Author Topic: The Living PCB Design Thread  (Read 220579 times)

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Offline mrflow3r

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Re: The Living PCB Design Thread
« Reply #100 on: Thu, 01 January 2015, 15:49:28 »
adafruit is now selling 3 packs of eagle licenses for extremely reasonable prices. anyone interested in splitting a package? kicad is so horrid XD

I'd be down. Which package were you looking at? The 3 seat standard ($1230 USD)?
 

Offline Parak

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Re: The Living PCB Design Thread
« Reply #101 on: Thu, 01 January 2015, 16:42:09 »
Kicad, especially given the recent changes in the past year, has been extremely good to me. Eagle on the other hand was unbearable. Unless one is designing complex fpga 10+ layer boards with RF considerations or somesuch, in which case maybe Altium is more suitable.

Diptrace was also quite nice, but I kept going back to Kicad.. if only Kicad could properly do 3d import and export in step or similar...

Offline SeeThruHead

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Re: The Living PCB Design Thread
« Reply #102 on: Sun, 11 January 2015, 23:05:20 »
realised it was a dumb question
« Last Edit: Sun, 11 January 2015, 23:20:30 by SeeThruHead »
    

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Offline Wilba

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Re: The Living PCB Design Thread
« Reply #103 on: Sun, 15 February 2015, 21:12:04 »
I've seen a couple of keyboard PCBs that cover the through-hole pads on the top side with solder mask. e.g.

90886-0

Does anyone know why this is done? I'm guessing it might make it a tiny bit easier to desolder a switch or LED, since there won't be a pad under the switch for solder to form.
I'm thinking of doing that on the Planck/Atomic PCB but I also prefer to know why something is done a certain way, rather than just copy blindly...



Offline qwack

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Re: The Living PCB Design Thread
« Reply #104 on: Mon, 16 February 2015, 07:28:56 »
I know that it is called tenting when done on vias, but I have no idea how functionally useful it might be for regular pads. Maybe just an aesthetic choice? Or a way to indicate to the user "hey, you have to solder on the other side!"  ;D

In any case, if your pads/drills are sized properly in the first place, desoldering should not be a problem.
« Last Edit: Mon, 16 February 2015, 08:51:52 by qwack »

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Offline jdcarpe

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Re: The Living PCB Design Thread
« Reply #105 on: Mon, 16 February 2015, 09:31:31 »
I've seen a couple of keyboard PCBs that cover the through-hole pads on the top side with solder mask. e.g.

(Attachment Link)

Does anyone know why this is done? I'm guessing it might make it a tiny bit easier to desolder a switch or LED, since there won't be a pad under the switch for solder to form.
I'm thinking of doing that on the Planck/Atomic PCB but I also prefer to know why something is done a certain way, rather than just copy blindly...




I probably would not do that, if it were me. Leaving the through hole pads on both sides allows the solder to flow through and create a fillet on both sides, making a better connection.
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Offline vvp

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Re: The Living PCB Design Thread
« Reply #106 on: Tue, 17 February 2015, 02:56:13 »
Kicad, especially given the recent changes in the past year, has been extremely good to me. Eagle on the other hand was unbearable. Unless one is designing complex fpga 10+ layer boards with RF considerations or somesuch, in which case maybe Altium is more suitable.

Diptrace was also quite nice, but I kept going back to Kicad.. if only Kicad could properly do 3d import and export in step or similar...
I used a git version of kicad for Katy and (especially considering its price) it is good enough for a simple keyboard ... and it would be great if it could import step files.

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #107 on: Thu, 19 February 2015, 16:03:48 »
I am currently stuck with what to do with KiCad and I am following the tutorial exactly, but I am at the point where I am in cvpcb, and I added the KIPRJMOD footprint folder, and the components won't show up and I am stuck. Any help will be great! TIA!


