L-1011 Trainer Installation: Overhead Indicator Lights

L-1011 Trainer: Indicator Illumination - Overhead

Continued with the buildout of the overhead illumination today. Getting the PFCS Panel to work was a little bit of a head scratch. As part of the installation of the sim we are re-tooling all indicators from incandescent to LED lighting. LED's are, well just like the name indicates, diodes ... hence, they are directional. We initially replace all incandescent with standard midget-flanged LEDs ... however, it turns out that this is a problem. And here is why:

Since the L-1011 used 28V DC incandescent lighting it didn't matter if the "common" between the light bulbs inside a switchlight was connected to the 24VDC source or the DC Return ... the bulb would simply glow either way. But, with the LED this makes a big difference ... reverse the flow direction on the LED and it will not work at all .... because it's a diode.

Here is an example from the L-1011 WDM:

Here the common goes to the DC Return:

Here the common goes to 24V DC:

So here, Lockheed tripped me a little ... because I had not anticipated the switchlight light bulb polarity to be inverted between different panels or even within the same panel. Having learned this, we are going to have to get some LEDs with reversed polarity. That's not a problem, just something I had not anticipated. So, in the image above and below you can clearly see the difference in the LED lighting which is a clean white on the switch legend and the incandescent which has a much more yellow/red tone. 

L-1011 Trainer - Overheard Indicator Illumination (June 8th 2013)