My recent re-housing of an old neon nixie-flower project got me thinking about how I could re-purpose a Chinese LED lamp kit to make a self contained nixie flower that screwed into an ordinary lamp holder.
I started by designing a PCB to fit into the existing lamp housing and then crammed as many neon indicator lamps onto it as I could, in a three dimensional array shaped like a flower. Although I originally intended to have the simple drive circuitry mounted separately, there was room to mount it on the back of the PCB.
I made a transparency using a dedicated film for making inkjet transparencies for silkscreens that absorbs a deep and accurate layer of ink into a special coating on its surface.
I exposed some standard photosensitive PCB laminate with a UV nail varnish curer. I do have a proper UV exposure unit, but it was just an extra twist to use a cheap ebay item to do it. The exposure time was just one minute. The PCB laminate is a sandwich of fibreglass and the cheaper resin bonded laminate inside, with a layer of copper and then a UV-sensitive layer.
I then developed the PCB in a developer made up with 12g of sodium metasilicate in 250ml of water. When the exposed PCB is submerged and moved in the developer the areas exposed to the UV will dissolve leaving an etch resistant layer in the shape of your desired tracks. the developer solution can be stored for further use, but be aware that it can cause skin irritation so gloves should be worn and it should be stored in a sealed and marked container.
Then I etched the PCB in a Seno GS style ferric chloride etching bag. I say Seno GS "style" because I foolishly attempted to heat my original Seno bag in the microwave and melted the plastic where small amounts of the etchant were trapped in the bag clips and got too hot. So I made a new bag out of heavy duty lay-flat polythene sleeving heat-sealed in a suitable manner. Note that it took a lot of experimentation to get the sealing temperature just right to seal the bag fully without damaging it. I double sealed it, as ferric chloride leaves permanent stains on just about everything. I could have used the original clips, but I decided to get some ebay bag sealing clips just to see how well they worked.
Once etched the PCB was drilled using a hand held drill with good robust bearings, and a tungsten carbide drill bit. These drill bits are used in CNC machines but discarded when they become too worn or when they have been reground to the point they are too short for machine use. They are available at a much lower price than new bits and are ideal for home use. Note that tungsten carbide drill bits are very hard and brittle, which makes them ideal for drilling fibreglass laminate, but also makes them very prone to snapping. Use extreme care to avoid putting any sideways pressure on the drills or letting them snatch when widening pre-drilled holes with a larger drill.
I painted the PCB black, but slightly regretted doing so, since the native light colour of the PCB material may have made the lighting effect a bit brighter. The 21 neon lamps were all mounted in the desired flower shape, the circuitry added, and the PCB mounted into the lamp base. And it looks very good indeed, with virtually no running costs due to the extremely low current used.
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