multiple MFRC-522 conection in paralell with external batery

hello, im trying to conect 3 rfid modules to arduino uno (with the usb cable), to read some data from de keys. im using the example “dumpinfo”, which is in the library, to check if the work properly. While i was using the 3,3 v pin, and de respective pins for the SCK, MISO, MOSI, and GND i didnt have any problem, everything was working fine. The problem is, that i dont have avaiable that pin(3,3v), because i burn it. So, i use the LM3940 (a regulator with his capacitors), to convert the 5v from an external font, into 3,3. The voltage now is good, so i connect this three modules in parallel (with the SCK, MISO, MOSI, to pins 13,12,11). But they dont work. Even if i connect one module only, it doesnt work except if i connect the negative pole of the circuit to the arduino GND. I dont understand why do i have to do this, and i it doesnt work if y put another module in parallel. i dont now if the board is broken or is just that arduino has to be always connected to ground, but i dont find it logical.
thank you for reading!

You need to understand the concept of an electrical circuit.

Unless you connect the grounds of the different parts of the circuit, the current cannot flow.

i Know what is a electric circuit. what i didn't understand is why with an external circuit, the arduino needed to be conected to the ground of that circuit. but i solved. the problem was the ATEMEGA328, it was broken