instrument lighting of the brightness setting via iDrive.

The brightness adjustment takes into account the individual brightness setting for the Head-Up Display, deviating from the basic setting. The individual brightness setting is made on the CID (Central Information Display) using the controller. The set value is stored in the Personal Profile in the HUD control unit.

Prioritisation of displays, switch-on characteristics 

The information in the Head-Up Display is classified according to priority (= importance for the driver). Displays with low priority are overwritten by displays with higher priority.

• Priority 1:

  Warnings of cruise control

• Priority 2:

  Check Control messages

• Priority 3:

  Test function (= auxiliary materials when troubleshooting without diagnosis system)

• Priority 4:

  Navigation instructions

Image generation 

The picture signals for the screen mask are transferred from the instrument panel (KOMBI) via the LVDS data line to the HUD control unit. The switch-on and switch-off signal as well as the information for the screen mask are output by the corresponding control units (e.g. headunit) as bus signals. The HUD control unit evaluates the bus signals received via the K-CAN and forwards the processed image information to the components of the Head-Up Display.

The background color of the Head-Up Display is black. The contents of the Head-Up Display are displayed as follows:

• Orange as standard color
• Red or yellow for warning messages
• Green for set speed
• as well as levels of grey of the above colors

The 4 colors orange, red, yellow and green are generated as follows:

• Special layout of the LEDs
• Corresponding activation of the LEDs by the HUD control unit.

The size of the indication range of the virtual image is approx. 20 x 10 cm (width x height). To make the contents of the display easier to read, the display area is divided into an upper section and a lower section. Navigation instructions and Check Control messages are displayed in the upper section. Speed-related information is displayed in the lower section. Which display contents are shown is set in the central information display (CID) using the controller.

Setting the display area of the Head-Up Display 

The virtual image can only be viewed completely and properly if the position of the eyes is within a certain area on the driver's side. Outside this area, it is not possible to view the virtual image completely. The height of the position of the virtual image can be shifted (± 5 cm). In this way, the user can alter the determined eye position area by horizontal height adjustment and adapt it to his/her requirements (via CID and controller).

Position of the virtual image 

It is possible on the CID (central information display) to use the controller to adjust the position of the virtual image to the seat position of the driver. The set value is stored in the Personal Profile in the HUD control unit.

Switching off the Head-Up Display 

The Head-Up Display is switched off either using the button for switching the Head-Up Display on or off, or at terminal 15. The head-up display can always be switched on and off via the central information display.

Index	Explanation
1	Head-Up Display (HUD)
2	Plug connection 8-pin, connection to K-CAN and voltage supply
3	Plug connection, four-pin, connection to LVDS data line