Offline vvp

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Re: The Living PCB Design Thread
« Reply #108 on: Thu, 19 February 2015, 16:52:35 »
You need a local library of footprints only when you are drawing your own footprints.
You need to draw (or import) your own footprints only when you cannot find some suitable footprints in the standard libraries.
You should be able to find standard footprints at least for the diodes.
Select appropriate library on the left (e.g. Diodes_SMD or Diodes_ThroughHole), leave D1 selected in the middle plane, and select filtering to library and pin count (the last 3 icons in the toolbar). You should see some options in the right pane.

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #109 on: Thu, 19 February 2015, 17:04:54 »
You need a local library of footprints only when you are drawing your own footprints.
You need to draw (or import) your own footprints only when you cannot find some suitable footprints in the standard libraries.
You should be able to find standard footprints at least for the diodes.
Select appropriate library on the left (e.g. Diodes_SMD or Diodes_ThroughHole), leave D1 selected in the middle plane, and select filtering to library and pin count (the last 3 icons in the toolbar). You should see some options in the right pane.
I don't see anything after pressing all of those :-(

Offline vvp

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Re: The Living PCB Design Thread
« Reply #110 on: Thu, 19 February 2015, 18:52:29 »
Try to deactivate all 3 filters (keyword, library, and pin count).
Still not seeing anything?

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #111 on: Thu, 19 February 2015, 18:54:52 »
Try to deactivate all 3 filters (keyword, library, and pin count).
Still not seeing anything?
Nope

Offline vvp

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Re: The Living PCB Design Thread
« Reply #112 on: Thu, 19 February 2015, 19:04:45 »
That sucks.
Well, I use it on linux and two more things needed to be done to have kicad footprints working were:
  • setting environment variable KISYSMOD to the directory with footprints (in my case /usr/share/kicad/footprints)
  • copying /usr/share/kicad/footprints/fp-lib-table to ~/.config/kicad
Maybe something similar needs to be done on windows too. Of course, it should have been done by setup. If somebody who uses kicad on windows does not chime in with some ideas then you may try to ask on #kicad IRC channel, or some kicad mailing list. This works fine for me on linux.

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #113 on: Thu, 19 February 2015, 19:32:55 »
That sucks.
Well, I use it on linux and two more things needed to be done to have kicad footprints working were:
  • setting environment variable KISYSMOD to the directory with footprints (in my case /usr/share/kicad/footprints)
  • copying /usr/share/kicad/footprints/fp-lib-table to ~/.config/kicad
Maybe something similar needs to be done on windows too. Of course, it should have been done by setup. If somebody who uses kicad on windows does not chime in with some ideas then you may try to ask on #kicad IRC channel, or some kicad mailing list. This works fine for me on linux.
Thanks!

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #114 on: Thu, 19 February 2015, 21:24:06 »
Apparently the reasons why it won't work is because I need to update the .mod files to the new format?

Offline vvp

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Re: The Living PCB Design Thread
« Reply #115 on: Fri, 20 February 2015, 07:21:11 »
Well, the format of footprint files changed when I changed from about a year old release to a git version.
But the install should copy the new footprint libraries to your PC. And the uninstall of the old version should have removed the old libraries.
On linux, I did not need to upgrade any libraries. I needed to set path to new libraries, update fp-lib-table, and (for the PCB which I needed to modify) I needed to assign footprints from the new libraries. I do not have any experience with windows version of kicad so I do not know how the upgrade would go there.
There is also some way how to pull footprints directly from git (internet) instead of from your local install of kicad. But I do not use it so I'm not sure how that must be setup.

Offline twiddle

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Re: The Living PCB Design Thread
« Reply #116 on: Fri, 20 February 2015, 07:42:04 »
Just curious to see what people think of this, my first attempt at designing a simple prototype dev board for some custom controller work I am doing (this particular design is evaluating a LPC11U35). Once I verify I've got all the hardware I need for a functional chip I intend to look at > 2 layers so I can break out as many of the IOs as possible, etc, but this prototype is going to be etched at home (I manually broke a few IO pins out to a header on the actual board layout you can see here).



