So your shield works 100% on a Uno and Mega running the library examples.If you have a problem with your own code, please post your sketch and a schematic of your wiring.A simple pencil drawing of your wiring is fine if you attach a good photo.A written description of your wiring is fine too. But check it VERY carefully. The description in your message#13 is not accurate enough. Put yourself in our shoes. We do not know whether you have connected GND wires, what kind of power supply, what pins are connected ...David.
Why so complicated?You could supply the ESP8266 from the 3.3V output on the Mega. Of course the 3.95" shield obscures the 3.3V pin.Likewise, you could power the Mega from the 5V output of the MB102 and the ESP8266 from the 3.3V output.I am very worried about a 12V wall-wart. The MB102 regulator will get warm. A 6V or 7.5V wall-wart would be safer.The 3.95" shield takes about 200mA. Most current goes to the backlight.I have not heard anything about level-shifters for the ESP8266. If you drive it from the 5V Mega pins, you will back-feed voltage. You must have a level-shifter chip or resistors.We really do need to see a schematic as well as your code.David.
"Arduino UNO can provide only 50mA on 3.3V"150mA, Mega also. May not be enough for ESP8266 tho.
DC Current for 3.3V Pin50 mA