I've a basic electronic question. Basically, I try to connect an Arduino proMicro(ApM) 32u with a RFID-RC522, classic situation.
The Pro Micro provide 5VDC and the RFID need 3.3V. Ok, it's work with the 5VDC directly from the proMicro, BUT, I want to understand what is happen.
So to realize my circuit, I start by simplify the circuit with 2 resistances, R1= 1K Ohm and R2= 2K Ohm, given to me Vref = (5V*2000)/(1000+2000) = 3.333333V. So, I'm proud of me, connect everything and it doesn't work .
Then I returned to my drawing table, take my multimeters and start to take mesurements. The VRef DROP to 2.3v when I connect the RC522 board. When I unplug it, my Vref is back to 3.3 :o
New Idea, what is the resistance of the board? In the specsheet of the board, the current used it's between 13 and 31 mA, my conclusion is I can calculate R of the board (Rb).
Too simple, I've said in my mind,
V = RI so
R = 3.3V/0.01415A = 233,2 Ohm or 233 never mind.
The new Resistance Req = should be 209Ohm (2000233)/(2000+233) , than the new Vref = 5209/(1000+209)=0.86VDC far away from my 2.3V
So I change my R1 and R2 by a factor of 100, so R1 = 100, R2 = 200, Rb = 233, (Req = 108) and Vref = 1.61.
Again, with R1=120 and R2 = 10KOhm, Vref = 3.2V.
I wondering if this is the good approach of the problem, I dont want to burn the chip... , impossible it work with Vcc (5V), but did I've the good approach to resolv this issue?
Any comments or proposition?