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I am trying to minimize space usage for an enclosure that holds 48 boards with a RJ45 connector for Ethernet communication on each board. The boards work well with 10BASE-T (2 pairs) connection to a 48 port 10/100 Ethernet switch, faster is not really needed.

I am thinking of replacing the RJ45 with a much smaller connector, or with simple gold fingers and have an edge connector going on top - in best case even a backplane that connects to multiple boards at the same time (other end would still be 48 port Ethernet switch though for the time being).

Would this work or do you have other recommendations?

(objective is shaving off the height of the stacked boards, keep noise at minimum, and avoid connecting one by one if possible)

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    \$\begingroup\$ The gaps between the boards would be smaller than, say 10mm (height of the RF45). You may end up having a dickens of a time arranging air flow in narrow gaps like that. What's your approach to thermal? Just my $0.02 worth. \$\endgroup\$ – Nick Alexeev Apr 15 '13 at 1:21
  • \$\begingroup\$ @NickAlexeev - If he only needs 10BASE-T, I doubt there is that much high-power processing going on. \$\endgroup\$ – Connor Wolf Apr 15 '13 at 9:17
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In theory, you could get a custom cable to go from RJ45 to anything you want. Samtec has some great connectors. The only thing that (supposedly) matters is the pairs being twisted to prevent crosstalk between the pairs. However, if your cabling is very short, it might not matter as much, especially for 10BaseT. You can probably use an old-school 0.1 pitch connector for that.

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If the deployment is in a controlled environment (no random people plugging random cables into connectors), you could consider what is probably one of the most ubiquitous low-profile connector around today, the micro-B USB 2.0 connector.

The advantages are price, size and a likelihood of sustained availability: Those connectors, and cables to connect to them, are very common with cellphones, so standardization is high, as is volume-driven price reduction over time.

Those connectors are available in both flat and vertical configurations, so a backplane option becomes viable, or better yet a riser board or several of them.

The big disadvantage is that someone could conceivably plug a cellphone charger into one of the ports.

For a very short cable run to the actual RJ45 ports as specified in the question, cable impedance and twists-per-inch may not be deal-breakers - OP will have to check the actual deployment constraints to determine this.

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Make 2 variants of the board - let's call them Master and Slave. Master has 2 (or 3) RJ45s, Slave has board-board connections to the extra sockets on Master.

Master can accommodate a Slave on either side of it if you need to triple the density.

However as Nick says, you will have to pay close attention to cooling and airflow.

And it implies removing a set of boards - Master + slave(s) rather than individual boards for maintenance.

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Another option is four conductor TRRS jacks and plugs, with standard ethernet cabling.

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