Alternate SOB size case design

Standard PCB templates and project cases

Re: Alternate SOB size case design

Postby dsm » Sat Feb 04, 2012 3:21 pm

DP6037-open-case-dsm-v1

The DP6037-open-case-dsm-v1 design the following features:
  • Top and bottom clear acrylic windows like the frame-extrusion-case-dsm-v1 case design (above).
  • Magnetic fastening scheme like the Bus Pirate v4fd case design (see yabp case forum thread).
  • Parametric design to rapidly produce multiple custom variants.
  • Uses cheap 1.5 mm acrylic for parts to be customized (via laser cutting).
  • Top and bottom acrylic are the same overall size as the DP6037 board (only with 0.5 mm corner radius).
  • Minimizes the amount of relatively expensive SLS nylon material.
  • Top and bottom acrylic windows and printed circuit board resist diagonal deformation forces.
  • Allows case variants with acrylic end windows for electro-optical components.
DP6037-open-case-assembled-dsm-v1-perspective.jpg
DP6037-open-case-assembled-dsm-v1 (perspective)
Notice interference between ExtPwr connector and case.

Thanks for your time.

dsm
Last edited by dsm on Sun Feb 05, 2012 6:36 pm, edited 3 times in total.
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Re: Alternate SOB size case design

Postby ian » Sun Feb 05, 2012 6:20 am

Thanks dsm,

I also got these board tests in the mail this week. Are we sticking with 2.0mm edge keep out, or are we going with 1.7 as mentioned previously? I thought 1.7, but maybe IR Toy is still set to 2.
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Re: Alternate SOB size case design

Postby dsm » Sun Feb 05, 2012 6:02 pm

board edge component keepout

My recommendation was for a 1.7 mm board edge component keepout based on the following error budget calculation...
    1.0 mm deep slot +
    0.2 mm case-to-board (3D SLS printer) error budget +
    0.2 mm board-edge-position (board routing) error budget +
    0.1 mm component-placement (pick-N-place) error budget +
    0.2 mm component-to-case margin (so SMT components don't touch the case)
    = 1.7 mm
As a practical matter, a 1.7 mm board edge component keepout would allow ordinary 0.1" (2.54 mm) wide headers to be placed 3.0 mm from the edge of the board. 1.7 mm + 1.27 mm == 2.97 mm => 3.0 mm (on a 0.5 mm placement grid).

I mentioned changing the board edge component keepout from 2.0 mm to 1.7 mm to vimark.
In the 03Feb12 USBIRtoy layout, this feature appears to have been implemented for the USBIRtoy design.
I am assuming that vimark has been propagating these changes to all Dangerous Prototypes board templates.



My comments on the bottom of page one of this forum thread had to do with the layout of the Bus Pirate v3.5e and Bus Pirate v4c boards. Since these board designs were updated before some specifications for the new Dangerous Prototypes board templates were proposed, some issues may remain.

Even with a 1.7 mm wide board edge component keepout, several components in these layouts violate this specification...
  • LEDS (4x) ~ 1.2 mm wide 0805 LEDs (aka 2012) should be 2.5 mm from the board edge (currently 2.0 mm).
    1.7 mm + 0.6 mm == 2.3 mm => 2.5 mm.
  • push-buttons (2x) ~ 5.2 mm wide push-buttons should be 4.5 mm from the board edge (currently 3.5 mm).
    1.7 mm + 2.6 mm == 4.3 mm => 4.5 mm.
  • ExtPwr (1x) ~ 2.54 mm wide male header should be 3.0 mm from the board edge (currently 2.0 mm).
    1.7 mm + 1.27 mm == 2.97 mm => 3.0 mm.
Thanks for your time.

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Re: Alternate SOB size case design

Postby dsm » Mon Feb 13, 2012 4:23 am

board edge component keepout

ian,

Have you decided about whether the Bus Pirate v3.5e and Bus Pirate v4c layouts need to be updated as described above?
The reason I ask is that some the board edge alternate SOB case designs (which might be the best choice for Bus Pirate v4c)
are only possible if the "board edge component keepout" areas are clear.

Thanks for your time.

