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Design of remote monitoring and 'pluggable' PCB standards

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philbx1:
Hi all,
Just me thinking again, and thought I might ask if there is a miniature 'standard' in pluggable
PCB's that is more prevalent in compact portable applications.

I've seen mention of the Eurocard and PXI standards in the Open Source multimeter discussion
but have yet to find a 'standard' that uses minimal space.

Basically what I'm after would have (for instance) a backplane of maybe 60 x 30 mm, a horizontal 'main board' oblique to this of maybe 25W x 50L mm, and various vertical module PCB's being
25H x 50L mm.

These 'modules' (IE. battery monitoring, FET, gyro, temperature etc.) can use any standard protocol, but I'll be leaning towards I2C as I think (maybe wrongly) that it's pretty much a microcontroller standard now.

If this is all a bit confusing I might just try using Sketchup to show you what I mean, although that's
a painful area to go to after trying it out for a while now..

Anyway, your thoughts are much appreciated.

daedalus:
I2C is fine, but there are a few things you need to consider if you want to have redundancy, failover, and / or hot-plugging. Have a look at some of the TI I2C hub and buffer chips, the datasheets cover problems like what to do if a daughter board has a fault on i2c pins, how to handle correct start-up on hot-plug, etc. Its worth a browse even if you don't use their chips.

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=1651&uiTemplateId=NODE_STRY_PGE_T

philbx1:
Hey there Daedalus,

Thanks much for the reply. I was thinking this was all a bit too much to ask from our forum
but you've given me some great info.
BTW, I'm currently looking at Samtec Edge Card connectors etc. which look pretty neat.

And yes, your thoughts on I2C protection will mean a lot with my design.
Again, thanks.


--- Quote from: daedalus on October 10, 2011, 10:04:40 pm ---I2C is fine, but there are a few things you need to consider if you want to have redundancy, failover, and / or hot-plugging.

--- End quote ---

ejeffrey:
Standard is hard to reconcile with compact, especially if you want rugged, flexible, simple, and cheap.  Increased integration and lowered cost of fabrication has also reduced the demand for such a thing: The cost of a backplane + connectors + multiple PCBs + an enclosure that supports pluggable modules has to be weighed against the cost of just building everything you might want on one PCB, and rolling a new revision if you discover a new sensor you want. You don't even need to populate chips you don't want to use, just put a footprint in.

So you generally only see backplane standards where end-user customization is absolutely necessary, and/or the per-module cost is fairly high (see PXI).  Otherwise you usually just see ribbon cables or flat-flex cables running serial protocols between boards when necessary, or people roll their own with only the pins you need.

Possibly the closest thing to a standard in the small(ish) form factor is the arduino stackable shields.  Not all shields play nice, but if you stick to I2C/SPI + power you shouldn't have any problem.

philbx1:
Hi Jeff,

Thanks for the input, again much appreciated.

Although I was thinking as a 'product' simple boards could be added for whatever purpose and have the base-board
available without too many board upgrades.

Maybe an arduino 'mini-board' spec will appear in future?

You are right though. Maybe too much thought and probably not enough action :-)


--- Quote from: ejeffrey on October 13, 2011, 09:54:58 pm ---Standard is hard to reconcile with compact, especially if you want rugged, flexible, simple, and cheap You don't even need to populate chips you don't want to use, just put a footprint in.

So you generally only see backplane standards where end-user customization is absolutely necessary, and/or the per-module cost is fairly high (see PXI).  Otherwise you usually just see ribbon cables or flat-flex cables running serial protocols between boards when necessary, or people roll their own with only the pins you need.

--- End quote ---

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