8.29 Neon Open Sign

Version 1

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.

The next technical hurdle was that of diffusion. An LED is a point source of light. But illuminating artwork larger than the LED itself doesn't work, because all you'll see is a dot; diffusion is required to spread the light evenly across the artwork. Thus, clear overhead transparency film by itself wouldn't work. After trying a great many different materials, I found a thin white plastic label material that seemed just about right, and I applied it to the back of the artwork. After doing a quick test, I found that there was too much light bleeding between the red LEDs, so I painted all of their sides flat black.

The final steps were to trim the mounting plate down to the size of the art, assemble a styrene box around it, and attach the artwork to the box. Even this relatively simple process was fraught with difficulty, as two LEDs died just before I sealed up the box, and one more died after final assembly. (The failure rate of these LEDs is pretty abysmal.)

My method of making the letters light up in sequence may seem strange, even primitive. Ordinarily one might expect it to be an electronic device; instead, I made a motorized unit with a "player piano" style drum and electrical wipers to energize the LEDs in sequence. I was going to need a motor for the laundromat animation, anyway, and besides, I've always preferred a mechanical approach to stuff like this. It's also probably similar to how it was done in real life back in the day.

The final effect was extremely difficult to photograph—I'm almost embarrassed to show this video.

Version 2

Ultimately my embarrassment lead to Version 2.0. I knew what I had to do: take absolute control of the light, from the source (LED) to the target (artwork) by segregating the sign's elements as much as possible. To help with this demanding task, I modified the art a little, separating the letters a bit, and enlarging the oval. Then I began making an aperture plate by drilling four holes through 0.040" black styrene, then carefully enlarging and shaping the holes to match the size and placement of the letters (below left). Using this as a template, I then made an LED mounting plate by drilling eight #80 holes in 0.020" black sheet styrene (below right).

After threading the LEDs into the mounting plate, I pressed the aperture plate into place over them, and bonded them together with MEK (below left). Then I cut a piece of frosted acetate to use as a diffuser, and held it and the artwork over the apertures to see how evenly the letters were illuminated (below right).

Then came the most challenging and scariest step: trimming the mask assembly down to fit within the blue oval. (I'd already ruined two other assemblies, and there went eight more LEDs and a day's work into the trash.) First, I sliced the assembly down as small as I would dare with a jeweler's saw (below left), then carefully shaped the edges with nail buffers until it just fit in the oval (below right). I had extremely little margin for error, so it was a slow, iterative process.

A box to house everything came next. This I made out of 0.020" white styrene (below left) so that it would diffuse the light from four blue LEDs mounted in the corners—which was about the only thing that worked properly on the first version (below right).

After adding 0.020" x 0.060" strip styrene box sides (below left), I bonded the artwork to the face of the box with thin double-sided adhesive tape (below right). I also laminated a second copy of the artwork onto the first to make the image more light-tight, as opposed to touching it up with black paint, as I'd done before.

The only things left to do were painting the box flat black, installing the bad boy in the building, and wiring it up for the acid test.

My only regret is that the finished sign wound up 50% bigger (height and width) than Version 1, and more than twice as thick. But, that's the price I had to pay for getting better visual performance.

Version 3

Go ahead, call me obsessed... but I wanted this sign to be as good as I could possibly make it. The best thing about Version 1 was the size; the worst was poor visual performance. The best thing about Version 2 was good visual performance; the worst was its size. Was there a way to get the best of both? I was bound and determined to find out. I knew in advance the cluster of red LEDs would probably be slightly larger in order to reduce light leaks; to compensate, I changed the blue oval to a rectangle.

I started out by repeating Version 1's first step: 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.

As I had for Version 2, 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.

Even Version 2 had some light leakage, and this was due to a combination of the diffusion layer and the double-sided tape I used to attach the artwork. This time 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.

One thing I didn't like about both of the prior versions was the number of wires: 16 made for a massive, unwieldy bundle. So this time 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.

The new sign wound up the same size as Version 1—it measures roughly two and a half scale feet wide—with visual performance comparable to that of Version 2, which was my goal. As a bonus, it has simplified wiring, greatly improved cosmetics, and a vastly superior mounting solution. And now for the moment of truth:

Reference

The first two versions had an oval outline; for the third, I switched to rectangular.

Previous < Return > Next

Copyright © 2017-2020 by David K. Smith. All Rights Reserved | Site Map