Bus Pirate SOB case review

Standard PCB templates and project cases

Re: Standard, beautiful PCB cases

Postby dsm » Tue Jan 03, 2012 11:45 am

comment

ian wrote:I like the enclosed case. Is there a way to combine it with mounting holes? Through the acrylic on one side maybe? The nut could be capped with a rubber foot. Just a thought.

I suspect that the external case frame as I described above is probably not cost effective (especially compared to injection molded beige cases). On the other hand, you might want to consider going down the KickStarter (link) route to get the extruded edge segments made if you like this approach.

I've sometimes used swaged standoffs (link) to hold a board-to-a-board or a board-to-a-case. In the back of my mind, I was thinking of swaged standoffs on the BusPirate with machine screws through the bottom laser cut acrylic surface window.

The original slide-in-from-the-side yaobls case I designed had an acrylic window only on the top. I thought about how to make make a BusPirate variant using what I learned from the yaobls case design, but life and other disasters keep getting in the way.

I remember calculators and other products with little rubber plug feet that covered their case screws. I am not sure how to apply that approach in this situation. The feet in the yaobls, yabp, yabc, and yacc case designs only add 0.5 mm to the overall height of the enclosure, cost only a couple cents worth of plastic, and can't get lost.

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby dsm » Tue Jan 03, 2012 12:53 pm

distance from center-of-mounting-hole to edge-of-board

jer wrote:Thanks for your notes. Do you think moving the holes 4mm from the corners would be enough? I'm afraid there wouldn't be enough room for the shrouded IO connector (for the Bus Pirate v4) if the holes are moved beyond 4mm from the corners.

I think the answer depends on the diameter of the mounting hole boss on the top case (which is the most likely to interfere with the IO connector shell). For example, assuming 3.0 mm diameter neodymium magnets, we have
    4.0 mm (center-of-mounting-hole to edge-of-board) +
    1.5 mm (1/2 diameter-of-magnet) +
    1.5 mm (mounting boss wall thickness)
    = 7.0 mm

    Twice (each side) this is 14.0 mm.
    37.0 mm (width of the board) -
    14.0 mm
    = 23.0 mm
Using a 4.0 mm center-of-mounting-hole to edge-of-board distance with a shrouded 10-pin male header like BusPirate v3.5e is no problem. Since length of the 12-pin shrouded male header Seeed Studio is using for BusPirate v4c is 22.9 mm, a 4.0 mm center-of-mounting-hole to edge-of-board distance initially looks marginal.

The neodymium magnet diameter is a worst case, however, and I can safely reduce the top case mounting boss wall thickness to 1.0 mm which adds twice 0.5 mm or 1.0 mm of margin. Note that I can still use a wider mounting hole boss on the bottom case to accommodate the head of a 2.9 mm x 8.0 mm screw.

So using a 3.5 mm center-of-mounting-hole to edge-of-board distance is a safer choice, but using a 4.0 mm center-of-mounting-hole to edge-of-board distance is a more useful choice.

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby dsm » Tue Jan 03, 2012 1:13 pm

keep out area

jer wrote:Looking at the clamshell foot screw diagram: Should 3mm and 4.2mm from the center of the holes be defined as component keepout areas for the top and bottom respectively?

The short answer is that you are exactly right (based on the clamshell yabp case foot screw detail drawing).

The more complicated answer is that in order to avoid loose leftover nylon powder from the Shapeways SLS 3D printing process, I've been extending my mounting bosses sideways (see image below) to the inside case wall. I don't think any component locations are affected. This is a design detail that the injection molding folks specifically avoid because a thicker wall is visible on the outside of the case (see the Proto Labs site for more details), but is not a problem with SLS 3D printing.

IMG_0741-edit.jpg
clamshell-yabp-case-bottom-dsm-v3 (interior)

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby dsm » Tue Jan 03, 2012 1:34 pm

which program

tayken wrote:standard pin headers are around 12 cm high

Hmmm... I measure 8.5 mm for the female headers on the OBLS board and 8.9 mm for height of the 12-pin shrouded male header Seeed Studio is using for BusPirate v4c board.



Although I have Dassault Systèmes SolidWorks (to create parts for PCB layout simulation), I used Autodesk Inventor Professional 2012 for the BusPirate-case-frame 60.2 x 37.2 x 8.5 (assembled) image. Our local TechShop (link) has a deal with Autodesk to provide members with a free copy of Inventor Professional 2012 and free training (unfortunately for a limited time). I've also used Google SketchUp and PTC Creo 4.0 for various projects.

One of the nice things about Autodesk Inventor Professional 2012 is that there is a design mode for injection molded plastic cases (e.g. adjustable draft angle during extrusion cuts, snap finger and indentation wizard, etc.).



For some reason, 1.5 mm thick acrylic is much easier for me to find locally than 1.0 mm acrylic.

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby dsm » Tue Jan 03, 2012 2:03 pm

more case alternatives

You've probably seen transparent product boxes made out of thin folded and ultrasonically welded plastic (link) (link).
Such cases are only $0.60 or so in moderate quantities.
They are probably strong enough to tolerate light handling, but I wouldn't drop them in my toolbox.

My local plastics supplier Tap Plastics (link) offers a variety of small plastic boxes.
    Plastic boxes with transparent tops and colored bottoms (link).
    Plastic boxes with friction fit covers in various transparent colors (link) (link).
    Flex-hinge polypropylene plastic boxes (link)
How about a vacuum-formed clamshell case complete with ribs to increase stiffness?
A wooden or clay form is easy to make.

Ask the Adafruit Industries folks who makes their clear and white enclosures for the Arduino.
Try to get the same company to make your cases.
You may be able to share the upfront costs with Adafruit Industries since they carry the Bus Pirate.

Ask the Arduino folks who makes their A000009 Arduino Enclosure.
Try to get the same company to make your cases.

Have you spoken with the Shenzhen Hongfashunda Mold Co., Ltd. (link) folks?
The tops of their plastic waterproof boxes look like the right material.

How about using just the top from the Seeed Studio Seeeduino Stalker v2 enclosure (link)?
Throw away the beige bottom case and design a new flat bottom plate.

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby ian » Wed Jan 04, 2012 3:53 am

A massive amount of great info, thank you.

It sounds like we need to carefully consider the hole placement and screw head size to avoid interfering with the shroud. Jer, do you have any concerns or have you figured it all out?
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Re: Standard, beautiful PCB cases

Postby fcobcn » Wed Jan 04, 2012 6:25 am

Found a good place to help us escape from beige:
https://www.inventables.com/categories/ ... lic-sheets

I suggest to use this:
https://www.inventables.com/technologie ... ylic-sheet

This online store has amazing products, have a look at them
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Re: Standard, beautiful PCB cases

Postby dsm » Wed Jan 04, 2012 6:45 am

USB connector position

jer,
ian,

I've been an advocate for placing any components that interact with the enclosure on a coarser grid - say 0.5 mm or even 1.0 mm. In the latest round of discussion about the Bus Pirate v3.5e and v4c layouts, the proposed position for the USB connector was moved to (5.5, 18.5). While reviewing the data sheet for the Kobiconn 154-15320-E Type B 5-pin mini-USB connector used on many Dangerous Prototypes designs, I noticed that the recommended origin for this connector is 5.25 mm from the edge of the board. This placement allows the connector to hang over the edge of the board slightly in order to maximize engagement margins with the mating mini-USB plug. The placement of this connector also affects the maximum wall thickness for the enclosure given the USB specification for the minimum spacing between the receptacle face and the mini-USB plug overmold boot [1].

I now recommend that the mini-USB receptacle be moved to (5.25, 18.5).

KC-301260.pdf
Kobiconn 154-15320-E data sheet
(93.99 KiB) Downloaded 219 times

Thanks for your time.

dsm

[1] Although you can always cut a large enough hole in the case for the entire mini-USB plug overmold boot.
This is commonly done for stacked laser cut acrylic cases since the enclosure walls are so thick.
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Re: Standard, beautiful PCB cases

Postby Jer » Wed Jan 04, 2012 8:33 am

Hi,

I just uploaded the new v3.5e and v4c to the SVN (revision 1627)


Updates:
moved holes' center 4mm from the corner,
holes are not plated,
moved push buttons of v4c, now with symmetry
moved ICSP connectors of v3.5e and v4c
Y-axis position of push buttons and ICSP connectors are the same (v4c)
moved USB connectors of v3.5e and v4c according to the suggestion of DSM
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Re: Standard, beautiful PCB cases

Postby ian » Wed Jan 04, 2012 11:29 am

Thanks Jer, DSM.

fcobcn - the acrylic looks great. Are you a fan of red/purple/pink? I noticed the acrylic was florescent pink, and the case prototypes are also red/purple/pink depending on the light :) I like it, it really pops and the edges glow.
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Re: Standard, beautiful PCB cases

Postby fcobcn » Wed Jan 04, 2012 4:16 pm

ian wrote:Are you a fan of red/purple/pink?


Yep, I'm a believer that hacking tools should be pink : )
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Re: Standard, beautiful PCB cases

Postby dsm » Wed Jan 04, 2012 5:00 pm

BusPirate-v3.5e-SSOP.brd [r1627] comments
BusPirate-v4c.brd [r1627] comments

I looked at the BusPirate-v3.5e-SSOP.brd [r1627] board layout and have a couple comments.
I looked at the BusPirate-v4c.brd [r1627] board layout and have a couple comments.

  • The overall dimensions for both boards is 60.0 mm x 37.0 mm.
    These dimensions are approximately golden ratio to the nearest 1.0 mm.
    This allows the the major and minor board center-lines to be on a 0.5 mm grid. Nice.
  • The 3.2 mm mounting holes for both boards are symmetrically positioned 4.0 mm inward from the corners. Nice.
  • The center of the USB connector is at the same position (5.25, 18.5) for both boards.
    Positioned on the major axis board center-line. Nice.
  • The center of the ICSP connector is at the same position (30.0, 3.5) for both boards.
    Positioned on the minor axis board center-line. Nice.
  • The center of the IO connector is at the same position (51.5, 18.5) for both boards.
    Positioned on the major axis board center-line. Nice.
  • The center of the ExtPwr connector (v4c only) on a 1.0 mm grid. Nice.
  • The center of the push-buttons (v4c only) are on a 0.5 mm grid.
    The push-buttons are positioned symmetrically around the minor axis board center-line. Nice.
  • The center of the LEDs are at the same positions for both boards on a 1.0 mm grid.
    The LEDs are positioned symmetrically around the minor axis board center-line. Nice.
The only other comment I have is a fairly minor aesthetic issue. You might want to revisit your corner radius choice now that the mounting holes have been symmetrically positioned 4.0 mm inward from the corners. A corner radius of 4.0 mm would allow a constant distance between the edge-of-the-mounting-hole and the edge-of-the-board. You might also want to document your corner radius choice on layer 47 (Measures).

Bus-Pirate-v3.5e-board-geometry-v016-xlsx.pdf
Bus-Pirate-v3.5e-board-geometry-v016 [r1627]
(57.03 KiB) Downloaded 231 times

Bus-Pirate-v4c-board-geometry-v016-xlsx.pdf
Bus-Pirate-v4c-board-geometry-v016 [r1627]
(57.46 KiB) Downloaded 251 times

My $0.02 worth.

Thanks for your time.

dsm
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Re: Standard, beautiful PCB cases

Postby ian » Thu Jan 05, 2012 4:03 am

Thank you again for your thoughtful analysis.

A corner radius of 4.0 mm would allow a constant distance between the edge-of-the-mounting-hole and the edge-of-the-board. You might also want to document your corner radius choice on layer 47 (Measures).


Sounds good to me.
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Re: Standard, beautiful PCB cases

Postby Jer » Fri Jan 06, 2012 8:01 am

Corner radius of BP boards has been changed to 4mm (SVN revision: 1654 )
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Re: Standard, beautiful PCB cases

Postby dsm » Fri Jan 06, 2012 3:45 pm

BusPirate-v3.5e-SSOP.brd [r1654] comments
BusPirate-v4c.brd [r1654] comments

I looked at the BusPirate-v3.5e-SSOP.brd [r1654] board layout and have a couple comments.
I looked at the BusPirate-v4c.brd [r1654] board layout and have a couple comments.

  • No change in [1627] positive comments. Nice.
  • The corner radius now 4.0 mm for both boards. Nice.
Bus-Pirate-v3.5e-board-geometry-r1654-xlsx.pdf
Bus-Pirate-v3.5e-board-geometry-v016 [r1654]
(58.25 KiB) Downloaded 218 times

Bus-Pirate-v4c-board-geometry-r1654-xlsx.pdf
Bus-Pirate-v4c-board-geometry-v016 [r1654]
(58.33 KiB) Downloaded 232 times

Thanks for your time.

dsm
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