ceteras
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Basic IO board for the CM

Wed Apr 09, 2014 12:29 pm

Designing an IO board for the CM is a lot of work, but that doesn't mean one should not try it, for an exercise at least.
I've created a small eagle 6.5 schematic containing only a DDR2 sodimm socket, where each pin has its name according to the Computing Module pinout.
So it is a starting point for anybody who wants to make a schematic.
All you have to do is add your own parts then add wire labels with the same name as those on the CM, and Eagle will make the connections. I believe this is the cleanest way to do it (rather than making a spaghetti of wires).
The .sch and .brd files can be found on github here: https://github.com/ceteras/basicComputeBoard
It's my first time using github, I hope I didn't screw it up.
Of course I would really appreciate anybody's contributions to this.

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killor
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Re: Basic IO board for the CM

Wed Apr 09, 2014 4:27 pm

Hi !
I just installed the freeware version EAGLE 6.5
I tried to open your archive and Eagle shows me :
Error:
line 7 column 18: This is not an EAGLE file.
:(

Am I missing something? THK!!
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ceteras
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Re: Basic IO board for the CM

Wed Apr 09, 2014 4:55 pm

You need to extract the archive, you will get a folder with the two files in it: basicBoard.brd and basicBoard.sch .
Open those with eagle.

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killor
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Re: Basic IO board for the CM

Wed Apr 09, 2014 7:15 pm

Solved thanks! :D
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Re: Basic IO board for the CM

Wed Apr 09, 2014 10:35 pm

Well that's a nice start, thanks!
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elektrknight
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Re: Basic IO board for the CM

Thu Apr 10, 2014 3:36 am

@ceteras
ceteras wrote: I've created a small eagle 6.5 schematic containing only a DDR2 sodimm socket, where each pin has its name according to the Computing Module pinout.
So it is a starting point for anybody who wants to make a schematic.
Excellent resource, starred it!
ceteras wrote: It's my first time using github, I hope I didn't screw it up.
Of course I would really appreciate anybody's contributions to this.
Worked fine with Eagle 6.5 but I did not have time to look into it.
I will have more time over the weekend to check etc.
Also, we need to get it converted to KiCad.
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jbeale
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Re: Basic IO board for the CM

Thu Apr 10, 2014 5:11 am

If it helps, there is a script which converts Eagle schematics into KiCad: Eagle2Kicad conversion script http://www.circuitbee.com/help/eagleimport

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elektrknight
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Re: Basic IO board for the CM

Thu Apr 10, 2014 1:10 pm

jbeale wrote:If it helps, there is a script which converts Eagle schematics into KiCad: Eagle2Kicad conversion script http://www.circuitbee.com/help/eagleimport
Good find! Tried it but KiCad can not read converted schematic, complains about undefined DRAW command which seems to be a generic problem with these conversion scripts.

Also tried eagle2kicad-1.2.ulp from http://www.modulbot.com/download.html. This time got a bit further, KiCad can read the schematic but there is a problem with scale. DDR2 symbol is HUGE and and I can not even zoom out enough to see it.

So some progress, but need to look for solutions to the conversion problems.
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ceteras
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Re: Basic IO board for the CM

Thu Apr 10, 2014 1:29 pm

I believe at this level the schematic should be easy to be directly created in KiCad, by someone experienced.
It's only a part, after all.

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Re: Basic IO board for the CM

Thu Apr 10, 2014 2:30 pm

elektrknight wrote:
jbeale wrote:If it helps, there is a script which converts Eagle schematics into KiCad: Eagle2Kicad conversion script http://www.circuitbee.com/help/eagleimport
Good find! Tried it but KiCad can not read converted schematic, complains about undefined DRAW command which seems to be a generic problem with these conversion scripts.

Also tried eagle2kicad-1.2.ulp from http://www.modulbot.com/download.html. This time got a bit further, KiCad can read the schematic but there is a problem with scale. DDR2 symbol is HUGE and and I can not even zoom out enough to see it.

So some progress, but need to look for solutions to the conversion problems.
The DDR is huge because memory chips now contain a lot more memory.

