@AhtishamAshraf The mosfet siwtch using irl540n seems working with input 5V. However, I found 3v3 input does not work. This surprises me, because I tried it before and found it OK. Perhaps my irl540n is fake. I am thinking of using optocoupler EL817C shift up 3V3 signal to 5V. Or I should shift it all the way up to 12V, because 12V is readily available. So we are hitting two birds with one stone: (1) level goes up, and (2) noise comes down.

@AhtishamAshraf Now I have forgotten how the bias EL817. I vaguely remember If = 5mA should work, but 10mA might be better, and 20mA is maximum. So let me try 10mA. R = (12V - 0.6V) / 10mA ~=11V / 10mA ~=1k1. So I shall try using 1k1 as the limit resistor.

I honestly don't have much idea about these calculations i am a programmer LOL @tlfong01

@AhtishamAshraf Don't worry. I forgot to tell you that you can just sit back and watch, and just go away don't you software debugging on RFID, and come back a couple of days, and see how I am getting on. Actually this replace-relay-by-mosfet-switch is a common trick in dc motor and solenoid applications. In other words, my suggest circuit if proved good, could be used in magnetic lock, electromagent ic lock, and motors as well.

If my test is good, then I will try to draw a proper schematic for newbies to just follow the schematic and solder the chips together.

And if my mosfet switch does not work, you can just stay with your relay switch, and hope that the trouble is on RFID code, not related to any hardware.