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Before becoming an amateur electrical engineer, I was always amazed at seeing EEs leave their motherboards and circuits lying around on desks and in piles, exposed and unprotected. However, today I can appreciate the amount of work it takes to machine a custom box with screw holes, button holes, and connector/display punchouts.
Usually, I just toss a circuit board into an uncut storage box (such as those colored plastic boxes for school supplies). That being said, a custom case provides a more professional appearance and protects the circuit during usage and in storage.
The electronic counter project case begins with a light-gray Velleman box made from ABS plastic. It can be purchased from BGMicro for $3.10, part #ACSG1098. The size is 5.3″ x 3.0″ with a 2.0″ depth.
Velleman G1098 ABS plastic project boxes.
This Velleman box is nice because:
I cannot begin to express the value of a flat-sided box for machining purposes. Just look at what acrobatics I had to go through to machine a tapered box for another project.
Machining the side of a black tapered project box by using a custom adapter plate, clamps, 90-degree angle plate, and vise.
In order to machine a tapered (angled or curved) project box, I had to create a custom adapter plate from a thick piece of plastic (light blue in the above photographs). The project box screwed onto the adapter plate using the same holes as the project box cover. The adapter plate clamps onto a right angle plate (90 degree) that sits in the machine vise.
Of course, the straight sides on the Velleman box don’t entirely rule out the value of making an adapter plate. The ABS plastic is soft enough that it bends and scratches in the vise. I used a swatch of rubber cloth between the vise and the box to avoid scratches, and I machined slowly and carefully to avoid the box pulling out of the vise. However, if I were producing multiple boxes, I’d make an adapter plate that the project box could be securely screwed onto.
The counter project box was machined on a mini-mill/drill with a homemade digital readout (DRO). All of the holes and slots are first laid out on a computer drawing. Then, the coordinates of each hole are typed onto the drawing using the rulers built into the drawing program. So, machining is as simple as moving to each point on the paper print out and drilling/machining. (See Wall plate machining for an in-depth example.)
The motherboard and power board are attached to the project box with screws that fit into holes that need to be drilled and tapped. But, the Velleman project box has feature that can eliminate this extra work -- if you design your boards for the box.
The sides of the Velleman box include slots for inserting multiple PCBs horizontally or vertically. These slots also probably increase the rigidity of the side panels without using an entire solid piece of thicker plastic.
A Dremel rotary tool and grinding stone remove the bottom portion of project box slots to fit a PCB that lies flat.
Unfortunately for me, I failed to take into account the thickness of the slots before calculating the coordinates for the motherboard and power board PCB holes. I had to grind off the bottom of several slots to fit the circuit boards.
Furthermore, these slots also interfered with the power switch fitting flush and tight against the side of the box. The tops of a slot had to be ground off in order to give the power switch nut a large enough surface area to grab onto.
I suppose with a little planning that these slots might be helpful. But, for me, they were just a pain.
The switches, buttons, and terminal block connectors are labeled with clear adhesive stickers printed out on a color laser printer. I used Avery Full Sheet Labels for Ink Jets (#8665) because the store didn’t have a version for laser printers.
Although the labels turned out okay, the finish is a somewhat matte and the toner tends to rub off. The toner problem may be due to these labels only being appropriate for ink jet printers.
I made the mistake of cutting the labels out with scissors rather than a straight paper trimmer. So, the edges are a bit wavy.
Oops! A not-quite square sticker and a poorly-cut power-plug hole.
Because the power board PCB was the last item to be manufactured, the rest of the box had already been machined before the exact location of the power outlet plug receptacle was known.
When the power board arrived, I decided to be lazy and cut out the hole with a Dremel, rather than struggling to align the power-plug receptacle and project box on the milling machine vise. After all of my hard work in cutting perfect holes, why did I rush the last hole? Oh, well.
Since the power-plug receptacle is functional, it doesn’t make sense to go back and machine a replacement box. However, the power receptacle’s ugliness needs covering up.
Left: A hole punch makes a nearly clean hole in a clear adhesive sticker. Right: The sticker is applied using the power plug as an alignment tool.
A sticker patch was printed out with an alignment crosshair for the power plug-hole. Fortuitously, a standard hole punch produces the correct size hole. But, sadly, the crude low-cost hole punch isn’t very sharp and didn’t cut cleanly on one side -- resulting in a slight crimp of the label.
Nevertheless, even a marginally crumpled hole sticker is better than the jagged gash made in the project box with the Dremel. Using a power plug as a guide, on goes the sticker!
Side view of the BroMatic 2000 electronic counter showing the power plug receptacle and power switch.
It looks acceptable. In fact, when the device is plugged in, the coarse edge made by the hole-punch isn’t visible.
Although I’m generally pleased with the sticker labels, I need to find clearer versions that also retain laser toner better. I also need to cut the labels using a cutting board. Lastly, there needs to be a consistent method of placing the stickers on straight (rather the slightly crooked) as they don’t peel off easily.
Now it is time to explore the various screens and options available of the electronic counter.