Monday, February 18, 2019

Improving the display for the DSKY substitute



With the EL wires in place, I then glued down the main light dam, which has to clear the EL wire segments  It was important to get the top surface parallel to the PCB so that it can fit flat against the bottom of the acrylic panel. I had to cut out a section of the dam the EL cabling runs, to keep it as flat to the PCB as possible.

Light dams being glued in place
Finishing off the EL display side consisted of some rice paper diffusers to be attached to the light mask and that mask in turn be glued precisely in place atop the light dam I did a final test of the firmware to ensure that the sandwich of parts was aligned properly. It was.

I turned to the indicator panel side, where I have a much simpler arrangement. There is a light dam that separates the lights into the fourteen segments, one per indicator/warning. Atop that goes the acrylic panel itself.

Mike noticed that virtually all the existing replicas and simulations have the color wrong for the two lowest lights in the left column of the indicator panel, as had I. It was presumed that all seven lights on the left column are white and all seven on the right column are yellow.

That caused people to implement the PRIO DISP and NO DAP in white, but the NASA documentation we recently retrieved shows that these were in fact yellow. The yellow conditions such as GIMBAL LOCK represent warnings that need to be heeded.

This makes sense for NO DAP, since lack of digital autopilot mode is a serious condition and should be a warning (yellow) rather than simply an indication (white). PRIO DISP warned the astronaut that the original data they were displaying had been interrupted by a higher priority piece of information.

I had already glued the light dam over the indicator panel side of the PCB, but believed I could get in with my hot air rework to make a swap and reach the pads with the soldering tool. I gave it a try.

It appears that the presence of the light dam so near to the LED is deflecting the hot air. I was able to finally pry away three of the LEDs but the fourth (there are two per indicator light) just wouldn't come loose. I finally had to pull the light dam off the board in order to make the substitution.

The new LEDs were soldered in place but glowed too dimly. The two types of LEDs, for white and yellow, required different current limiting resistors and I forgot to switch them over. White needed 1K but the yellow required 680 ohm to reach the same apparent brightness. I removed the old and put in the proper resistors to complete the repair. All is good now, so the light dam had to be epoxied back in place.

My tests with the frosted panels in place weren't good. The frosting is too heavy, reducing the light output and causing unacceptable blurring of the digits and lines. I took the acrylic out and tried to remove the layer of paint on the back, in preparation for attempting a much lighter coating.

I don't have the proper solvents on hand to remove the coating. In any case, I might just buy some more acrylic panels cut to the proper size and work with them. I am done for today.

Mask in place for EL side of the DSKY

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