Hand-held case/enclosure design using CAD tools

Hello--

I am working on a custom electronics system which ultimately requires a hand-held case design. Consequently, I am wondering if anyone would know of a good book, paper or tutorial on electronics case design.

How would I align the circuit board inside the case with the outside of the case? How do I create standoffs for the circuit board? How do I effectively deal with the routing of wires inside of the case? Perhaps there are more general books that are available on this type of design. Does anyone have a suggestion?

As an aside, I am also curious as to how it might be possible to design an enclosure for an electro-optical system. How would I integrate lenses and an optical system into the enclosure? Are there standard mounting parts for lenses which I can model in a CAD program (and then produce using rapid prototyping), or would I simply purchase "ready-to-order" mounting parts?

I've posted something similar on the comp.cad.pro-engineer newsgroup, but for this posting on sci.electronics.design, I've widened the net to be broader than just using the Pro/Engineer software. I hope that this posting should be interesting to a broader group of individuals.

Are there any resources out there on this type of design? Perhaps this is not of interest to those working in electronics (after all, case design is sometimes more often done by mechanical and industrial engineers), but perhaps there are some "important" books/papers/tutorials on how to do this.

Nicholas

Reply to
Nicholas Kinar
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I doubt you'll find a book our there on this that really covers what you want. It's not really possible, there are an infinite numbers of variations possible and every design has it's own unique set of requirements.

Generally speaking, wiring is not a good thing, and you should try to avoid it if possible. A well designed product will for example (if possible) have just the PCB with PCB mount connectors that align with holes in the case. This is cheaper and more reliable.

Lens systems are pretty much a custom thing. e.g. look at security passive IR sensors and you'll see every design is unique and custom.

The best way to learn this stuff is to take things apart and see how others have done it. Then when it comes time for your own design you can incorporate various ideas into your own case.

Electronics designers who don't for example have good in-house mechnaical CAD designers will often resort to off-the-shelf cases for their products, and these can have have built in PCB stand-off's, front panel windows, battery holders etc. So you pick a suitable case from the countless ones available and then design your PCB and product around that case. This isn't really suited to very high volume manufacture, but is great for low to medium volume production.

Dave.

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Reply to
David L. Jones

I don't know of any (but then I don't think I've ever looked for one...)

Look at commercially-available cases from PacTec, Hammond, Bud and many others - some will have mechanical drawings of their products on their website, which should give you some ideas of how things are normally done.

As for making things on the board match holes in the case, or vice versa, all I can say is to measure carefully. Then carefully measure. Then print the board and panel layout to scale, and see if they fit. Then adjust things till they do fit. Repeat as needed.

It is vital that you actually have the parts you will be using on hand while laying out the board and enclosure.

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Peter Bennett, VE7CEI  
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Reply to
Peter Bennett

Thanks for your response, David!

Ah, I think that you are right. There is a diverse number of products out there.

I've done this once before, but I've found that alignment is sometimes really tricky. I suppose that a few revisions of the PCB might be necessary sometimes.

Agreed. I'll take a look at some similar stuff.

I've done this a few times, and this works really well for most circuits. However, if I need to interface to electro-optical or electro-mechanical components, the design becomes increasingly challenging, especially when the system needs to be ultra-portable. I'm either going to have to use a off-the-shelf case, or I will have to look into developing my own custom design.

Thanks, David.

Reply to
Nicholas Kinar

Peter,

Thank you for your reply!

I suppose that it is best to learn from imitation.

I agree that parts always need to be on hand when doing the layout. I've had a number of interesting experiences when I haven't followed this simple design suggestion. The tricky thing with some through-hole components is that often the part will appear to fit on the 1:1 scale layout, and then it will have to be forcefully pushed on the PCB with a pair of pliers. I've broken one or two parts using this method.

Nicholas

Reply to
Nicholas Kinar

This book is pretty good for injection-molded parts:-

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As is this one:

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There are some others-- although a single 6' shelf will hold most of the decent books on this subject, IMHO.

As others have said, look at existing parts and try to visualize how the mold opens, how each part gets ejected, and the reason for every single detail on the parts. Small differences like inserting a deliberate narrow groove where parts fit together (so things don't have to line up perfectly) can make the difference between a cheap-looking product and a nice-looking one.

