Tuesday, March 26, 2019

Nearing the finish line on the physical assembly of the DSKY substitute



The acrylic panel for the EL side is only 1/8" thick but my cover anticipates a 1/4" stack. The indicator side is built on a 1/4" panel so that is good as it sits. I had a 1/8" clear acrylic piece cut at Tap Plastics and with that could complete the glue-up of the two panels in their covers.

The panels I produced fit into a cover plate, with a bottom plate that will hold the acrylic panels in place inside the cover assembly. I used a dab of acrylic glue to anchor the panels into the covers, then more acrylic glue to hold the bottom plate to the rest.

Panels glued into cover assemblies with base plates
These will need 24 hours to set up strongly enough for insertion and gluing onto the aluminum faceplate. I intend to use Epoxy for that step since they have to bond to metal. I coated the panels with a clearcoat of paint to protect the surface of the lettering for both and the light mask on the indicator panel. The result wasn't as nice as I expected - a kind of pebbly finish to the clearcoat. In addition, streaks of the acrylic glue fell on the surface creating unintended lines on the surface.

Also, the acrylic glue wasn't bonding to the cover - whatever plastic used in the 3D printing service doesn't melt with the same solvent as acrylic. I will have to epoxy the panels into the covers, before epoxying the entire covered panel into the faceplate.


The glue on my coil springs had firmly set, allowing me to put together the PCB and honeycomb assembly. The bolts holding together this sandwich are part of longer standoffs that will position the top of the keyplungers at the right height.

I needed to do some minor modifications to the bottom of the honeycomb to better fit the PCB underneath it. One of the rows of pins for the Arduino Nano jut up  and impinge on the bottom rail of the honeycomb. In addition, a rework to the PCB placed two wires that run left to right under other rails of the honeycomb. I had to dig out space for all of these to allow the remaining rails to sit flat on the PCB.

The goal is to have the top of the plunger level with the underside of the DSKY faceplate. The keycap itself will add a bit of height and bring the key face that is touched by the user to the proper recess into the faceplate. I measured, fine tuned the supports, and assembled it all.

I checked the behavior of all the keys and was quite pleased. They move realistically, with the same downward travel and resistance as the real DSKY. All that remains to do here is to add the keycaps and this part of the project is complete.

I temporarily put on the faceplate so that I could glue on all the keycaps themselves. To do this, I need the plungers in their final location and the edges of the openings in the faceplate will let me register the keycap with uniform gaps on all four sides.

Keycaps glued in place on plungers

The display section was ready for its final mounting in the enclosure. After checking the height of the mounting posts one last time, I attached all the cables, routed through the hole in the back.

I did another test of the circuit that detects the presence of the switched 14V (BPLUSSW) from the AGC as it is used to blank or light the EL side of the DSKY. It is properly delivering 5V to the Arduino pin when the 14V is present and dropping to 0 when it is off.

Next I had to test the relay that switches on to illuminate the legend text on the EL panel - VERB, NOUN and PROG - as those must switch off when 14V is not present. This too worked perfectly.

Finally, I had to verify that the boost board and driver for the electroluminescent wires are switched on and off when 14V is changed. I used a small relay to drive the power to the boost board. The boost converter board, relay and EL wire driver module had to be mounted to an insulated carrier, something I implemented with plexiglas.

The relay and boost boards screw down directly onto the plexiglas while the EL driver module needed epoxy to hold in place. I then had to develop a way to hold the plexiglas board down on the bottom of the enclosure, under the DSKY display PCB. I used some plastic screws thru holes in the bottom of the enclosure.

EL power assembly
Before I finalize the cables and the EL power assembly, I dropped the display board down and maneuvered its screw ends through the holes in the bottom of the DSKY enclosure. After it was arranged in the proper position, I laid the cover over it to ensure that all was aligned properly. All looks good.

Test fit with display PCB inside and panels/covers in place
With the keyboard assembly ready and in place inside the enclosure, all the visible parts of the DSKY are now in their final configuration. Next up is securing the El power assembly to the inside of the enclosure, wiring it to the display PCB, epoxying the panel/covers down, and installing the faceplate.

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