Saturday, February 23, 2019

Building cables, steady progress on the display, fixing the core rope simulator module



One repair to the PCB remained - installing a jumper from a nearby via that has connectivity down to the Arduino, carrying the signal over to the four current limiting resistors for the COMP ACTY LEDs.

At first it appeared the only way to make this work is to drill through a side wall of at least one of the light dams - 3D printed plastic shapes that are epoxied onto the face of the PCB. However, there is a very teeny crack under the dam near the LEDs in question, and another under the indicator side light dam.

If I could find a small enough wire that can still carry 20ma, able to be forced under the two light dams, then I could make the repair without drilling. And, in fact, I found such a wire, routed it under the dams and made the connections to the resistors on one side and the live via which is still connected down to Arduino pin 30 where I control the COMP ACTY indication.

Jumper in place to repair connectivity of COMP ACTY drive signal to LEDs
I received some smoked tinted gray plexiglass that I ordered as a replacement for the spray paint frosting, which I was unable to get applied in an even but thin coat to allow enough light through. In the interim I experimented with another option, some grey tinted plastic (antistatic bags that come with electronic components).

I was happy enough with the brightness, grey color imparted to the panel and the only area I still needed to work on was the diffusion or frosting for the legends (COMP ACTY, PROG, VERB and NOUN). I did a test with some diffusion paper under the gray bag under a clear acrylic panel and was reasonably happy with this.

Testing of diffusion and coloring for DSKY - no diffuser on upper right legends - panels loose on top
It is possible that I could make a mask and spray paint some frosting on the rear of the acrylic panel, just in the areas where the text shows through. This will depend on how I feel about the display as it sits now. I am on the fence with this, I could either wrap commit to the diffuser paper, gray antistatic bag material and acrylic, or work further on diffusing so the individual LEDs are no longer visible.

My tinted plexi came in and was just perfect for the role, even better than the antistatic bag material. I took this over to Tap plastic to be cut into panels of the proper size. After checking out the stack once again, I decided that this side is ready for assembly.

Another area where I am dissatisfied is the light dam for the indicator panel. The openings do not properly line up with the lights, text legends I created and the top cardboard mask. I took the dimensions I used to cut the light mask and updated the 3D printing design.

With that done, I have uploaded the design to the 3D service. In the meantime, I had to safely remove the existing light dam which was epoxied in place.  That wasn't as difficult as I had expected, so now the PCB is ready for when the new part arrives.

Because I used real electroluminescent wires to form the three continuous lines that separate the R1, R2 and R3 rows of digits, it needs a high voltage supply to operate. I have such a driver module, which is small enough to fit in my enclosure, but it is fed with 9V from a battery which is operationally unacceptable.

I also need these lines to switch off when the AGC is in standby mode, I decided to power these from the BPLUSSW (+14V switched line) coming from the computer. When the computer is in standby, no power for the EL driver, otherwise they light up. I only need to drop the voltage down from 14 to 9 for the driver module.

An adjustable buck converter is just what I need. I found a nice small board with a regulated, adjustable converter, only a few tens of mw power loss for the conversion; these should arrive on Tuesday and I will have the board wired into the display PCB soon thereafter for testing.

Buck converter board to drop +14V from AGC down to 9V for EL driver

I began to put together the cables for the DSKY substitute. One short one will run between the display and keyboard PCBs. Three cables run out with AGC inputs, AGC outputs and miscellaneous AGC signals, all to be connected to power supplies or the Apollo Guidance Computer itself. Finally, a small power cable runs out to supply the two boards with 5V for their operation.

I had bought cable supplies so that I could begin to fabricate the end that fits onto the DSKY printed circuit boards. I have a dual row 2x12 connector, a single 8 pin connector and two single row 10 pin connectors on the display board, plus a barrel shaped power connector.

The display to keyboard cable has a single row of 10 pins on each end, but due to a previously confessed error in the design of the display PCB, one of those lines is intended to deliver 5V to the keyboard but instead feeds 28V on the display side.

