Adjusting Search Illumination/Lighting

The brightness of the pushbutton unit illumination can be adjusted using the instrument and search illumination rheostat (A1r1) of the instrument cluster (A1). The brightness is adjusted using the duty cycle of terminal 58D (see below).







Signal flow:
- If the side lights are switched on, the front SAM control module with fuse and relay module (N10/1) passes the message "ON" on the passenger compartment CAN.
- The instrument cluster (A1) receives this message and passes the message "duty cycle term. 58D" on both the passenger compartment CAN and on the engine compartment CAN.
- Various control modules receive this message and control the amps (L) of the pushbutton unit illumination with the square-wave voltage U(58D)







Duty cycle term. 58D
The lamps of the pushbutton unit and switch illumination are controlled by a square-wave voltage U(58D) (see above figure):
- The lamps are supplied with power during the time (t1) which is then followed by a pause After the pause the lamps are supplied with power again and so on.
This alternation of power flow and pause happens so quickly that the human eye cannot detect the lamps flickering.
- The ratio of times t1 to T is called the duty cycle, whereby T is the constant cycle duration and t1 is the time during which power flows during a cycle.
- The greater the duty cycle (that is to say the power flow duration t1), the greater the average power and therefore the brighter the lamps.

The figure shows the voltage shape U(58D) as applied to the outputs term. 58D of the various control modules. The upper and lower diagrams illustrate a duty cycle of 80% and 40%, respectively.

A duty cycle of 100% corresponds to normal direct voltage. Power is not supplied when the duty cycle is 0%.

Advantages of this brightness control:
- Considerably more efficient,
- Brightness of lamps depends on number of lamps (load),
- Each control module that is connected to the passenger compartment CAN or engine compartment CAN can control the lamps with the brightness specified by the instrument cluster (A1).


NOTE:
When the side lights are OFF, the instrument cluster (A1) sends the message "duty cycle term. 58D = 0%".
When the side lights are ON the sent duty cycle can be adjusted from 12 - 100% using the instrument and search illumination rheostat (A1r1).