Soon after ordering the PCB, I came across Seeed Studio’s acrylic laser cutting service. Once the PCB is assembled and tested, it would be nice to have an acrylic case for it.
The current trend for acrylic cases is the plastic sanga. The other option is the case put together with slots and screws. I don’t much like this look so I opted for the plastic sanga.
The normal approach is to have two sheets of acrylic, one above the PCB and one below it. The acrylic sheets are roughly the same shape as the PCB. The PCB I have is roughly 50x50mm. The acrylic sheet size offered by Seeed is 100x100mm. This means that I can have two copies of both the top and bottom sheets within that space. Ideally, I would have liked to have the acrylic sheet a bit bigger but there is not enough space for that. Unfortunately, the maximum size for acrylic cutting is also the same (or exact multiple) as the maximum size for PCBs.
I opted for no overhang on the acrylic sheet. The sheet is exactly the same shape as the PCB. Fortunately, the PCB is slightly below the maximum size. This allowed me to have a bit of a gap between copies of the pieces. With laser cutting, the two pieces may best not have a common dividing line but have a bit of a gap. The pieces should also have a bit of a gap from the edge.
The assembled PCB is not exactly low profile. It is not SMD but exclusively through-hole. The electrolytic caps are of the radial type and are quite tall. The main electrolytic cap of 1000uF/35V is especially tall. The top sheet is designed to be 15mm over the PCB. This clears all components except the largest cap. To accommodate this, a hole is cut in the top sheet allowing the cap to stick out and make a feature out of a problem. There are four mounting holes in the corners. The bottom sheet is plain and just has the mounting holes.
After the whole unit is assembled, it should still be possible to connect and disconnect wires to the unit. In order to facilitate that, oval slots have been drilled above the PCB terminals, allowing access to the screws. There is no access to the ICSP connector once the top sheet is installed. This should be OK as the PIC should be programmed before the unit is installed and further access is unlikely. If it is needed, the top sheet will have to be taken off.
The next step was to go about getting the hardware to put it all together. I ordered assorted screws and other paraphernalia to help put it all together. As they will be in plain view, I opted for stainless steel and brass versions wherever possible. I did look at the plastic alternatives as well but preferred the metal options. I opted for allen bolts. Galvanised or blackened versions are available as well but I opted for stainless steel.
From L to R: M3x30mm socket head stainless steel screw, M3 stainless steel nut, 12mm and 4mm brass hex M3 spacers, M3x30mm clear plastic screw
The order of assembly is the M3 stainless steel screw, the top sheet, the 15mm brass hex spacer (not pictured), the PCB, the 4mm brass hex spacer, the bottom acrylic sheet and then the M3 stainless steel nut.
The Seeed Studio service allows cutting but does not allow any engraving. This means I can’t put any lettering on the top panel. Or does it? Instead, I opted for a font that can be cut into the acrylic. The key aspect of the font is to avoid areas cut out completely. I looked for fonts on the web. A whole series of fonts were found at this site. Only one of them is free and they all are meant more for looks than the ability to actually cut into acrylic. The supporting bits are too slender for practical use.
So I ended up designing my own font. I usually gave a name to each of my projects. The name for this one is Deccan. The board is an accessory decoder – shortened to accdec. The font is constructed using basic arcs and lines and should be easy to incorporate into any design. I needed only a small subset of letters but I have a rough idea of how all the letters should look like.
I started out by drawing the pattern in a CAD program that I use. The package is TurboCAD – it is a commercial package but an older version is available for free on the web. I have been using this for a very long time and am relatively familiar with it. I fitted two copies of both the top and bottom sheets.
The package allows exporting it in DXF format. Seeed needs it in EPS or CDR format. This is where things got hazy. I tried several different options on the web to convert a DXF into EPS. I checked the EPS in Photoshop but the result was always with one edge being slightly truncated. I added the two L shaped marks outside the area so that the resulting EPS included every part of the graphic. I finally managed to do it but in the fog of war neglected to record the exact steps I used. Later, when I tried to revisit it, I could not get the same results. But at least I had an EPS that I could use.
I placed the order with Seeed studio with the EPS file attached. I got an email saying that it was being processed a couple of days later. Another email 5 days later told me it was shipped. I did get an email saying it is traceable but Australia Post does not let you monitor it once it has entered Australia. I received the order 18 days after I ordered it. The order was for 5 pieces. As I had two copies fitted in a sheet, I had 10 pairs of sheets. Peel off the protective sheets and you have the top and bottom sheets. I assembled the lot using the hardware and here is the finished piece.
No comments:
Post a Comment