Thursday, November 15, 2018

More planning for the Apollo Guidance Computer restoration


DSKY substitute planning and construction

Now that I have bought displays for the right hand panel of the DSKY substitute, I am beginning to do the mechanical design followed by PCB layout.

I will use a green 7-segment display for all 21 of the digit positions. The size is reasonable but not exact to the size, shape and tilt of the real EL panel on a DSKY.

Spec for digits on the DSKY EL panel
7-segment display for my DSKY substitute
The conundrum was image size. The real DSKY has digits that are 0.5" high but any 7-segment display that would produce such a digit is too wide and high to fit side by side in the 2.6" width of the panel, since I need five digits plus a sign display. Thus, my digits are only 0.39" high, slanted differently and have a different shape for the digit and segments.

The plus/minus sign display in front of the three registers use a green 14 segment display, the same size as the digit displays at 0.39". This will make the sign smaller than on the real DSKY. All the 7 and 14 segment displays fit across the space properly.

The EL panel also has a square in the upper left for COMP ACTY which will flash based on computer activity signals from the AGC. There are text blocks which are illuminated to describe the PROG, VERB and NOUN display areas.

Finally, there are three horizontal lines, separating the three registers, which light up. I bought a good quantity of surface mount green LEDs  to fit on the PCB to create all these lit areas. I will have to put some 'light dams' in place to keep the LEDs for one area from spilling over to the other sections of the panel.

I need a slightly frosted greenish-gray plexiglass cover over the displays and LEDs, with the text legends applied. I know how to make and apply the legends. The EL panel is rimmed with an aluminum cover, which I will need to figure out how to make for my replica.

Real DSKY whose appearance I will try to approximate
The left upper panel, with the caution and warning lights, is going to be relatively easy to make. Regular thru hole LEDs in white and yellow, respectively, will be fit on a simple board, fitted with 'light dams', and covered with a frosted plexiglass (whiter in color than the right hand panel) having the appropriate legends applied.

The buttons on the keyboard are more of a challenge to create. My aluminum housing is already cut to the size of the button openings on a real DSKY, forcing me to come up with something similar to keep the appearance reasonable.

I am still investigating materials for the 'light dams' as well as the keyboard buttons.

Erasable Memory Module repair plans

We continue to research the failures encountered and the various versions of the erasable memory modules produced. Wire failures in the modules were a continuing problem during the Apollo program, leading to a variety of fixes and versions.

The module type we own is a relatively early design. It is possible that the wire is cracked inside a fiberglass bolster plate where the wire feeds through from the outer epoxy potting material to the inner RTV-11 potted core stack. This would be more challenging to reach and repair than the later versions whose failures were out near the mounting pins.

The actual plan of action will depend on the images we can get of the inside of the module. We will be using a micron resolution tomographic scanner, similar to a medical CAT scan, that gives us a 3D image based on many slices taken throughout the module. This will give us the exact location of the break and a view to how it may be possible to access the wire for repair.

Core Rope Simulator driver design

Ken Shirriff has almost completed his reverse engineering of the two core rope simulator modules and determined what he has to build to connect to the two 39 pin circular connectors on their faces. He will based the driver on a Beaglebone board and has selected cables and connectors for his driver box.

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