Lighting In EDU

The Electronic Display Unit (EDU) display is lit by three lamps mounted on the back of the computer. When driving in the dark, the lighting is controlled by the rheostat that feeds pin 32 on the control module with a PWM signal (pulse width modulated) in the range 13 - 100% depending on the position of the rheostat. The light must be switched on. With the light switched off, there is no rheostat voltage to the EDU, which then assumes the "rheostat value" to be 100%.

When driving in daylight, the light in the cabin is measured by a light sensor on the Saab Car Computor (SCC) unit or on the front of the clock. Depending on the intensity of the light, pin 36 on the control module is fed by the light sensor that controls the lighting with a voltage in the range 0 V - 10 V.