My KiCAD skills are coming back – just a quick check on the Ethernet module. I reduced MCU to LQFP48 and used a W5500 module through headers. I moved drill holes to the corner. The J45 in the middle is just for show. This is a 25mm x 45mm module and I will have plenty with space by the looks of it. This is good news. I need to squeeze in a x-tal, SWD connector, CAN Tranceiver and connector, but that’s doable. To squeeze in FRAM – not sure, in which case I store config on an internal flash page. My Ethernet to Serial modules from AliExpress are smaller than this, but I got a STM32 I can program and mounting holes 🙂
I will make one module using the W5500 adapter shown above – hence the pin header. On a later module I will use a low profile RJ45 and W5500 or W6100 chip directly – or I could use a MCU with an Ethernet interface. W5500 will give a max of 15Mbps speed. With a backbone bus of 5Mbps that is more than sufficient.
Above is a comparizon of some of the PCB sizes I can use. On top the Ethernet Module with the size of a LQFP64 outlined outside the LQFP48 footprint. In middle a dual width (90mm) module and at bottom a dual height (50mm) module. This is just to give a brief idea of how much space that is available for IO. And the beauty of this system is that I can continue to scale up.