So, it appears that people have issues because the 5V regulator on the arduino mega burns out trying to dissipate 12V. So something I am going to try is just adding a 7805 directly to the RAMPS board and feed 5V power to the mega directly. So, instead of
+12V -- D1 -- Vin
I will have
+12V -- D1 -- 7805 -- AM-VCC
|
GND
A TO-220 7805 should be able to dissipate the heat from 12V easily compared to the surface mount regulator on the arduino board.
I checked the mega schematics, and it appears to be able to handle being provided with an external regulated supply just fine, it regulates the 3.3V supply off of the 5V one and has a power mosfet protecting you from reverse driving the USB port.
Has anyone tried this? It would be nice to get this into RAMPS 1.4, having to power the arduino independently from the shield seems like a pain.
John