Author Topic: Project Design guide / thought process  (Read 4719 times)

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Offline Tomasreabe

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Project Design guide / thought process
« on: September 14, 2010, 01:56:41 pm »
On the last live blog you were making comments about beginner guide blogs to get views. I would think that you could do quite well with these. I would ask for one on cost effective design.

So just as an outline:
What are the major costs in an electronic design, (pcb, components, manufacturing where should one be looking to make sure you will have a quality cost effective part)
Should you aim for a single sided design or 2 sided,  (should all the parts be on one side of the board? what is a valid reason to make a 2 sided board?)
2 layer or 4 layer board with closer packed components, ( what is a valid reason to step up to a 4 layer board)
Jelly bean parts to include in your design or why not to use jelly bean parts, (a list of good jelly bean parts)
Things to include for trouble shooting the design, Test ports/headers for probing the circuit, (or other things that a new person might overlook)


If you put together a good guide / tutorial then we can link to it in sparkfun.com forums I think that would be a good community to get in on what is happening over here.
 

Offline Jon Chandler

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Re: Project Design guide / thought process
« Reply #1 on: September 14, 2010, 05:51:38 pm »
Just one comment....

For a product that will eventually be sold to the public, the functionality is of course key, and a reliable circuit design that can be built is essential but the first major step after the concept is to figure out the packaging,  If you're making thousands and you have the budget, making an enclosure is no big deal.  If the market is small and the budget limited, the enclosure becomes critical.  An off-the-shelf enclosure may work well, but long lead times, machining costs for small quantities and other factors can really complicate the process.  Even when using an off-the-shelf enclosure that you'll have machined locally, supply is a major concern.  Lead times of weeks are not uncommon, leading to massive panic when that big order finally arrives but you can't get the parts for a timely delivery.

The enclosure is going to drive a great number of design issues.  The printed circuit board size and shape and the location of controls and connectors is controlled by the enclosure.  Whether to use a single or double sided board is a function of board size so is a function of the enclosure.  Mounting holes and clearance around bosses in the enclosure control the board design.

The enclosure has impacts even beyond these.  The size and type of batteries is limited by the enclosure, so this feeds back into the circuit design - what voltage and how much current is available and etc.  The enclosure may even dictate the display technology, size and format.

In some ways, you need to start at the end and work back towards the middle or beginning :)


Jon


 

Offline DJPhil

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Re: Project Design guide / thought process
« Reply #2 on: September 14, 2010, 09:41:31 pm »
On the last live blog you were making comments about beginner guide blogs to get views. I would think that you could do quite well with these. I would ask for one on cost effective design.

May your wish be partly to mostly granted.

I figure your intent is to hear from Dave, but I'll throw in my two nH about the remainder. I'm a noob still, but it is a forum after all!
What are the major costs in an electronic design, (pcb, components, manufacturing where should one be looking to make sure you will have a quality cost effective part)
In my limited experience, from a one-off to low production hobbyist perspective, most of the cost is in UI and enclosure. Take the typical guitar pedal or amplifier as an example. The pots, jacks, switches, and case make up the vast majority of the cost. This assumes a good deal though, for example, that you're doing the boards yourself and not including start up costs. The electronic parts themselves tend to be the cheapest budget category, though it depends on what you're doing. This is mostly from my limited analog perspective, but I definitely understand why most kit manufacturers sell just a board, or a board plus parts.
Should you aim for a single sided design or 2 sided,  (should all the parts be on one side of the board? what is a valid reason to make a 2 sided board?) 2 layer or 4 layer board with closer packed components, ( what is a valid reason to step up to a 4 layer board)
I think these decisions revolve mainly around noise performance, intended size, and ease of manufacture. Low level or high speed signals will require attention to grounding (see other related threads) that's much more easily accomplished with multilayer boards. If you need to fit a particular space, and it's small, multiple layers will help you pack things in tightly, which also helps with noise. If you're etching your own boards you're obviously limited in your options. I've read that keeping components on one side of a two sided board makes automated manufacture much easier.

Jelly bean parts to include in your design or why not to use jelly bean parts, (a list of good jelly bean parts)
There's been a few good threads on jellybean parts with at least one list, a quick search should turn up a few. We should really get a sticky going.

Things to include for trouble shooting the design, Test ports/headers for probing the circuit, (or other things that a new person might overlook)
Good call on this one, it's hard to think of everything. :)

Sorry if this seems a bit cut short, I've got to go at the moment, someone's stopped to visit.
 

