In this latest iteration of the basic design, the large PCBs from PCBWay were stacked 2 high as shown above, but if we count all the PCB layers, there are about 7 in total which will give a total of 12 LoRa radio modules. But this is not the end of it, more of the large custom PCBs can be added to extend the LoRa modules by 6 for each PCB added. This entails A LOT of 3mm brass stand offs and USB hubs and very kindly, Liam at PCBWay sponsored this project by supplying these aforementioned components and the large PCBs  for free. Thank you Liam !!! Nonetheless, the LoRa modules are quite expensive, as are the 'MEGA 2560 PRO Embed CH340' modules that control them and so I chose initially to test on just four modules working simultaneously which should also make programming a bit easier to start with. I also had a bit of a scare with the  MEGA 2560 PRO modules as in one batch about 50% were defective. Fortunately, this problem was solved by simply removing one of the 3 pronged voltage regulators which got crazy hot after a very short time. If anybody else comes across this problem - just remove the component that gets hot with a soldering iron. Obviously the module can no longer be externally powered other than by USB or 5 volts, but this project does not need to do this.

Getting back to the Layer Cake, on the bottom we have one of the large custom made PCBs from PCBWay. The next layer is the MEGA 2560 PRO modules which can be seen and the Master Rasperry Pi and the MPS 8A 5V power supply which both cant be seen in this photo. The 3rd layer up is another large custom PCB and the 4th  the LoRa modules which are at the same level as the slave Raspberry Pi. 5th layer is a 5 way USB hub. The 6th a Raspberry Pi to Arduino footprint adapter and the 7th layer a fancy Ublox F9P GPS module. These layer cakes are in pairs and there is one, with the joy sticks fitted, that sits in the control room, or 'Nest'. The other requires no joy sticks and sits on the machine, the 'Dog', wherever that might be. The whole point of this project is to get correction data transmitted in parallel from the Nest to the Dog ..... so the next challenge to to upgrade the software with some parallel processing!