I had to modify the cable so that pin 9 is connected on the keyboard but routed away from the connector on the display board and hooked to a source of +5V. A large via was located into which I soldered a header socket for a single pin to provide 5V. I also glued  the hole on the display connector so that 28V cannot get on to the wires if the plug is reversed by accident.

Keyboard to Display cable for DSKY
The next cable to build was a 2x12 ribbon cable, which I could leverage from PC components. It carries 28V from the spacecraft supply (through the AGC) and 23 signals that come to the DSKY from the AGC. This fit nicely; thus I could proceed to build the others.

AGC inputs cable (2x12)
I moved on to the 10 conductor cable, which carries the 8 output signals from the DSKY to the AGC, as well as providing a common ground. This was also pretty easy to build up, using superglue to accrete the jumper pin housings together until I had a block of 10. With both the keyboard cable and this one, I use a black wire at the ground end to help maintain proper orientation. I cut the tip off the unused pin 9 and put glue in the PCB connector.

AGC outputs and ground cable
The last of the signal cables is a 8 conductor ribbon cable which brings two loosely defined AGC signals to the DSKY - LGC Warn and AGC Warn - then loops two pairs of lines which run through the DSKY in the spacecraft but have no role in what is displayed. I used glue to accrete jumper pin housings to form these six lines, plus there is one inactive spare.

The last pin is the +14V signal, BPLUSSW, which the AGC switches off when in standby and on when it is running. That signal triggers blanking logic on the DSKY to darken the panel. When I have no BPLUSSW voltage, it shuts off the three horizontal lines, blanks the legends PROG, VERB and NOUN, turns off the digital displays and signs, and blocks the COMP ACTY from lighting. This causes the EL side of the display to go dark.

Having the cables built is only part of the challenge. I still have to determine how I will route these out of the DSKY enclosure - what kind of hole and on what face of the box. Next, I need some kind of junction board or box that we can use to connect from these cable wires to the wires coming from the AGC.


As Ken continues to test his driver for the Core Rope Simulator modules, which plug into the AGC and feed results in lieu of plugging in the six actual core rope modules. This provides the 36K of read only memory that contains the programming for Apollo missions.

Ken's driver board will store all the captured images we have of various CM and LM mission software, allowing us to select one to be accessed by the AGC.

Raytheon built this using a technology that was popular for a short while, mainly the early 1970s, called a DipStik. This is a plastic enclosure that mounts six dual-inline (DIP) integrated circuit chips on the inside and has solder tabs on the top and bottom for connection to the rest of the circuit.

These are not the most reliable of sockets for the chips. it presses the chip legs between contacts on the base and top of the DipStik, with screws at both ends to tighten the top onto the base. The plastic bows up in the middle, however, making contacts on the middle two chips erratic or open.

It had a bit of springy metal that was intended to press the chips down on the top contacts, but that doesn't solve the continuity issues on the base contacts. Worse, the springy metal disintegrated on all our DipStiks, a sample of about a dozen units. After we picked the fragments out, the bowing was the next major issue, one we still must resolve.

While Ken was opening and closing one DipStik unit, the screw snapped off in the base. This was highly surprising since he was using mild finger pressure, not even a screwdriver applied to turn it. Marc removed the fragment from the base and then disassembled the top to unfasten the broken screw top.

It was an unusual shape, with a groove milled for a circlip style set of restraining tangs, then a conical shape down to the threaded end. Marc did careful measurements, found a similar style screw with a larger diameter, and then milled it all down on his lathe and put on threads with a die. It was a good match except it is a more silver color and has a Phillips head top rather than a slotted top, but worked just great.


  1. Hi Carl
    This may be a little late but looking at your progress with the lights, something came out from the back of my mind. Before light meters, people used to be able to compare lights sources quite accurately this way.
    You take a piece of aluminum foil and place a thin slab of paraffin wax on either side. I think today one can use two pieces of cloudy plexiglas. It seems the eye can see the difference of two lights right next to each other but it is not so good if spread in space or time.

  2. Thanks Dwight.

    I brought my video of the test and compared it to the 1401 control panel, which is using a similar approach to the 1130. I think I need to dim the LED a bit and shift it a tad away from the bright yellow, but I think I am in good shape.