You really have to pay a lot of attention to details such as wall thickness, rib height-to-width ratio, material, shrinkage (often several percent, and varies with material, additives, process conditions etc.), draft (VERY important- just about everything has to be slightly angled so it will come out of the mold), and what kind of side action is required to do things like make holes on sides.

One way which doesn't use much material or space is to have part of the mounting boss protrude into the PCB mounting hole, but there are many, many ways. High volume consumer goods often uses snaps, but they have disadvantages.

A boss, preferably with gussets to strengthen it. Design it for a specific type of screw. And put it on the back of the case and/or under label so the shrink marks won't show.

Try to avoid them entirely. Failing that, you can use clips and such like. It may be possible to make the kind you need without involving side action, particularly if you can cover up a hole to the outside with a label or something (eg. another part). A "crossover" (metal from mold halves meet to seal off plastic flow) is generally far preferable to side action (eg. a hydraulically actuated moving core)

You can't possibly acquire the design skills that an experienced mechanical engineer has, plus industrial design skills, plus specific knowledge of plastic part design and manufacturing in just one or two books, or just a month or two of study. Knowing a thing or two about mold design also helps.

Reply to
Spehro Pefhany

Perhaps you can ask these questions as well on a forum about 'solid works' (a popular piece of software for designing housings).

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Reply to
Nico Coesel

That's where todays 3D MCAD features of PCB programs like Altum Designer can be useful:

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(the good stuff starts about half way through) Helps get your PCB/Case design right the first time with more complicated projects. Many case and part/connector suppliers will provide 3D models on their website, so you can just import them and do your clearance/fit checking fairly easily. Hammond are one case supplier that provide 3D models for all their cases for example. Check out an early quick 3D mockup for a new little project I'm working on for example:
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If you want to do your own cases easily then this mod and their software might help:

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Their software is easy enough for non mechanical guys like me to start producing something useful in 5 minutes. Designing your own case that looks good and works well takes skill, time and money though, so I'd exhaust all the off-the-shelf cases first before resorting to that option.

Dave.

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Reply to
David L. Jones

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ext -

Yup, just doing this... again.... take mechanical drawing and electrical drawing, lay on top of one another, place on sunny window, look for errors.

George H.

Reply to
George Herold

Thanks, David!

I had a look at the You Tube video, and Altium Designer makes me very excited. In the past, I've been using Eagle Cad to do most of my design work but it might be time for a change. I'll take a look at Altium and see if it will fit my needs.

I had no idea that you have a blog, David! I think that your project is really neat, and I would like to do something similar to what you have done with the custom case. I've bookmarked your video blog for further reference.

Which MCAD are you using? Does the MCAD interface with Altium? (I am assuming that you are using Altium.) According to the You Tube video, there should be a way to exchange data between the two software packages.

Which manufacturing house is producing your case? What would be the cost of manufacturing? I'm currently situated in Canada, but I think that most product facilities for plastics closest to where I am located are in the United States.

Once again, thanks David.

Nicholas

Yeah,

Reply to
Nicholas Kinar

This seems to have been a rite of passage for all those who work in electronics. It's part of the engineering experience. Maybe we learn something from doing it every time. At least I know that such a process helps to drain printer ink cartridges, but oh well...

Nicholas

Reply to
Nicholas Kinar

Great titles! I absolutely love the covers on these books. Although there is always a word of warning about "judging a book by its cover," I think that these are excellent titles. I'll consider ordering them.

Ah, neat ideas!

I'm creating a hand-held ground-based remote sensing system for determining the physical properties of environmental materials. This requires attaching transducers to the circuit board. The transducers that I have been using in previous prototypes unfortunately require the use of wires. Clips are a good idea. In my previous circuits, I simply left the wires to slop around in the box. This was really not a good idea because I soon found that after the circuit was transported, vibrations would create a big tangled mess.