Offline sethk_

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Re: The Living PCB Design Thread
« Reply #117 on: Fri, 20 February 2015, 09:42:04 »
Well, the format of footprint files changed when I changed from about a year old release to a git version.
But the install should copy the new footprint libraries to your PC. And the uninstall of the old version should have removed the old libraries.
On linux, I did not need to upgrade any libraries. I needed to set path to new libraries, update fp-lib-table, and (for the PCB which I needed to modify) I needed to assign footprints from the new libraries. I do not have any experience with windows version of kicad so I do not know how the upgrade would go there.
There is also some way how to pull footprints directly from git (internet) instead of from your local install of kicad. But I do not use it so I'm not sure how that must be setup.
I just got around this by  installing an older version of KiCAD, the lazy way.

Offline vvp

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Re: The Living PCB Design Thread
« Reply #118 on: Fri, 20 February 2015, 12:16:15 »
Just curious to see what people think of this...
I did not study your schematic but your PCBs looks very empty.
I etch at home and my experience is that it is easy to do if you have min track width 0.3 mm, min gap 0.25 mm, min via diameter 1 mm, min via drill 0.5 mm. One sided PCBs with these limits are easy to do even using the most simple toner transfer method (and you can put there as many tracks as they fit). If I would need to etch both sides I would probably prefer photo resist since it is easier to align. I typically design them as two sided and I put as much tracks as possible on the back side. I put only straight tracks on the front side so that I can decide not to etch front side but just put Φ0.25 mm wire bridges instead. If there is not too many of front side tracks then I etch only the back side.
You can look how it looks like here: https://geekhack.org/index.php?topic=48851.msg1644678#msg1644678

Edit: And add fill zones if you etch at home. You will save your FeCl3 or whatever you use. You can just create one zone over the whole PCB and assign it to NoNet. So it is easy to add.
« Last Edit: Fri, 20 February 2015, 12:24:39 by vvp »

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #119 on: Fri, 20 February 2015, 12:18:18 »
Does anyone have suggestions on spacing the pads and what not?

Offline twiddle

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Re: The Living PCB Design Thread
« Reply #120 on: Fri, 20 February 2015, 14:57:33 »
min track width 0.3 mm, min gap 0.25 mm

Edit: And add fill zones if you etch at home. You will save your FeCl3 or whatever you use. You can just create one zone over the whole PCB and assign it to NoNet. So it is easy to add.
These were the settings that I used, however trying to do it on a single sided board is next to impossible in situations like this, at least to my understanding:

Unless I use a through-hole cap, it's hard to see how I can route the crystal unless I do something like this:



And that means the decoupling cap is too far from the microcontroller, I think.

good tip about the fill zones, that is easy enough to do.

Offline vvp

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Re: The Living PCB Design Thread
« Reply #121 on: Fri, 20 February 2015, 18:49:09 »
Yes, you probably need a via for the crystal. I do not know whether it is acceptable to put the decoupling capacitor so far away to allow routing around the crystal.

Do you need the crystal? Are internal clock sources that bad? In my case, it is optional. Using an internal clock source is recommended for USB anyway (not sure if it is even possible to use an external clock source for it). And I do not need that precise time for anything else.

Offline twiddle

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Re: The Living PCB Design Thread
« Reply #122 on: Fri, 20 February 2015, 19:26:43 »
Yes, you probably need a via for the crystal. I do not know whether it is acceptable to put the decoupling capacitor so far away to allow routing around the crystal.

Do you need the crystal? Are internal clock sources that bad? In my case, it is optional. Using an internal clock source is recommended for USB anyway (not sure if it is even possible to use an external clock source for it). And I do not need that precise time for anything else.

