Briarios
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Multi Server CM Board

Wed Apr 15, 2015 1:41 pm

Hello again Everyone, :D

Since my last little project was a success in terms of getting the test board to work. I have now come back with some good news :D I have been slaving away on a hot monkey brain to get the new design that I have been working on out the door to show to the good folks of this forum on what I have created and to get some feedback on the design.

For this design as noted by the title is indeed a multi server based board that is designed to hold 4 Compute Modules together with the LAN9512 to have USB and Ethernet per Module. This board is not intended for Cluster work( but can be used that way), It was intended for the general public to have the ability to have 4 separate servers on a single board connected via a single network port and a single power point to power all 4 units at once. It was designed that way so that you do not need to buy extra parts or a network switch to get the same outcome.

With the layout of the board I have made 2 of the 4 Modules have the ability to attach Hats to the board via the 40pin output similar to the Pi Model B+ so that people can control a range of hats or have the ability to do other things with the pins without needing to buy an Extra Pi. (Spacer maybe required for Hats)

And lastly the technical bits you have all been waiting for!, for configuring new CMs I have included HDMI and USB Boot functionality to one of the Modules so that you can configure fresh CMs without the need of any other tools. The whole board will run at 5 Volts but at 10 Amps (due to 4 CMs being on the one board). There is a 5 Port 100Mb Switch on the same board so that all 4 CMs can get network connectivity without the need of an extra switch, which solves the problem alot of people have when they have more than one Pi. Size will be 200x100mm which should be an ideal size.

So there you have it people :lol: I have placed links of the schematics and what the board may look like at the bottom so hopefully you will get a chance to have a look at it. 8-) my next job now is to get the BOM created so i can see on how much the board is going to cost in parts hahaha :lol:

Note: I am not an engineer in any shape or form(this is a side hobby) so please let me know if I have missed anything important in the schematic or board.

Schematic http://pmfg.me/rpi/Multi_Server_MK2/Mul ... .0-sch.pdf
Top http://pmfg.me/rpi/Multi_Server_MK2/Mul ... .0-top.pdf
Bottom http://pmfg.me/rpi/Multi_Server_MK2/Mul ... 0-back.pdf
Image

Comments are always welcome ;)
http://rpi.pmfg.me -- Test board Eagle Cad Files.

mikerr
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Re: Multi Server CM Board

Wed Apr 15, 2015 2:04 pm

I want one already ! :)
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RaTTuS
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Re: Multi Server CM Board

Wed Apr 15, 2015 2:09 pm

awesome!
you can get 5 port nic solutions
i.e. 4x 100mbps with a 1g uplink port [all on one chip]

I forget the model number but have posted before
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Briarios
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Re: Multi Server CM Board

Wed Apr 15, 2015 9:55 pm

RaTTuS wrote:awesome!
you can get 5 port nic solutions
i.e. 4x 100mbps with a 1g uplink port [all on one chip]

I forget the model number but have posted before
I tried to look for that part you had mentioned but I cannot find it, I will continue to search for it however :)


Mikerr it is Great you want one :D If there is enough Interest I will have a look into a Kick starter or something, just getting the interest is the main thing at the moment :lol:
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amk
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Re: Multi Server CM Board

Thu Apr 16, 2015 6:20 am

Why use a two layer board? This sort of circuitry requires good signal integrity for the high speed signals and a low impedance (low for high frequency) power distribution network. Such a board will probably radiate to much and be too susceptible for exteranal noise sources. I would at least use a 4 layer board, you can use the internal planes for low impedance power distribution, shielding/cancelation and return path. Use a thin pre-preg between the internal layer and the top layer so you can easy design the right controlled impedance traces for USB, HDMI and Ethernet. This will greatly benefit signal integrity and give much better EMC behaviour, at only little extra cost.

Briarios
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Re: Multi Server CM Board

Thu Apr 16, 2015 7:19 am

amk wrote:Why use a two layer board? This sort of circuitry requires good signal integrity for the high speed signals and a low impedance (low for high frequency) power distribution network. Such a board will probably radiate to much and be too susceptible for exteranal noise sources. I would at least use a 4 layer board, you can use the internal planes for low impedance power distribution, shielding/cancelation and return path. Use a thin pre-preg between the internal layer and the top layer so you can easy design the right controlled impedance traces for USB, HDMI and Ethernet. This will greatly benefit signal integrity and give much better EMC behaviour, at only little extra cost.
I do actually use a 4 layer board it just doesn't show it in the Pictures because I turned off the middle layers so that it is clearer for everyone to see ;)
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RaTTuS
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Re: Multi Server CM Board

