Instrument lighting
ICM controls the instrument and button illumination with the help of:
- Brightness control buttons (rheostat function) on SIDC.
- Light sensor on rear of SID that measures the ambient light from the front.
ICM uses these values when calculating a suitable brightness for the instrument and button illumination. ICM transmits the bus message "Instrument illumination, rheostat value" with a value between 0-100% on the I-bus.
The brightness control comprises a +/- switch that provides ICM with information on the driver's choice of instrument illumination. SIDC transmits the current button press to ICM, which increases or decreases the rheostat value accordingly.
A PWM signal from SIDC on pin 4 to ICM pin 14 indicates the button (+/-) that has been pressed.
This signal is a 5V 960Hz square wave with pulse ratio 40% for the up button (+) and 60% for the down button (-). See the SID control panel table.
The light sensor that measures brightness from the front is fitted to the back of SID together with the alarm LED. The light sensors have a measuring range between 0 and 40000 Lux.