Double click on the picture to see the larger version …
The SIM800C uses a 4V PSU that need to support 2A. All the circuitry on top is PSU related according to reference – I have removed some, but need to see the PCB layout before I consider the rest. Also, I am not sure I bother With the USB Interface. But, well it’s an ealy draft anyway…
I have not Connected the voice on the Ethernet module due to Space concerns.