Probably.
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Re: Basic IO board for the CM

Thu Apr 10, 2014 4:44 pm

jamesh wrote:
The DDR is huge because memory chips now contain a lot more memory.

Probably.
You mean schematic symbol should be proportional to the size of memory? I like it :-)

Any chance foundation could release module schematic or at least part of it in a format that we could use rather then us trying to re-create it from the PDF?
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Re: Basic IO board for the CM

Thu Apr 10, 2014 6:54 pm

elektrknight wrote:
jamesh wrote:
The DDR is huge because memory chips now contain a lot more memory.

Probably.
You mean schematic symbol should be proportional to the size of memory? I like it :-)

Any chance foundation could release module schematic or at least part of it in a format that we could use rather then us trying to re-create it from the PDF?
I'm sure it's on it way.

(resistor/capacitors/inductors should also be larger in CAD programs depending on their capacity)
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Re: Basic IO board for the CM

Thu Apr 10, 2014 11:24 pm

it would also be usefull if the starting schematic would have the basic power supply on it, so you just tie something to the 5v bus and data pins

ceteras
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Re: Basic IO board for the CM

Fri Apr 11, 2014 7:23 am

cleverca22 wrote:it would also be usefull if the starting schematic would have the basic power supply on it, so you just tie something to the 5v bus and data pins
This is what I want to do next.

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elektrknight
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Re: Basic IO board for the CM

Fri Apr 11, 2014 1:30 pm

ceteras wrote:I believe at this level the schematic should be easy to be directly created in KiCad, by someone experienced.
It's only a part, after all.
Somebody already did :-)

Image

Now somebody has to use the most effective development method of edit,copy and paste to extricate the required components which btw are licensed under GPL 3.

But that means using one's brain to click the mouse around rather then spend next week heroically tilting at windmills in La Mancha I mean fixing obscure conversion scripts, tough choice to make.

http://www.gplsquared.com/SoM2/SoM2.html
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Re: Basic IO board for the CM

Fri Apr 11, 2014 9:19 pm

I wonder what would the limits be for a two-layers board?
A four-layers pcb seems a little too much for me right now.

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Re: Basic IO board for the CM

Sat Apr 12, 2014 1:58 am

ceteras wrote:I wonder what would the limits be for a two-layers board?
A four-layers pcb seems a little too much for me right now.
If you need to use any of the differential signals: HDMI, CAM,DSI and even USB routing on 2 layers will be difficult.
2 layer carrier board with some GPIO (UART, I2C, SPI) should be doable.
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Re: Basic IO board for the CM

Sat Apr 12, 2014 2:25 pm

ceteras wrote:A four-layers pcb seems a little too much for me right now.
It doesn't seem outrageously expensive. You can get three copies of a 4-layer board made for $10 per square inch from https://oshpark.com/pricing That is actually quite a reasonable price for a prototype. A minimal connector setup should not need a lot; the complete Raspberry Pi Model A/B board is less than 8 square inches and you should be able to do better than that. You would not have the main SoC chip on your board, and you could eliminate any connectors you don't use, or use smaller versions.

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Re: Basic IO board for the CM

Sat Apr 12, 2014 5:18 pm

jbeale wrote: It doesn't seem outrageously expensive. You can get three copies of a 4-layer board made for $10 per square inch from https://oshpark.com/pricing That is actually quite a reasonable price for a prototype. A minimal connector setup should not need a lot; the complete Raspberry Pi Model A/B board is less than 8 square inches and you should be able to do better than that. You would not have the main SoC chip on your board, and you could eliminate any connectors you don't use, or use smaller versions.
Many "rapid prototyping" PCB shops will do small/medium volume PCBs on 4 layers quite cheaply as long as you go with their standard design / stackup. They do this so they can aggregate multiple designs on a single production panel.

