Display Brightness issue

7.5.6      Main Lighting Configuration (Page 5 of 12)

The source of the lighting for the IFD5XX/4XX can be the bezel photocell sensor or the dimming bus.  28VDC, 14VDC, 5VDC and 5VAC dimming buses are all supported and are automatically detected by the IFD5XX/4XX.

The AviCurve tracks the aircraft dimming bus as follows:

Figure 15: Lighting Curve - AviCurve

1. Select desired dimBus Type;
2. Select the dimBus Max Voltage field;
3. Push the right bezel knob;
4. Set the dimming bus to the maximum value (e.g. full clockwise position on dimming rheostat);
5. Push the right bezel knob to store;

One of the questions/scenarios folks are asking is why a 100% slope value doesn’t result in 100% brightness value.  This was intentionally done through a lot of empirical testing in a darkroom and during night flight tests.  However, field experience has shown a wider breadth of aircraft lighting configurations than had been anticipated and we are looking into making a change in the software in an upcoming  release to enhance the behavior of the AviCurve.  In that potential change, setting a dimBus slope of 100 will result in maximum brightness instead of the 21%ish that can currently be achieved.  This should achieve the desired curve at the beginning of this thread (copied below for completeness).

x1 = dimBus Min Voltage

x2 = dimBus Max Voltage

y1 = dimBus Minimum

y2 = dimBus Maximum

Slope = (y2-y1)/(x2-x1)  (basic math here, rise over run, etc.)

So, why is there even a need for the slope parameter (dimBus Slope), and what is it supposed to do?  (I asked this same question in my May 16 post)

I see why there needs to be a photoSlope.  Because when on the photocell, the min and max ambient light (x1 and x2) are not configurable.  Hence the need for the photoSlope.  But for the dimBus, the min and max voltage is configurable, so there is no need for a separate slope parameter.  I wonder if the Avidyne engineers got bogged down with this dimBus slope parameter somehow?