Learning from my experience with a 168Mhz MCU interfering with a 180Mhz DC/DC I realize that I might need a similar option to separate the 4V PSU feeding the SIM808 on the module pictured above. In this case I would need a larger 2-3A coil related to 13 (4V PSU) above. This being a single side assembly I will add an optional connector for this on the back-side just in case.
Ethernet (W5500) already have a coil separating it’s 3.3V from the MCU.
Raspberry PI Zero W also feed from the same 5V – I need to add a coil option for this as well. What I will do is to add a connector that is shorted so that I can cut this and introduce an inductor if needed.
The last one is the 3.3V for the MCU itself. It feed from a 5V PSU that will feed several cards all running a 168Mhz MCU. I hope the linear regulator will do the filter job, but I will add an optional coil here as well – just in case.
I might also add some scope test-points + I will re-examin the SIM808 design – but after that I will order the PCB so I can start. I have to be realistic and expect that I will need 3-4 revisions before this module is working properly due to it’s complexity. I have evaluations boards we can connect to play with SIM808 SW – I actually need to get a new subscription with a few SIM card’s for testing.