Almost every chip I am evaluating *requires* the crystal for USB, from Freescale's K22 range through the LPC and STM32s. I guess I could try without and just see, heh. All of their datasheets claim the internal oscillator isn't accurate enough, though.
Went back to it and took another shot at doing everything manually, but with liberal use of vias and the second layer:

Offline vvp

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Re: The Living PCB Design Thread
« Reply #123 on: Sat, 21 February 2015, 05:58:29 »
Interesting. I thought only some old chips (like ATmega) need external crystal for USB. You are using ARM which I thought to be much higher level.

ATxmega does not need external crystal for USB but it may use it if one prefers so (though I do not know why anybody would do it if the internal one is good enough). I would quite like ATxmega also for other things besides keyboards if its ADC would be better.

Offline nandop

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Re: The Living PCB Design Thread
« Reply #124 on: Mon, 23 February 2015, 14:39:34 »
Are there any footprints for the AT90USB1287? I can't seem to find one.
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Offline sypl

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Re: The Living PCB Design Thread
« Reply #125 on: Mon, 23 February 2015, 19:25:00 »
Hi all. Does anyone know how to import the geekhack footprints [https://github.com/geekhack-org/kicad-library/tree/master/modules]? In Cvpcb I do the following:
- Go to 'Edit library table'
- Click on 'project specific libraries'  tab, then click 'append library'
- fill in details with nickname 'geekhack', path as local path (/Users/sypl/keyboards/kicad/libraries/kicad-library/modules), plugin type 'KiCad'
- Click ok,

But when I click on the geekhack library it shows nothing. Only library filter is on.

Offline sethk_

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Re: The Living PCB Design Thread
« Reply #126 on: Mon, 23 February 2015, 19:40:57 »
Hi all. Does anyone know how to import the geekhack footprints [https://github.com/geekhack-org/kicad-library/tree/master/modules]? In Cvpcb I do the following:
- Go to 'Edit library table'
- Click on 'project specific libraries'  tab, then click 'append library'
- fill in details with nickname 'geekhack', path as local path (/Users/sypl/keyboards/kicad/libraries/kicad-library/modules), plugin type 'KiCad'
- Click ok,

But when I click on the geekhack library it shows nothing. Only library filter is on.
Yeah, I had the same issue. What version are you using? If you are using the newest version, download the one from like 7-7-2013, and then add them in using the guide.

Offline sypl

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Re: The Living PCB Design Thread
« Reply #127 on: Mon, 23 February 2015, 19:55:48 »
I didn't manage to import that library, and I think it may be a format thing. There's a new format for modules in kicad it seems. I imported this using the github option and it worked a charm: https://github.com/stormbard/Keyboard.pretty

Offline hasu

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Re: The Living PCB Design Thread
« Reply #128 on: Mon, 23 February 2015, 22:16:31 »
Are there any footprints for the AT90USB1287? I can't seem to find one.

You can find it under library Housings_DFN_QFN or Housing_QFP. But before using you better check it thoroughly with refering datasheet.

https://github.com/KiCad/Housings_DFN_QFN.pretty
https://github.com/KiCad/Housings_QFP.pretty
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Offline hasu

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Re: The Living PCB Design Thread
« Reply #129 on: Mon, 23 February 2015, 22:35:46 »
I can add those footprints with your method but I use path like '/home/noname/tmp/gh-test/tqfp.mod'.

Nickname: tqfp
Library Path: /home/noname/tmp/gh-test/tqfp.mod
Plugin Type: Legacy

Version info of my KiCad.
Code: [Select]
Application: kicad
Version: 0.201501310101+5397~21~ubuntu14.10.1-product Release build
wxWidgets: Version 3.0.1 (debug,wchar_t,compiler with C++ ABI 1002,GCC 4.9.1,wx containers,compatible with 2.8)
Platform: Linux 3.16.0-30-generic x86_64, 64 bit, Little endian, wxGTK
Boost version: 1.54.0
         USE_WX_GRAPHICS_CONTEXT=OFF
         USE_WX_OVERLAY=OFF
         KICAD_SCRIPTING=ON
         KICAD_SCRIPTING_MODULES=ON
         KICAD_SCRIPTING_WXPYTHON=ON
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=ON
         KICAD_USE_WEBKIT=ON


