Hello everyone, I am a beginner to Arduino and getting some issue while configuring the RFID RC522 with my Arduino board.
I am getting an error which says "WARNING: Communication failure, is the MFRC522 properly connected?"
After reading some already closed posts on forum and researching on YouTube I ended up finding this video which suggested to power the RFID receiver from Vin pin instead of 3,3 V Pin on Arduino . It worked and the receiver could detect the Tag, so I am sure that the issue is not wiring connection (as many posts suggested to solder the wires). But what I do not know is what the Vin pin actual does?. I understand that it could be used to power Arduino but I do not know if it could also be used to take output voltage from Arduino too?. Is the Arduino routing the input power which it is getting from USB to Vin? Is it safe for the both Arduino and RFID board to use Vin as an input to the RFID receiver?
At the same time I am still unable to understand why my RFID receiver originally doesn't work when I put it on 3.3 V.
Any inputs here would be of great help.
Welcome to the forum
The name of the pin gives you a clue as to what the pin does. In English I would read the name as V in, ie voltage in
It is connected to the centre pin of the barrel jack on the Uno so if you were inputting say 12V to power the Uno you could use either barrel jack of the Vin pin
How are you powering the Uno
Hi, Thanks for the reply. Ofcourse I unterstand that it says voltage input 
. My question was , what else could be done with this pin. As in my case the input voltage to Arduino is coming from the USB and when i followed the youtube video (that asked me to use Vin to supply 3,3 V to the RFID board, which worked). It opens up the question if this pin could also be used as an output?
If yes , Is it safe for my RFID board? As it supports input voltage of 3,3 and 5 could damage my RFID receiver.
The Vin pin can be used as a voltage output but that is not what it is designed for. There is always the possibility that you will put 12V into the barrel jack and get 12V out of the Vin pin thus damaging whatever you are powering from it. My advice would be not to use Vin for anything other than its intended purpose as a way of supplying voltage to the board
If you need to power an external device then use the %v or 3.3V pins on the board if the current required is low, say below a few mA, otherwise power the external device from an external power source entirely
Why not power your RFID board from the 3.3V pin of the Uno ?
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Thats what i am originally trying to do. Taking 3.3V directly from Arduino board but somehow the Serial monitor shows communication error and the RFId receiver won’t identify any Tag. Any suggestions on what else could be the issue?
Please post a link to the RFID reader that you are using