Thu Apr 16, 2015 7:52 am

http://www.davicom.com.tw/userfile/2424 ... 080511.pdf
is one that I found

this is something that I would consider kickstarted ;-p
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Briarios
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Re: Multi Server CM Board

Thu Apr 16, 2015 10:50 am

RaTTuS wrote:http://www.davicom.com.tw/userfile/2424 ... 080511.pdf
is one that I found

this is something that I would consider kickstarted ;-p

Thanks for the link RaTTuS, if you have any schematics on it would be great :) but I will definitely look into that and see if I can get that or something similar. :D

just now need more people to see if they have any interest :lol:
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Briarios
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Re: Multi Server CM Board

Sat Apr 18, 2015 4:03 am

Ok So i have had a look at the Switch IC you have posted RaTTuS and while it is great i'm afraid that i can't use it at the moment. I will stick with the Original Realtek chipset for at least the initial Prototype as i have it setup and will think about switching to a Gbit Switch IC once I have confirmed the prototype works :D, I will need to see if i can get the schematics for a Gbit switch IC from Realtek as it appears they are the only ones i have found that do a 5 port gbit switch IC.
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visualecho
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Re: Multi Server CM Board

Mon Apr 27, 2015 1:41 am

amk wrote:Why use a two layer board?
I have a question...

I read the posts on the Compute Module Test Board, and I'm wondering what would *actually* happen if you had stayed with a two layer design? I'm designing a compute module board that's 80mm x 100mm, has no LAN chip, and also has the host USB connector on the other side of the board (for logistic reasons). The pair of traces from the compute module to the USB switch chip are about 80mm long. I've routed them as 12 mils wide and 18 mils apart with 20 mil spacing to the ground planes on the sides.

I understand the "matched length 90R differential pair" requirement. It's reasonable, justifiable, and *expensive*. CAD tools to do 4-layer work are often hundreds or thousands of dollars more. Prototype 4-layer PC boards are at least triple the cost of 2-layer boards from my favorite fab lab. I do my best to ensure the ground planes on my top/bottom combined signal/ground plane design is as contiguous and non-loopy as possible. I'm generous with top-to-bottom ground vias, I go over all auto-routed traces and make them 'islands' in the ground copper and without pointy edges. Previous projects I've done using high-frequency AC lines have never shown many problems.

My question is... "Why not use a two layer board?"

If I ignore all the warnings and paranoia, what might I expect? Calculations show that my expected impedance on the pair is about 88 ohms Z(odd), 176 ohms Z(differential). Assuming that the electricity on this low-voltage PC board is going only about half the speed of light, and that 80mm trace length is within the 100 picosecond requirement for USB 2.0, that this board is run inside a Faraday cage and a negligible amount of other EMF radiation is present... what? Will it work at all? The higher impedance melts the signal to zero? Diminished USB performance? Cold fusion detonation? International communism? It seems to me that the signal impedance match and ground impedance mismatch will result in a mildly distorted waveform but will still work... especially at a mere Full Speed (USB v1.1) connection.

Any thoughts? I know this is a reeally sloppy question, but I thought maybe I could get a little more insight from the forum. I'm guessing the best answer to this is, "Give it a shot!"

This won't be the final design, I fully expect to go to 4-layer for final production... *if necessary*. It might not be needed. Developing RF speed PCBs requires some trial and error, and I'm prepared for that, but I'm also keen on saving a bit of coin whenever possible. Thank you kindly for your consideration.

PS> extra special bonus points for Michigan State alumni, as the University of Michigan electrical engineers I've asked about this were clueless.

gsh
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Re: Multi Server CM Board

Mon Apr 27, 2015 5:45 am

If this is just for the USB signalling then I think you'll be fine, if you compare the quality of the traces on the PCB with the quality of some of the Chinese manufactured USB cables available in the world....

The main problems you'd experience when going to final production would be issues getting it through EMC testing... The two layer board will have no ground plane for the USB signals and therefore you'll likely have a return path for the USB ground currents that is not directly underneath the USB traces. This means it'll generate noise (which you'll see at 960MHz in the chamber), not sure how much noise but that'll be your main issue.

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Briarios
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Re: Multi Server CM Board

Mon Apr 27, 2015 5:50 am

Hello Visualecho,

tis a valid question you have hmm...