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Re: Alternate SOB size case design

Postby ian » Mon Feb 13, 2012 4:30 am

Yes, we will need to do that. Look for the updates later today.
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Re: Alternate SOB size case design

Postby dsm » Thu Feb 16, 2012 12:11 am

DP6037-open-case-dsm-v1 images

The DP6037-open-case-dsm-v1 prototype case parts ordered 04Feb2012 from Shapeways arrived back on 14Feb2012.
See (link) for more details on this design.

IMG_0782_2.jpg
DP6037-open-case-dsm-v1 enclosure
U-shaped main case part and USB end case part
acrylic top and bottom windows

Case Assembly Procedure
  • Use an ordinary wooden toothpick to make sure any loose nylon powder left over from the Shapeways SLS 3D
    printing process is removed from the magnet wells in the U-shaped main case part and the USB end case part.
    The reason for this step is to make sure that the magnets seat as deeply as possible in the magnet wells.
    ----------
  • Press a 3.0 mm diameter by 3.0 mm long neodymium magnet into the left-hand magnet well
    of the USB end case part (when viewed from the inside with the USB opening toward the top)
    with the "north" pole of the magnet facing out of the magnet well.
    Use a small drop of cyanoacrylate (aka super glue) to hold the magnet in position if the magnet well is loose.
  • Press a 3.0 mm diameter by 3.0 mm long neodymium magnet into the right-hand magnet well
    of the USB end case part (when viewed from the inside with the USB opening toward the top)
    with the "south" pole of the magnet facing out of the magnet well.
    Use a small drop of cyanoacrylate (aka super glue) to hold the magnet in position if the magnet well is loose.
  • Press a 3.0 mm diameter by 3.0 mm long neodymium magnet into the left-hand magnet well
    of the U-shaped main case part (when viewed from the inside with top side up)
    with the "north" pole of the magnet facing out of the magnet well.
    Use a small drop of cyanoacrylate (aka super glue) to hold the magnet in position if the magnet well is loose.
  • Press a 3.0 mm diameter by 3.0 mm long neodymium magnet into the right-hand magnet well
    of the U-shaped main case part (when viewed from the inside with top side up)
    with the "south" pole of the magnet facing out of the magnet well.
    Use a small drop of cyanoacrylate (aka super glue) to hold the magnet in position if the magnet well is loose.
    ----------
  • Slightly chamfer the top and bottom acrylic windows using 400 grit sandpaper.
    The reason for this step is to remove the slightly raised edge that the that laser-cutting process sometimes leaves.
  • Place the IO connector opening in the top acrylic window over the IO connector on Bus Pirate v4c board
    so that the opening is centered on the connector. Slide this combined assembly into the U-shaped main case part.
    Note that the U-shaped main case part can be slightly bent to avoid board components (because it is made of nylon).
  • Slide the bottom acrylic window into the bottom slot in the U-shaped main case part.
  • Attach the USB end case part to the open end of the U-shaped main case part using the neodymium magnets.
Comments
  • The orientation of the magnets is intended to make sure that (a) the U-shaped main case part and USB end case part can't be assembled wrong and (b) to allow case parts from different production runs to be assembled correctly.
  • The neodymium magnets are sufficiently strong that you can determine the "north" [1] and "south" [2] poles of the magnets by just letting the individual magnets roll around on a smooth table.
  • The prototype DP6037-sized Bus Pirate boards [3] were larger than expected.
    The prototype Bus Pirate v3.5e board was actually 60.2 mm by 37.3 mm.
    The prototype Bus Pirate v4c board was actually 60.15 mm by 37.25 mm.
  • These dimensions are toward the upper end of the range that this case was designed to accommodate.
    The result is a small gap at the corner that disappears if the prototype Bus Pirate board is removed
    and top and bottom acrylic windows are still present.
  • Is this a systematic problem with Seeed Studio Fusion PCB Service boards?