Offline osmosis321

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Re: Project Design guide / thought process
« Reply #3 on: September 22, 2010, 03:50:20 pm »
The enclosure has impacts even beyond these.  The size and type of batteries is limited by the enclosure, so this feeds back into the circuit design - what voltage and how much current is available and etc.  The enclosure may even dictate the display technology, size and format.

Hmm in my limited experience the opposite is true:  the enclosure is the last thing designed, and it's dimensions are subordinate to the circuit.  One does not design a circuit so that it fits into a particular box, one designs a box that effectively houses a circuit.

Yes, the board design has the end product, enclosure and all, factored into it, but to start your design from the enclosure and work from there to the functioning parts is the tail wagging the dog.


- osmosis
 

Online Mechatrommer

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Re: Project Design guide / thought process
« Reply #4 on: September 22, 2010, 04:02:58 pm »
The enclosure has impacts even beyond these.  The size and type of batteries is limited by the enclosure, so this feeds back into the circuit design - what voltage and how much current is available and etc.  The enclosure may even dictate the display technology, size and format.

Hmm in my limited experience the opposite is true:  the enclosure is the last thing designed, and it's dimensions are subordinate to the circuit.  One does not design a circuit so that it fits into a particular box, one designs a box that effectively houses a circuit.

Yes, the board design has the end product, enclosure and all, factored into it, but to start your design from the enclosure and work from there to the functioning parts is the tail wagging the dog.


- osmosis

then you should rename yourself, reverse osmosis :D kidding. your statement maybe true if your end product is the PCB itself, but naturaly, its the housing that the end customers will get to hold to, too big or too small or too weirdly shaped will make it less friendly. so you must comply to a friendly shape housing (visible product) first before doing anything else. think ergonomics!
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Offline Bored@Work

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Re: Project Design guide / thought process
« Reply #5 on: September 22, 2010, 06:03:21 pm »
One does not design a circuit so that it fits into a particular box, one designs a box that effectively houses a circuit.

Your claim is easy to debunk. Every PC motherboard PCB is exactly designed so it fits in a particular box.
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Offline RayJones

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Re: Project Design guide / thought process
« Reply #6 on: September 22, 2010, 07:37:27 pm »
Definitely the enclosure should be thought about early in the design process.

Nothing more frustrating that having your u-beaut circuit all soldered up then not being able to find a box, especially if all the boxes are just a smidge too small.

And yes numerous products, especially in the specialist area, must fit a particular form factor, dictated by the enclosure design.
 

Offline Jon Chandler

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Re: Project Design guide / thought process
« Reply #7 on: September 22, 2010, 10:37:34 pm »
I wish I could claim this was the result of excellent planning, but honestly it was a lucky find.  But you can be sure that if I design something else of a similar size, it won't be an accident that it fits this enclosure.




 

Offline osmosis321

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Re: Project Design guide / thought process
« Reply #8 on: September 23, 2010, 06:02:14 pm »
Your claim is easy to debunk. Every PC motherboard PCB is exactly designed so it fits in a particular box.

Methinks that's a different situation.  The PC MB manufacturers are made to use those form factors by way of market forces and industry standards.  They may be designed to fit a particular box, but only out of economic necessity, not technical necessity.

They don't design the enclosures, and therefore cannot design the enclosures to fit their boards.  Their situation is reversed.
 

Online Mechatrommer

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Re: Project Design guide / thought process
« Reply #9 on: September 23, 2010, 06:23:43 pm »
for this kind of product (below), which one comes first, the housing? or the circuit?
http://a.img-dpreview.com/reviews/CanonEOS5DMarkII/Images/specsview.jpg
« Last Edit: September 23, 2010, 06:25:55 pm by shafri »
It's extremely difficult to start life.. one features of nature.. physical laws are mathematical theory of great beauty... You may wonder Why? our knowledge shows that nature is so constructed. We simply have to accept it. One could describe the situation by saying that... (Paul Dirac)
 

Offline Jon Chandler

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Re: Project Design guide / thought process
« Reply #10 on: September 23, 2010, 06:56:27 pm »
Depending on budget, an enclosure can be made to order.  Spending thousands of dollars on tooling and purchasing thousands or even tens-of-thousands of enclosures can make the unit cost reasonable.  But for those of us working with small quantities, an off-the-shelf enclosure is far more practical.  If you want something at all stylish, say a handheld enclosure, the circuit boards are going to have to be designed to fit.

Here's an alternative I made when I found the local hackerspace had a laser cutter.  I won't tell you how much it cost to cut all the layers!




I think this link to more pics will work.  The LEDs behind the layers of acrylic make an interesting effect.  Looks like a bargraph instead of single LEDs.


