SCOPE OF PROJECT
This project will make use of one Power Supply Module from a block I DSKY, one Relay Module from a block I DSKY and an early version of the EL Panel for a block II DSKY. Controlling all the elements on the display requires four relay modules, thus I can only display contents on part of the EL panel.
I chose to animate the PROG, VERB, and NOUN displays, each are two digits formed by seven segment patterns. I will also light the fixed lines and text legends. Finally, I will animate one of the signs (for the register R1). If I had a second relay module I could light up all of R1 and another sign, for example, but the modules on hand limit me.
We have some of the very precious mini-WASP connectors that were fabricated by Samtec to support our Apollo Guidance Computer restoration. I will need roughly 150 female pins for the project as defined. This is a demonstration project and as such I want those pins returned for use in future projects once this one is complete. That requires a strategy for building connectors that leave the pins 'as new' when eventually disassembled.
The normal method to build a mini-WASP (MW) connector is to take a flat aluminum plate and drill .07" diameter holes in a grid with center to center spacing of .125" both vertically and horizontally. The MW pins are pressed into the holes, compressing the nylon body of the pin. The rear of the pins are tall wire-wrap posts, which can be cut down and soldered onto PCBs to form permanent connectors.
Cutting the pin tails, soldering them, and compressing the nylon by press-fit are all irreversible acts. I had to work out a scheme that did none of those steps yet gave me a workable connector with wiring attached.
The first part of the solution is to use wire-wrap to make the connections. This winds a thin insulated wire around the post that is the pin tail. The post is a square cross section and each of the corners will cut through the insulation of the wrapped wire to make a solid electrical connection. The wire is wound several turns on the post. This does not damage the post at all.
The second part of the solution is to use a softer material for the grid of drilled holes, such that the plate itself is compressed while the nylon remains unaltered. I chose wood for this purpose. I will use a laser-cutting service to build wood plates of .13" thick hardwood with .07" diameter holes cut to hold every pin.
A second plate of hardwood, the same size as the base plate with the mounting holes, will have much smaller diameter holes at .125" spacing, just large enough to pass over the post tails of the MW pins. A dab of wood glue at the outside edges will hold the two plates together forming a sandwich to protect the MW connectors.
These won't be removable with this method, because the cumulative force needed to unset 47 or 91 pins for the two larger connectors will exceed the friction hold of the wood around the nylon bodies. If I try to pull them up, the wood will just slide up off the pins.
Therefore, these are 'permanently' installed on the modules, with the sandwich pressed down to seat the MW connector to the module side pins, then wirewrapped to provide connectivity. To remove them, I have to first remove all wire-wrap, then pull up the board and finally pull off all the MW pins that remain seated on their companion pins on the modules. This is acceptable for the purposes of this demonstration.
As with other projects requiring laser-cutting, I will use Ponoko.com as the fab to produce the wood plates I need. The designs are being produced using Inkscape (a freeware Adobe Illustrator alternative).
PLAN FOR CABLING
I will use some form of cable wrap to cover and protect the many discrete thin wires that come off each of the connectors. This is sufficiently robust for the demonstration but hardly rugged enough for a permanent installation.
There are a few outside wires that will connect to traditional connectors on the connector plates. These include external power, ground, a source of 800 Hz and all the control signals from an Arduino that will set/unset the relays to activate the module.
PLAN TO CONTROL RELAY MODULE
The relays are activated by spacecraft level switching, +28V, but the final circuit that drives all of these consist of an open collector transistor that will pull a line to ground to activate or let it float. Thus, my Arduino will need 20 such transistor circuits to fully control the project.
Some simple firmware in the Arduino will provide a command interface over serial to my laptop where I can set the codes for all the digits and the sign. A simple script can run to animate various displays on the panel.
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