IMG_0787_2.jpg
assembled DP6037-open-case-dsm-v1 enclosure ~ top view

IMG_0786_2.jpg
assembled DP6037-open-case-dsm-v1 enclosure ~ bottom view

Thanks for your time.

dsm

[1] "north" pole refers to the end of the magnet that is attracted to the earth's north magnetic pole.
[2] "south" pole refers to the end of the magnet that is attracted to the earth's south magnetic pole.
[3] The the DP6037-size Bus Pirate boards shown in the images are prototypes since some components
on the boards violate the board edge component keepout specification.
Last edited by dsm on Mon Feb 20, 2012 2:07 am, edited 1 time in total.
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Re: Alternate SOB size case design

Postby dsm » Sun Feb 19, 2012 12:59 am

modular open case design

Instead of using a U-shaped main case part and USB end case part to build an enclosure as shown in the previous posting, one could use four individual modular side walls. In both cases, the enclosures would be held together with neodymium magnets. In both cases, the top and bottom laser-cut acrylic windows would be the same size as the main board for easy customization. The top and bottom laser-cut acrylic windows also keep the enclosure from "racking".

Assume for the moment that these modular side walls can be generated parametrically by changing one length related parameter. Dimensions are nominal - actual dimensions include wall thickness adjusted for slot depth and a 0.4 mm board-to-case margin. Cases for all proposed Dangerous Prototypes board sizes could be constructed from the following modular side walls
(plus variants with a USB connector opening)...
    50 mm modular-side-wall
    60 mm modular-side-wall
    70 mm modular-side-wall
    80 mm modular-side-wall
    90 mm modular-side-wall
    100 mm modular-side-wall
    +
    31 mm modular-side-wall
    37 mm modular-side-wall
    43 mm modular-side-wall
    49 mm modular-side-wall
    56 mm modular-side-wall
    62 mm modular-side-wall
modular-open-case-parametric-sides-dsm-v2-family-perspective.jpg
modular-open-case-side-walls-dsm-v2 ~ family ~ perspective

modular-open-case-parametric-USB-sides-dsm-v2-family-perspective.jpg
modular-open-case-USB-side-walls-dsm-v2 ~ family ~ perspective

For example, a DP6037-size case would require the following components...
    1x ~ 37 mm modular-usb-side-wall
    2x ~ 60 mm modular-side-wall
    1x ~ 37 mm modular-side-wall
    8x ~ 3.0 mm diameter by 3.0 mm long neodymium magnets
    2x ~ 60 mm by 37 mm by 1.5 mm acrylic windows
Ignoring the Shapeways handling fee for a moment,
    The laser-sintered nylon components in white for a DP6037-size case would be roughly $7.62.
    The laser-sintered nylon components in white for a DP10062-size case would be roughly $12.50.
DP6037-modular-open-case-assembled-dsm-v2-perspective.jpg
DP6037-modular-open-case-assembled-dsm-v2 ~ perspective

DP6037-modular-open-case-assembled-dsm-v2-top-view-perspective.jpg
DP6037-modular-open-case-assembled-dsm-v2 ~ top view ~ perspective

DP6037-modular-open-case-components-dsm-v2-perspective.jpg
DP6037-modular-open-case-components-dsm-v2 ~ perspective

Thanks for your time.

dsm
Last edited by dsm on Sun Feb 19, 2012 7:10 pm, edited 1 time in total.
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Re: Alternate SOB size case design

Postby ian » Sun Feb 19, 2012 6:35 pm

Hi dsm,

Glad the PCB arrived quickly. I'm out of town at the moment, but I have this bookmarked for more attention when I get back. The designs look really great.

The prototype DP6037-sized Bus Pirate boards [3] were larger than expected.
The prototype Bus Pirate v3.5e board was actually 60.2 mm by 37.3 mm.
The prototype Bus Pirate v4c board was actually 60.15 mm by 37.25 mm.


