Hello,
I would like to connect 4 RFID RC522 sensors and a screen TFT 2.8" on a MEGA powered directly by its 5v pin. Do you think it will resist?
I wouldn't expect it put up a fight
It has plenty of resources, including 2 hardware UARTs
I was sure too, it's why prefer to use 2 Uno 
Thanks
How will the Unos communicate with each other ?
By serial, I just tried , it works ^^
What is the advantage?
Two processors are better than one
When the screen is connected with all the sensors on the same board, all seem slower, the screen blinks and not all sensors work correctly.
Another way is to use a kind of STM32
When the screen is connected with all the sensors on the same board, all seem slower, the screen blinks and not all sensors work correctly.
I would expect the the Mega be able to drive them all with no problem. I would be interested to see the code that you used. For instance, the screen blinking is typically a sign of sloppy programming
Wally06:
Two processors are better than one
...when they are on the same board, then I will agree.
I don't think the code of my games is sloppy because all the sprites display fast, move even on a background:
But when I connect the 4 sensors, (even without adding any code) the screen blinks very slightly, like if there's not enough current. So, I prefer don't take risk to burn all.
Thanks for your comments 
I do trust you mean that you have a Mega 2560 which is powered by a proper 5 V regulated power supply which supplies it by the "5V" pin and also connects to all the other individual attachments.
A Mega 2560 is itself meaningless as a "power supply" - it cannot supply power to other devices.
The problem with using two processors is that they will need to communicate with each other. If they do, then you have to develop a communications protocol and that protocol becomes another function of the state machine. That makes things quite difficult as you have to continuously monitor the serial (or other) interface for new information/ instructions from the alternate processor. Not a trivial matter by any means.
I just was curious to connect all on MEGA but 1 RFID is about 20mA from what I read and the screen draw many current too, then I would like also add some LEDs...
My sensors was not powered directly by the power supply but from the 5v pin. I will try to change it.
By the way, with SerialSoftware, I just have to send and receive bytes that my code can interprete as its own instructions. That's fast, all is ok, it works perfectly between Uno-Uno and Uno-Mega. Plus the wiring is more clear
Please post your code here so that it can be copied to an editor for examination
No need, the problem was what you said, a fight between SPI of the screen and all the Rfid, now all work perfeclty.
Thanks for your advices and Happy New Year!!!
I finally didn't have time to make that MASTER MIND on Mega, so I stayed on 2 UNO but it works fine too:
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