This article describes my first serious effort to design a plastic enclosure for an electronics project using CAD.
When I built a 3D printer, one of my motivations was to be able to fabricate a plastic enclosure for a DIY project. My signal generator project would be best served in a metal (shielded) enclosure. But I have never been much for metal work. Since the signal generator power levels are quite low, I thought I would just design and print a plastic enclosure.
My previous article described the components used in the signal generator project. These are an Arduino micro-controller, an AD9850 direct digital synthesizer module, a rotary encoder and an LCD display with keypad. These can fit easily into a plastic enclosure with a bit of planning.
On the above left you can see the design of a plastic enclosure, really the base of a small box. Later, I will add a top cover. On the above right, you can see the base with the Arduino and printed circuit board fitted inside. All of this is produced using a CAD or computer aided design application.
When you are doing this kind of design for a plastic enclosure, it is very useful to also have 3D models of the parts that will go into the enclosure. I was able to find a ready-made 3D model for the Arduino UNO previously posted by the GrabCAD Community. Once I had designed my printed circuit board, a created a simple 3D model of it, as well.
As you can see at the right above, I was able to assemble the base, Arduino and PCB models together to make sure that everything fits, that the holes are in the right place, and so on. The LCD Keypad will mate on top of the Arduino, but I have not found a model for that yet. Eventually, when I design the top of the plastic enclosure, it will have cut-outs for buttons and the LCD display, as well as the rotary encoder. But first, I will build and assemble the bottom half.
Plastic Enclosure Design with CAD
Following are the steps I used in designing the plastic enclosure with a CAD program. For simplicity, I have converted all measurements to metric.
- Using a rough sketch on paper, I decided that I would need a base 150 mm long, 100 mm wide and 38 mm high. The thickness of the plastic enclosure side walls, bottom and top will be 4 mm. This will enable me to hold the top and bottom together with four 6-32 screws and acorn nuts at the bottom, which will also provide feet for the plastic enclosure.
- Using CAD, I created block and then removed the interior to create the base, rounding the edges.
- The Arduino will be mounted on four posts on the left side of the base. Each of these posts has a 2 mm diameter extrusion at the top. These will mate with the four holes in the Arduino board. The nice thing about CAD is that you can move these posts around and fine tune their placement to fit the Arduino.
- Once the Arduino model was fitting snugly on its posts in CAD, I was able to cut holes in the side wall on the left of the right sizes for the USB and power connectors. Creating these holes in CAD is as simple as sketching them and then using the “extrude” function to carve out the material in the right places.
- Similarly, I used my printed circuit board model to place supports and a screw mounting hole for the PCB on the right side of the base.
- Finally, the two round holes on the back wall of the base are for the signal generator signal output using BNC connectors.
Next, I will print the plastic enclosure base and get everything wired up.
Two final notes. First, the signal level from the AD9850 module is less than 1V peak-to-peak. Later, I may want to add a small signal amplifier, so I have left extra space in the case for such an event. Second, I fell back to using the Arduino UNO rather than the larger MEGA. I thought I needed the extra digital I/O pins provided by the MEGA. But then I discovered that the Arduino UNO’s analog input pins could also be used for digital output.