Why Samtech connectors????

[osteth]

I am just wondering why an expensive and proprietary connector like the samtech connectors were chosen for this over something like a PCI express connector? or better yet just put pci express board edge connection on one side of the board and you have 67 available pinouts more that 4 samtechs. it is also vastly more available and at a lower cost. just wondering?

[osteth]

Just an edit: I misspoke to the number of pins on the samtech connectors I was thinking GPIO pins not actual pins on the connectors, but the question im asking still stands as to why a more available connector was not used in favor of a very dificult to attain one.

[9600]

This is not an official answer — that would need to come from Andreas, Fred or Graham — but my guess would be that footprint/profile/density was a major factor. PCI Express is a lot bulkier and also means you end up with either two boards at 90 degrees to each other or else side-by-side, and either way taking up a lot more space than two similarly compact boards sandwiched together and with ~5mm between them.

Regards,

Andrew

[xilman]

[9600]

Hi Paul,

I'm afraid I don't know.

Personally — and this is pure personal opinion, again — I'd favour some sort of PCB backplane. Of course, this would clearly take up more space, but I have an aversion to cables in general (looking behind a desk or workbench at them tangled up actually makes me queasy!)

Cheers,

Andrew

[osteth]

I guess that makes sense, I guess all the design files are open source so If it REALLY bugs me I could always just reroute things however I please... and then make a backplane... But then Id be all off on my own fork and things get all kinds of hectic when you deviate too far from the source.

[aolofsson]

Thanks for the feedback.
Why do you consider it expensive?
What are you building and what is your goal? A commercial product?

The BSH samtec connector was chosen due to combo of:
-low price (in volume, 1K+)
-low height
-high frequency
-density (240 pins on credit card size)
-mechanics

Andreas

[osteth]

I find it expensive because it is $6 per (1 unit break price, I know that there is a discount at 1k and a discount via buying through a CM commencerate to the CM's yearly spending with each distributor)
Which means that on the board with 4 of them there is $24 in just connectors (+/- discounts) and wile each of them has 240 pin and only 48 of them are actually used meaning 912 pins are unused.
By elimination the connectors and switchon to a 52pin pci express board edge connection it would allow the same ammount of GPIO pins, remove the connector cost from the board almost entirely (minor additional costs for the board manufacturing) also, since the board needs to be vertical for fanless operation a backplane for connection mulitple boards would be completely ideal in a configuration like this and the connectors for the backplane are sub $1.

After looking at connectors for a bit I have only found one downfall to a doing a pci express board edge connection in to a socket such as this: http://www.digikey.com/product-detail/e ... ND/1002341
and that downfall is that it would limit the connection to 5gb/s in each direction. (requires gen2 pci express for 5gb/s)

the samtech connectors are fantastic connectors on paper for sure. but I personally just feel that in practiacl application that are overkill for the task and dificult to source in hobbyist/research quantities due to a low level of addoption in COTS products.

[aolofsson]

Thanks for sending the link to the digikey part. I did not know that the pcie sockets were that cheap in single unit quantities!

Absolutely agree that for any low cost application, a SOM with a pcie or SODIMM edge connect is the way to go.

If you are trying to save cost and don't need all the pins, you don't have to populate all the connectors, you could get down to 1 or 2. Not sure I see a valid argument for the research market in saving $6 for 1-10 units?

If the Parallella volume gets high enough we would certainly consider producing a SOM like the raspi folks did. Of course, since we are completely open source you could always grab the source and build your own board at any time.

Andreas

[osteth]

Absolutely, there is no significant reason to do a full overhaul of the baord to save $6 at low volume, over using what is currently working. I just was just highly currious as to the origin reason of the choice of these connectors. I was questioning it because I was attempting to come up with a good case for a 24 node clusterand was trying to figure out how best to mount, power, and structure the cluster while keeping the units vertical and keeping the elink ports accessable. With these connectors (on the bottom) the units are very easy to work with in the horizontal possition but the requirement of mounting them vertically for fanless operation make the entire design dificult to work with.