I checked out your tutorial. Thanks for the excellent set of instructions! I believe I had ran across it before but I do not have internet service on my personal computer so I downloaded some tutorials and only half of that one downloaded! I got your example up and running.... It didn't want to work right at first but then I changed the Nextion's power source from my phone charger to the Mega and presto! I later powered both from my phone charger and it still worked.... So I suppose the essential part is starting both at the same time?
I had ran across the this example and tried it out... I used your improved code then I opened Dyspho's example and changed it to my screen size, and connected the RX to the digital pin 10 and the TX to the digital pin 11, but couldn't coax any results from it....