I had a look at doing a 2 layer board for the Test board. But after some investigation I had found that the traces for USB and Ethernet would be relativity large for the space I had allocated for it, therefore and after reading documentation about how to get the 90/100 ohm differential pair they had suggested to use a 4 layer board with the GND layer as close as possible to the signals.

Edit: gsh just answered the question :)
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visualecho
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Re: Multi Server CM Board

Mon Apr 27, 2015 10:20 pm

Beautiful... this is completely acceptable for my purposes. Thank you kindly for the responses.

> 960MHz
Ouch, I'll have to upgrade my Tektronix 475.

>with the GND layer as close as possible to the signals
Yes, I noticed that you got great results with a 0.2mm pre-preg layer. Seems kinda obvious now... use a 62mil dialectric, you need 50 - 60 mil traces :-) Every day I am so much less blind as to make ridiculous the coat hangers I used as welding rods the day before.

I won't hijack your thread any further, thank you again. Looking forward to your posts, Briarios!

Briarios
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Re: Multi Server CM Board

Fri May 01, 2015 12:04 pm

Ok Just to provide an update. I have sent my designs off to get a quote from a Fab house in China. So i am waiting on a reply, As they have a labour day long weekend this weekend I probably won't hear from them till at least Tuesday. :D
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Briarios
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Re: Multi Server CM Board

Wed May 20, 2015 1:11 am

Hello Everyone,

Sorry for the delay, I had to be in work/life mode for the last week 8-) but just to let you know I haven't forgotten about this and I am just letting you guys know that I have the Blank PCB's made up and they should be arriving in a week or so. once that is done I will then start populating one of the boards to test with :D
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Briarios
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Re: Multi Server CM Board

Sun Jun 07, 2015 4:26 am

Hey Guys,

Sorry about the delay, but most of the parts needed have come in :D so I am waiting on a couple of key parts which should be here by the end of the week. but for the time being here are some pictures of the PCB and Stencil and the small smd components 8-)

Sorry for the pictures the lighting was behind me and I didn't have another light source.

Front of the PCB
Image

Back of the PCB
Image

Stencil for PCB
Image

SMD Parts
Image
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RaTTuS
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Re: Multi Server CM Board

Mon Jun 08, 2015 8:21 am

that does look awesome
nice ;)
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Briarios
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Re: Multi Server CM Board

Mon Jun 08, 2015 8:42 am

RaTTuS wrote:that does look awesome
nice ;)

Indeed it does RaTTuS, Indeed it does 8-) ;)
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Briarios
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Re: Multi Server CM Board

Wed Jun 17, 2015 3:33 am

just a small update. I am waiting on key tools to build this board. I had hoped they would show up last week but nothing yet. Just to let you know I have all the parts and PCB's just now waiting on some tools to get this Prototype up and running. :? :?
http://rpi.pmfg.me -- Test board Eagle Cad Files.

Briarios
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Re: Multi Server CM Board

Tue Jun 23, 2015 1:49 am

Solder paste has arrived :D so I will be putting stuff together sometime this week and hopefully testing next week haha :D
http://rpi.pmfg.me -- Test board Eagle Cad Files.

Briarios
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Re: Multi Server CM Board

Sat Jul 18, 2015 8:45 am

Hello again everyone,

I have finally managed to put all the parts together, and unfortunately I don't have the steady hands needed for SMD soldering/re flow so there are lot of solder bridges that i can't seem to clear. here are 2 pictures of the finished board anyway so you can see on what my idea is about. At the moment I would assume that this board is not functional due to the amount of solder bridges. I will track down a company in Perth who may have the steady hands needed for this project.

TL;DR blaming hands not tools for bad re flow job :lol:

Front of the board
Image

Rear of the Board.
Image
http://rpi.pmfg.me -- Test board Eagle Cad Files.

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TonyD
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Re: Multi Server CM Board

Mon Jul 20, 2015 12:24 pm

A quick way of removing solder bridges is to use "desoldering braid" or "solder wick" which is braided copper wire. I use it all the time.

https://en.wikipedia.org/wiki/Desoldering
Tony

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cyrano
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Re: Multi Server CM Board

Wed Jul 22, 2015 6:10 pm

You use wick on smd parts? Man, you must have very good eyes and a very steady hand... :mrgreen:

What was useful to me was a fine pencil, with a well sharpened point. Graphite and solder aren't very friendly to one another. You can usually just push away the excess solder. And cleaning the flux off will also clean the solder balls left over from this process.

A visual inspection is still needed tho. And I need a good magnifying glass to do that.

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