The board type they offer will be a "one size fits all" but usually this will be sufficient for most needs. You could probably do the high-speed differential interfaces with a 4-layer PCB if you enquire as to their recommended geometries for differential traces.
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Re: Basic IO board for the CM

Sat Apr 12, 2014 6:26 pm

jdb wrote:Many "rapid prototyping" PCB shops will do small/medium volume PCBs on 4 layers quite cheaply as long as you go with their standard design / stackup. They do this so they can aggregate multiple designs on a single production panel.
That's what I've heard, although if you know of any place that beats the OSH Park price for small orders, please do tell.
At work the rapid prototype service we use has a lot charge starting around $500 regardless of size or layers.

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Re: Basic IO board for the CM

Sat Apr 12, 2014 7:30 pm

Seeedstudios prices are insane. 99c each for my 10 MIDI 2-layer PCBs, no other costs. Free shipping. Basically, $9.99 for 10 PCBs. Longish shipping from China (2 weeks) but seriously, insane prices.

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Re: Basic IO board for the CM

Sat Apr 12, 2014 9:25 pm

Would: http://www.rs-online.com/designspark/el ... -libraries
allow me to use the eagle .sch and .brd files that ceteras has produced?
Thanks ceteras.

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Re: Basic IO board for the CM

Tue Apr 15, 2014 12:49 pm

elektrknight wrote:
ceteras wrote:I wonder what would the limits be for a two-layers board?
A four-layers pcb seems a little too much for me right now.
If you need to use any of the differential signals: HDMI, CAM,DSI and even USB routing on 2 layers will be difficult.
2 layer carrier board with some GPIO (UART, I2C, SPI) should be doable.
This means it's not impossible to work with 2 layers.
Eagle has some pretty good support for manually routing differential pairs.

I've once built a single sided pcb having an LVDS transmitter on it, and it worked. And I have a 2 layers pcb made by someone else, with DVI input on an HDMI connector and LVDS transmitter.
I used both of them at 1024x768, so perhaps at those specs it is ok. 1280x800 might also work too, it's not that much different, and I'm not sure I could find a chip for higher resolutions.

@arm2 : I don't know, give it a try, if it fails, do it directly in design spark, it's not that much of a hassle. A lot of GND's, a lot of GPIO's, and the rest is easy. I don't know about the footprint.

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Re: Basic IO board for the CM

Thu Apr 17, 2014 8:44 pm

omenie wrote:Seeedstudios prices are insane. 99c each for my 10 MIDI 2-layer PCBs, no other costs. Free shipping. Basically, $9.99 for 10 PCBs. Longish shipping from China (2 weeks) but seriously, insane prices.
I am a little off topic but here goes. Once the prototyping of a design has been done and a company like Seeedstudios has been completed where is the best place for having the PCB's populated? Small run offs of initially, say 10 off then larger quantities if product is successful.

Also is there a part of the forum where I can find an electronics engineer or an external source similar to Freelancer.com but for electronics design?

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Re: Basic IO board for the CM

Thu Apr 17, 2014 11:18 pm

ilovemipi wrote:
omenie wrote:Seeedstudios prices are insane. 99c each for my 10 MIDI 2-layer PCBs, no other costs. Free shipping. Basically, $9.99 for 10 PCBs. Longish shipping from China (2 weeks) but seriously, insane prices.
I am a little off topic but here goes. Once the prototyping of a design has been done and a company like Seeedstudios has been completed where is the best place for having the PCB's populated? Small run offs of initially, say 10 off then larger quantities if product is successful.

Also is there a part of the forum where I can find an electronics engineer or an external source similar to Freelancer.com but for electronics design?
You can find a lot of people who have done this kind of thing at dangerousprototypes.com, have a look through their forum.
For small qty. like 10 pieces you can probably have a stencil made, and do the solder paste application and toaster-oven reflow trick yourself. Many people have, do a search on YouTube if you aren't familiar with that process.

I have not used them for board stuffing but I believe seeedstudio.com has that capability. They do want you to use only parts on their OPL (open parts library) http://www.seeedstudio.com/wiki/Open_parts_library which includes a microSD card socket, but not a HDMI connector for example.

from : http://www.seeedstudio.com/service/inde ... &type=pcba "Seeed provide 2 pieces-10 pieces PCB assembly service for OPL components. Lead time is 3 days (excluding Chinese Holiday)."

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