Hi all. Does anyone know how to import the geekhack footprints [https://github.com/geekhack-org/kicad-library/tree/master/modules]? In Cvpcb I do the following:
- Go to 'Edit library table'
- Click on 'project specific libraries'  tab, then click 'append library'
- fill in details with nickname 'geekhack', path as local path (/Users/sypl/keyboards/kicad/libraries/kicad-library/modules), plugin type 'KiCad'
- Click ok,

But when I click on the geekhack library it shows nothing. Only library filter is on.
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Offline sypl

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Re: The Living PCB Design Thread
« Reply #130 on: Tue, 24 February 2015, 05:49:55 »
Ah, legacy, of course. Thanks for that! I like the other library better though, so will stick with that.

I can add those footprints with your method but I use path like '/home/noname/tmp/gh-test/tqfp.mod'.

Nickname: tqfp
Library Path: /home/noname/tmp/gh-test/tqfp.mod
Plugin Type: Legacy

Version info of my KiCad.
Code: [Select]
Application: kicad
Version: 0.201501310101+5397~21~ubuntu14.10.1-product Release build
wxWidgets: Version 3.0.1 (debug,wchar_t,compiler with C++ ABI 1002,GCC 4.9.1,wx containers,compatible with 2.8)
Platform: Linux 3.16.0-30-generic x86_64, 64 bit, Little endian, wxGTK
Boost version: 1.54.0
         USE_WX_GRAPHICS_CONTEXT=OFF
         USE_WX_OVERLAY=OFF
         KICAD_SCRIPTING=ON
         KICAD_SCRIPTING_MODULES=ON
         KICAD_SCRIPTING_WXPYTHON=ON
         USE_FP_LIB_TABLE=HARD_CODED_ON
         BUILD_GITHUB_PLUGIN=ON
         KICAD_USE_WEBKIT=ON


Hi all. Does anyone know how to import the geekhack footprints [https://github.com/geekhack-org/kicad-library/tree/master/modules]? In Cvpcb I do the following:
- Go to 'Edit library table'
- Click on 'project specific libraries'  tab, then click 'append library'
- fill in details with nickname 'geekhack', path as local path (/Users/sypl/keyboards/kicad/libraries/kicad-library/modules), plugin type 'KiCad'
- Click ok,

But when I click on the geekhack library it shows nothing. Only library filter is on.

Offline sypl

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Re: The Living PCB Design Thread
« Reply #131 on: Tue, 24 February 2015, 06:59:39 »
Oops, maybe spoke too soon. The numbers on the pins on the teensy from that library don't match my schematic. Is there a teensy footprint for kicad out there that will match this schematic?

91796-0
91798-1

Offline sypl

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Re: The Living PCB Design Thread
« Reply #132 on: Tue, 24 February 2015, 07:58:06 »
I think I'll just copy the footprint to a new library and re-assign the pin numbers, like so:

91802-0

But I'm not sure what pin numbers to assign to the GND and VCC pins. Can I just pick any of the existing GND pin numbers (35, 43, 23, 15)?

Offline loarto

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Re: The Living PCB Design Thread
« Reply #133 on: Tue, 24 February 2015, 13:26:11 »
I can't manage to import the mx1a.mod to kicad. I'm using (2013-may-18)-stable and I get this message when I try to use it: IO_ERROR: File '/home/plitter/Downloads/mx1a.mod' is empty or is not a legacy library
from /build/kicad/src/stable_2013-05-18_BZR4017/pcbnew/legacy_plugin.cpp : ReadAndVerifyHeader() : line 3984

Any ideas?

Offline sypl

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Re: The Living PCB Design Thread
« Reply #134 on: Tue, 24 February 2015, 18:12:13 »
Did importing tqfp.mod work for you?

