Author Topic: Neon Open Sign  (Read 49 times)

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    • David's Modeling Journey
Neon Open Sign
« on: September 20, 2020, 07:30:55 AM »
This late addition is courtesy of some brainstorming on the Railwire. I'd resisted having blinking stuff, but this would be so tiny that it shouldn't be annoying. It blinks in the classic old O-OP-OPE-OPEN-off-OPEN-off cycle. It turned out to be considerably harder to pull off than I'd expected. I thought I'd just print some artwork on overhead transparency film, glue some LEDs to the back of it, and Bob's your uncle. But nothing could have been further from reality. I was thinking in terms of fitting the LEDs to the sign art; the only practical way to accomplish it, however, was the reverse: pre-assembling the LEDs, then fitting artwork to them. I learned this after printing dozens of signs and wasting nearly a dozen LEDs.

The problem is that CA doesn't like bonding with the epoxy resin used to encapsulate the LEDs, and their tiny size only makes matters worse. Thus it was virtually impossible to bond them to the back of the artwork. What I had to do instead was make a mounting plate by drilling 16 #80 holes in 0.020" sheet styrene, threading the LED wires through the holes, and rigidly securing them to the plate with a generous amount of CA on the back. The wire leads for the four red LEDs had to be bent over 90 degrees right at the chip so that they would sit flat on their backs; this was probably the most nerve-wracking step, as about a third of the time the solder connections would fail. The four blue LEDs were mounted on their sides at the corners of the artwork so that the light raked across the back of the oval.


I started out by making a mounting plate for the four red LEDs by drilling a grid of holes (above left and right), bending the LED leads, and bonding the LEDs to the plate (below left). This time I used black styrene instead of white to help further isolate the red LEDs from the blue. Next, I made a black styrene box around the LEDs, and then proceeded to flood the assembly with black acrylic paint. I kept applying more paint until the spaces around the LEDs were completely filled (below right).


When the black paint was fully set, I sliced off the excess, then gently sanded down the surface with fine-grit nail buffers until the faces of the LEDs were exposed. Next, I trimmed away the sides to make a self-contained unit for just the letters (below left), carefully sanding down the sides until I was most of the way through the edges of the styrene box so it would be as small as possible.


I attached the red LED unit to a piece of white sheet styrene for the blue LEDs, except this time I painted the edges of the red LED unit with white acrylic paint to improve blue light diffusion (above right). I made a box around the perimeter of the sign with white strip styrene, then I installed the blue LEDs—opposite from before: this way it helped position the blue LEDs much more precisely to keep things as compact as possible. Finally, I trimmed everything down to its final size (below left). Incidentally, I kept the LEDs lit during the entire construction process: it helped prevent "surprises" if I happened to make a mistake and not realize it.


I experimented with a variety of different diffusion materials and artwork, and also used CA to assemble it rather than tape. I found the best combination was to sandwich the frosted acetate between two layers of artwork (above right). Again, there's still a little light leak, but there always will be as long as diffusion is required.


I connected all of the cathodes together, and also tied all of the blue LED anodes together (above left), reducing the wire count down to six—much more manageable. To further streamline the wiring, I used brass wire stock to make rods that suspend the sign in the window (above right), which I used for the cathodes and the blue anodes, leaving me with only four wires (below) that I'll just tuck behind the door frame.

And now for the moment of truth: