In the previous update we took a look at how the 32+1 node Circumference 100 has evolved from the very first prototype — which used a great deal more cabling and an external power supply — to a highly integrated solution built around a custom backplane. However, we didn’t really give any detail on the backplane itself and how Raspberry Pi compute nodes are connected.

The above stop frame animation shows clearly how a stack comprised of 8x Raspberry Pi boards plus backplane is assembled, with each compute node securely attached to the backplane via high quality Samtec connectors, and separated by four M2.5 black nylon stand-offs. This sub-assembly is then secured to an acrylic plate which has had two 5-port Gigabit Ethernet switches attached.

With the C25, two Ethernet cables run direct to the UDOO dual-gigabit Ethernet adapter. While with the C100, there are 8x Ethernet cables that run into the base and connect into an additional two 5-port switches, which in turn are connected to a dual-gigabit Ethernet adapter. In both cases the only other connections are 1 or 4 each of USB cables for control, and 6-pin PCIe connectors for power.

So as you can see, it’s a pretty neat solution in terms of cabling.

Andrew and the Circumference Team