Offline loarto

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Re: The Living PCB Design Thread
« Reply #135 on: Wed, 25 February 2015, 08:00:44 »
Hmm, all my own fault. I tried to "Save link as" and didn't check after, so what I got in my mx1a file was just html code :p I copy pasted the file and afterwards I could import it :)

[EDIT:] Anyone have a footprint of a teensy 31? :)
« Last Edit: Wed, 25 February 2015, 15:43:34 by loarto »

Offline sypl

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Re: The Living PCB Design Thread
« Reply #136 on: Fri, 27 February 2015, 13:20:06 »
This is my first attempt at a pcb with kicad.

92206-0

I think it's okay, but when I export to gerber and view it in kicad's gerber viewer it looks kind of strange, with numbers along the lines, like so:

92208-1

Close-up:

92210-2

Is this a bug? Has anyone experienced this before? I tried uploading to OSH Park after renaming the files and it renders ok, so I think the file's are good, but it's just weird seeing them rendered like this.

Offline bpiphany

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Re: The Living PCB Design Thread
« Reply #137 on: Fri, 27 February 2015, 14:11:00 »
Those numbers are just the "aperture" used for that item in the gerber files. They will be quite useful if you want to muck around in the gerbers yourself. The gerber files are really simple. The file format description is short and a nice read if you are interested in hacking something fun onto your circuit boards. The %LPC*% and %LPD*% commands or G36/G37 for polygons, and so on.

Offline MOZ

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Re: The Living PCB Design Thread
« Reply #138 on: Fri, 27 February 2015, 14:11:36 »
You have to select which elements you want to view in KiCAD.

Offline qwack

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Re: The Living PCB Design Thread
« Reply #139 on: Thu, 19 March 2015, 15:52:40 »
Does anyone have recommendations regarding trace width and spacing (/isolation) ? More specifically, I'd like to know if 16 mil is a safe value for the traces connecting switches, and if it is okay with LEDs as well. I know there are calculators which outputs recommended values depending on the current carried by the traces, but I'm more interested in practical experience. What do you guys generally use for your keyboard PCBs?

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Offline sypl

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Re: The Living PCB Design Thread
« Reply #140 on: Thu, 19 March 2015, 20:12:34 »
What would happen if I were to connect two or more mini (or micro) usb ports for data transfer to the same pins? I was thinking it would be nice to have a keyboard with ports top, left and right. Top would be useful if using desktop and long cable; left and right would be useful for short cables on top of laptops. If someone went crazy and plugged in all three would it fry the board or something? Would it read as three keyboards?

Offline sypl

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Re: The Living PCB Design Thread
« Reply #141 on: Thu, 09 April 2015, 13:49:56 »
Makes me a little sad to see I was the last poster in this thread almost a month ago... No PCB love?

Anyway, I had another question. I want to make a PCB with the atmega32u4, but waaaaaay stripped down from the teensy2.0. I only need 16pins and a usb connector, and that's it (I think).

Given this schematic [https://www.pjrc.com/teensy/schematic2.gif], how much of this can I junk? For the usb I have to connect d+, d-, uvcc, ugnd and vbus it looks like, as well as some capacitors. And I think it's safe to get rid of the reset button, right? I can reset via software, yes? Would that do it?

Offline bpiphany

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Re: The Living PCB Design Thread
« Reply #142 on: Thu, 09 April 2015, 14:33:03 »
What would happen if I were to connect two or more mini (or micro) usb ports for data transfer to the same pins? I was thinking it would be nice to have a keyboard with ports top, left and right. Top would be useful if using desktop and long cable; left and right would be useful for short cables on top of laptops. If someone went crazy and plugged in all three would it fry the board or something? Would it read as three keyboards?

This will probably work. You aren't exactly expecting USB3 speed or anything.. Don't plug more than one in. I don't know for sure what will happen to the data lines, if they could short out or something.


Makes me a little sad to see I was the last poster in this thread almost a month ago... No PCB love?

Anyway, I had another question. I want to make a PCB with the atmega32u4, but waaaaaay stripped down from the teensy2.0. I only need 16pins and a usb connector, and that's it (I think).

Given this schematic [https://www.pjrc.com/teensy/schematic2.gif], how much of this can I junk? For the usb I have to connect d+, d-, uvcc, ugnd and vbus it looks like, as well as some capacitors. And I think it's safe to get rid of the reset button, right? I can reset via software, yes? Would that do it?


Until you eff up the software... At least route Reset out to a pad on the board. That makes it a bit easier to jumper it to ground than trying to hit the correct pin on the chip. You don't need an actual button.

You should really keep most of the components. Drop the LED and resistor, reset button, and perhaps use the same capacitor for bypassing VCC and AVCC. You also of course don't need the footprints for the voltage regulator and such.

Offline sypl

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Re: The Living PCB Design Thread
« Reply #143 on: Sat, 11 April 2015, 19:13:30 »
Hey, thanks for the reply bpiphany. Another question. In the schematic what are the rectangular pads, where it says 5V and 3V next to them? Are these pads for fuses? Do I need both of them?

This is what I have so far:
97034-0


Offline bpiphany

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Re: The Living PCB Design Thread
« Reply #144 on: Sun, 12 April 2015, 02:58:00 »
The rectangular pads are for a voltage regulator. It makes it possible to run the ATmega at 3.3V instead of 5V which could possibly be handy if you have other peripherals made for 3.3V. You can forget all about that.

Your capacitors in the top left corner are not connected correctly. You ideally want at least a 10F capacitor between VCC and GND anywhere in your design, an electrolyte will be good. Then you want 0.1F or 1.0F "bypass" capacitors at every VCC pin to ensure you don't ever so momentarily drop the supply voltage at that pin, and also to filter out some EMI (I think). The datasheet should hold more info on which value capacitors to use where. Here you want small ceramic capacitors to be able to place them close to their supply pin.

Offline vvp

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Re: The Living PCB Design Thread
« Reply #145 on: Sun, 12 April 2015, 09:14:07 »
ESD protection is missing which I think is OK.
Additional LC filter for AVcc is missing which is OK if you do not care that much about ADC.
External Crystal is missing which I think is bad if you want to use USB.

Offline vvp

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Re: The Living PCB Design Thread
« Reply #146 on: Sun, 12 April 2015, 09:26:17 »
Here is a schematic I found somewhere which has:
  • ESD protection,
  • an additional power filter for AVcc,
  • external crystal.
Compared to your version there is also external ARef and PE2 is not dedicated as HWB.

Offline sypl

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Re: The Living PCB Design Thread
« Reply #147 on: Wed, 22 April 2015, 13:17:52 »
Your capacitors in the top left corner are not connected correctly. You ideally want at least a 10F capacitor between VCC and GND anywhere in your design, an electrolyte will be good. Then you want 0.1F or 1.0F "bypass" capacitors at every VCC pin to ensure you don't ever so momentarily drop the supply voltage at that pin, and also to filter out some EMI (I think). The datasheet should hold more info on which value capacitors to use where. Here you want small ceramic capacitors to be able to place them close to their supply pin.

Thanks for the replies, bpiphany and vvp. You say I need a bypass capacitor at each VCC, but if I don't intend to use any of them other than the one connected to the usb, is this still necessary? Can I just leave them unconnected?

Offline bpiphany

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Re: The Living PCB Design Thread
« Reply #148 on: Wed, 22 April 2015, 14:14:55 »
They are not for you to use - they are for you to supply with power.
« Last Edit: Wed, 22 April 2015, 14:17:21 by bpiphany »

Offline sypl

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Re: The Living PCB Design Thread
« Reply #149 on: Wed, 22 April 2015, 14:44:22 »
They are not for you to use - they are for you to supply with power.

Please be patient, I'm pretty new to the pcb game. Pins 14 and 34 are VCC pins on my teensy. I don't use them so am not supplying power to them, so my thinking was that I could skip connecting them. Similarly ground pins 15 and 35. Is this logic faulty?