Sigh, I understand the truth in these words. However, because I am a researcher working in the context of a university to do research and also develop a product, I have a vested interest in also learning about new things. Of course, if I was doing this for a company, then it would make good sense to hire a mechanical engineer with some experience in the field. Moreover, purchasing a few books may provide an enlightening experience, and it will simply give me some interesting summer reading!

Spehro, thank you for this post and for the good book titles. I'll be sure to learn a lot during this summer.

Reply to
Nicholas Kinar

I'll give SolidWorks a try. Thanks, Nico.

Reply to
Nicholas Kinar

Both Solidworks and Altium are $thousands, but if you can afford a mold or three, that probably seems quite cheap. ;-)

Reply to
Spehro Pefhany

If the sensors are outside the case, on cables, I'd put connectors on the cables, and matching PC-mount connectors on the PC board, located so that they can be accessed from outside the case (protruding through the front or rear panel.) There are screw terminal strips that could be mounted on the PC board so that they could be accessed from outside the case, for individual wire connections (but I prefer connectors - once you get things connected correctly, you can disconnect and reconnect the cables without worrying about the correct wire order.)

While it is good to learn new things, don't lose track of the actual job you started on.

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Peter Bennett, VE7CEI  
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Reply to
Peter Bennett

Well, I don't actually use MCAD myself, that's not my area. At work we have mech guys who do the 3D models for us, not sure which package they use. But if the model is available from the manufacturer then it's easy for me to attach this to the component myself.

Yes, it uses the STEP file format. So if your MCAD package supports STEP then you are in business.

It's an off-the-shelf case from Hamond, I just pulled that 3D model from their website. See what I said about the ease of designing products around existing cases! They also so custom mods to their cases (cutout/slots etc) for a fee.

Dave.

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Reply to
David L. Jones

Well, I might be able to request access to a site-licensed SolidWorks installation, so it wouldn't hurt perhaps trying it out for a while.

Concerning the actual production of the case, I may also have access to a rapid prototyping machine (there's such a machine in one of our engineering lab), so I wouldn't think about trying out a very expensive mold until I've learned something about actually working with plastics.

Thanks, Spehro!

Reply to
Nicholas Kinar

Ah, the luxury of having engineers who are competent with mechanical things.

For years, I've used Eagle CAD. I don't think that this software package supports anything remotely related to STEP.

It would be a good idea to simply pull a model and then change some of its aspects. Because I have access to a rapid prototyping machine, this might give me an ability to learn from the model and then make my own version of it.

Thanks, David.

Reply to
Nicholas Kinar

My remote sensing system will be used in an outdoor environment - so I am going to have to ensure that the connectors are waterproofed to prevent rain and snow from getting into the case. This was a problem with some of my earlier prototypes.

In the past, I actually used a case from Hammond plastics and created a circuit board with holes to fit the stand-offs. I cut holes in the case for the USB connector and power jack - but the holes also allowed for rain and snow to enter the case. This caused the circuit to malfunction. I thought at first that if the circuit is hand-held, there should be a good possibility of keeping the circuit dry, but the weather thought otherwise. :)

I don't know if this is a logical idea, but my initial thought was to produce an electronics case which also incorporated the transducers. So the transducers would fit into a recess at the front of the case, and the case would be designed to have a trigger grip.

I need to also produce a stationary version of the remote sensing system. The system will be interfaced to a datalogger and then left out in a location which is exposed to the elements.

I think that perhaps the circuit could be placed into an off-the-shelf case, and then the transducers could be placed into a "cradle" designed using mechanical CAD software and produced using rapid-prototyping technology. Connectors on the outside of the case will be used to interface the transducers to the circuit.

Yes, that is true. I might be able to request access to a site-licensed version of SolidWorks, and in addition, there is a rapid-prototyping machine in one of our labs. My initial idea was to learn some of the basics of how to use SolidWorks and then produce an electronics case on the rapid-prototyping machine. I suppose that the more toys you might have access to, the more likely it is to get carried away.

Of course, my first concern is the design and operation of the circuit, as it should always be.

Thanks, Peter.

:)

Reply to
Nicholas Kinar

I your company has such a machine, chances are they have a license for Solid Works as well.

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Failure does not prove something is impossible, failure simply
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Reply to
Nico Coesel

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