I was going to ask if you thought this tolerance, or something we did. Given that the boards use same template and have different specs, I guess it is an issue with the super cheap prototype PCBs from fusion?
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Re: Alternate SOB size case design

Postby tayken » Sun Feb 19, 2012 11:48 pm

I measured the board sized too, they are close to dsm's findings (usually, the 2nd decimal point is different. :) I'd say tolerance of manufacturer. They are using routers for cutting down PCBs, sub-mm accuracy is not needed for this.
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Re: Alternate SOB size case design

Postby dsm » Mon Feb 20, 2012 2:05 am

board dimension tolerance

ian,

Without knowing more about the workflow for the Seeed Studio Fusion PCB Service, it is difficult to determine how serious the problem might be. More data is needed. Given that you deal with more Seeed Studio Fusion PCB Service boards than most people, maybe you could measure a few boards when you get back home and get a feeling for whether this board size discrepancy issue is real or not. The Seeed Studio Fusion PCB Service site tends to list nominal capabilities and not tolerances. There are are a number of sources of error that could creep into their process such as
    CAD data round-off errors
    router path conversion errors
    board positioning hole diameter tolerance (mechanical) ~ 0.08 mm
    feature registration (mechanical) ~ 0.09 mm
    tooling positioning errors
    router bit wear errors
    ...
The board edges are a bit rough which makes me suspect router bit wear. The amount of discrepancy we're talking about is only about 10 mils. Removing this amount of material to bring the board into compliance with what is expected using 400 grit sandpaper and a palm sander would be no problem if it were not for the USB connector hanging over the edge (which is a good feature in order to maximize USB engagement margins for typical wall thicknesses). People just need to be aware that there may be a board size tolerance. In most situations, that won't be a problem.

I don't think the source of the problem is anything that Dangerous Prototypes may have done.
I do think this issue may just be a side effect of using a very cost effective board fabricator in a very competitive market.
The Seeed Studio Fusion PCB Service may not even know that they have a problem.
Board fabricators are often not very introspective about the limits of their process.

Thanks for your time.

dsm
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Re: Alternate SOB size case design

Postby ian » Fri Feb 24, 2012 3:53 am

Ok, it sounds like the tolerances will be something we can deal with. We can add a recommended board tolerance/keepout to our suggestions for case designers.

Other notes for case designers (added to main thread)
-we see PCB widths vary up to +0.4mm, and recommend you design for up to +0.4mm of extra PCB in both directions.
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Re: Alternate SOB size case design

Postby dsm » Wed Feb 29, 2012 4:27 am

comments

Maybe a board size tolerance specification along the lines of +0.2 mm -0.3 mm would be more useful for Seeed Studio.
An asymmetric board size tolerance specification with a tighter oversize tolerance would signal which way you want them to react.
Allowing Seeed Studio to be oversize by up to 0.4 mm on a simple routed edge board probably sends the wrong message.
0.4 mm (roughly 16 mils) is huge in this context.

Does Seeed Studio have an internal board size tolerance specification that they are willing to share with you?

Thanks for your time.

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Re: Alternate SOB size case design

Postby dsm » Mon Mar 19, 2012 2:47 pm

Raspberry Pi cases

If you have a moment, check out
Thanks for your time.

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Re: Alternate SOB size case design

Postby ian » Mon Mar 26, 2012 12:35 pm

I will check out the tolerance, they are usually forthcoming if I ask :)

Wow, there is just a plethora of cases for the Raspberry pi!
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Re: Alternate SOB size case design

Postby dsm » Tue Mar 27, 2012 4:14 am

Raspberry Pi dimensions

ian wrote:Wow, there is just a plethora of cases for the Raspberry pi!

Which is kinda interesting in that, despite what the Raspberry Pi website faq (link) states, there seems to be considerable uncertainty about whether the Raspberry Pi is actually "credit-card" size (85.60 mm by 53.98 mm according to ISO 7810) or just approximately "credit-card" size (85 mm by 56 mm). Since the Raspberry Pi designers have yet to release an official mechanical drawing, I've decided to wait until my Raspberry Pi order arrives before I start any serious design [1]. As a general comment, I believe that the beta Raspberry Pi boards are rather poorly designed from a packaging/mechanical viewpoint. The new Dangerous Prototypes board templates are much better in that regard.

(link) ~ unknown accuracy...
(link) ~ more examples...

raspberry_pi_diagram.jpg
Raspberry Pi diagram

Picture-001-copy.jpg
Raspberry Pi next to a credit card

Thanks for your time.

dsm

[1] Although my CC case designs just happen to be exactly credit-card size for some unknown reason...

[2] By the way, the Raspberry Pi GPIO connector is now documented and a GPIO expansion board
has been designed. Search for Gertboard (link) for more information.
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