Monday, January 28, 2019

Working on cosmetics of the DSKY substitute


Keyboard assembly

The replacement honeycomb arrived from the 3D service bureau and I immediately began assembling the key plungers into place. They all fit just as with the original. I think that it is a good time to make and glue in the wedges that will constrain the key movement to be more vertical. The existing clearances around the plunger allow too much wobble.

My first trial for the wedges was to use some adhesive plastic sheets, but they were way too thin to provide much improvement. Too, they were difficult to get into position and force against the plunger sides.

I then looked into some heavier clear plastic material which does stabilize the plunger in its cell. The challenge here is how to glue it to the plunger (or to the face of the cell) without glue getting onto the other side and freezing the plunger in place. I will be fiddling with the process until I can work out a way that is safe but reliable.

Display assembly

I discovered that the EL wire segments can be fitted in place of the ten discrete LEDs that form each of three lines on the EL panel side of the DSKY. If I cut wire segments from my sample wire, route the inner electrodes through my light dam and solder them in parallel, I can run them all from the single driver module.

The EL wire has an inner wire, an insulating layer, and twin small corona wires on the outside, all of which is sandwiched in a vinyl tube. By cutting away the tube I can expose the wires. I would need to cut my EL wire into three sections, each the proper length to fit on the PCB. The inner wires stick out far enough to fit under the light dam.

I only have to wire together the three inner conductors, then hook it to one side of the driver. The six corona wires get wired together and those hook to the other side of the driver cable. I expect that I will need to use hot glue to position the EL segments, the wires and my connections.

The first problem I am having is finding a way to strip the outer insulation without breaking off the two corona wires. I needed to do some research as well as practice until I end up with three proper sized segments of EL wire with the interior wires tripped and ready for soldering. It was quite challenging to get the outer plastic to peel off without damaging the corona wires or the inner phosphor/insulation.

Once that was done, I had three segments the proper length. Wires were soldered to bridge them together, the result was tested with my driver before I epoxied them down to the PCB. Prior to the glue-down, I removed all the LEDs and resistors that previously formed the lines, since they appeared to be dotted lines instead of a continuous segment.

Testing three electroluminescent lines before epoxying
I picked up the acrylic panels that I will be decorating with text, various graphics and an undercoat of gray frosting. A test fit with the cover plates proved these were ready to be painted. I also need to paint the cover plates and the aluminum enclosure in the same gray paint. I have ordered paint to get ready for making the indicator and EL panels.

The only challenge to making the indicator panel text overlay is that the text must be in the correct position on the rectangle and it must be reversed so that I can adhere it to the underside of the acrylic pane. I used Inkscape to produce the images I wanted, suitably mirrored and created PDFs to print these on a laser printer on my special transfer paper.
Mirror image text needed to create dry rub transfer
For technical reasons, the Brother brand laser printer I own does not set the toner onto the paper strongly enough to work, a known issue when using their printers with the DecalPro fx system. I will use an HP printer at the CHM when I am there on Wednesday.

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