Jon
 
 

Offline osmosis321

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Re: Project Design guide / thought process
« Reply #11 on: September 24, 2010, 02:05:49 am »
Here's an alternative I made when I found the local hackerspace had a laser cutter.  I won't tell you how much it cost to cut all the layers!




I think this link to more pics will work.  The LEDs behind the layers of acrylic make an interesting effect.  Looks like a bargraph instead of single LEDs


hey... HEY!

Thats a truly wicked idea I never had before.  What wattage laser made that?  I ask because there's a guy within walking distance of my home/shop with a 45 watt laser and I've done business with him before. I've treated him very well and I'm sure he'd give me a good deal on work like that, assuming he's capable of it
 

Offline EEVblog

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Re: Project Design guide / thought process
« Reply #12 on: September 24, 2010, 03:13:22 am »
The enclosure has impacts even beyond these.  The size and type of batteries is limited by the enclosure, so this feeds back into the circuit design - what voltage and how much current is available and etc.  The enclosure may even dictate the display technology, size and format.

Hmm in my limited experience the opposite is true:  the enclosure is the last thing designed, and it's dimensions are subordinate to the circuit.  One does not design a circuit so that it fits into a particular box, one designs a box that effectively houses a circuit.

Yes, the board design has the end product, enclosure and all, factored into it, but to start your design from the enclosure and work from there to the functioning parts is the tail wagging the dog.

As usual, yes and no.
I've mentioned on the blog before that the choice of enclosure (and user interface) can be critical and should often be the first decision. This is especially true for low to medium volume niche products, particularly one that you intend to fund and/or build supply yourself. e.g an open source hardware project.

You could design the worlds most clever circuit, but then find that the custom enclosure blows out your budget enough to make the product unmarketable.

But of course the opposite could be true depending upon the product and the market. But all things considered,  the case should be far from the last thing designed.

Many of my own projects are designed from the enclosure backwards. Electronics magazine projects are a classic a example of this. A poor magazine project will involve the concept you describe of designing the circuit and function first, and then doing the box last. The end result is a great circuit but built into a really shitting looking and expensive box with shitty looking wiring running everywhere. A great project on the other hand will be well designed around an existing off-the-shelf box and make clever use of the chosen box design.

Dave.
 

Offline Jon Chandler

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Re: Project Design guide / thought process
« Reply #13 on: September 24, 2010, 07:14:46 am »
The laser cutter used was a 50w CO2 according to the webpage at Metrix CreateSpace in downtown Seattle.  They opened maybe a year ago and it's an interesting concept.  Instead of being located in some industrial area, it's in a popular urban area.  They are open from noon until midnight, mirroring some of the vibe of the neighborhood.

A large part of their focus seems to be MakerBots.  The main function of MakerBots seems to be making MakerBot parts! <g>  Start with a crude design, then make better parts....and the better parts let you make even better parts!  I haven't seen too many things build using one that make me want to try it.

The hardest part of the laser-cut enclosure was keeping all the layers straight.  Each layer is 1/8" thick acrylic - I needed 8 layers to get the height I needed plus the top and bottom layers.  A more practical alternative is to use a top and bottom layer, with the circuit board held between them with spacers.  The enclosure in the picture cost over $30 just for cutting, not including materials.  Not too practical but it does have some "oh wow" potential, and it was a good introduction to laser cutting.


Jon
 

Offline DavidDLC

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Re: Project Design guide / thought process
« Reply #14 on: September 24, 2010, 05:39:48 pm »
Acrylic laser cut enclosures are getting popular. I love those.

We have a $20K Laser cutter here in our lab (at work), but I don't want to use it for personal projects.
 

Offline Neilm

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Re: Project Design guide / thought process
« Reply #15 on: September 25, 2010, 01:40:34 pm »
If you are doing it to be sold, I always find that you decide the UI first. That then gives you a solid starting block. Part of that decision is the enclosure you want to use. Then rough design the electronics, figure out how much room they are going to take and what layout would be required to give good EMC performace etc and go round the loop again with the extra info. It may mean you have to accept less funcitonality or a larger box. If it is just for yourself, go ahead and get on with it - the only person you will annoy with a poor UI is you.

Of course, if you are wanting it to be sold then you have to be aware of what regulations it will have to meet. Some of those will impact decisions you will make. For example if you are designing a CAT IV multimeter you don't want the terminals to be 4mm apart.

The choice between 2, 4, 6, 8, 10 layers depends on the complexity of what you are designing and what EMC regulations you have to meet. It is much easier to design something that is immune to EMC with a multilayer board and careful layouts. Note that this HAS to be considered at the start of the project. Trying to "bolt it on" at the end is a good way of being very late and having to completly rework almost everything.

Neil
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