# electrical diagram explanation

Hello,

I’m a novice in Arduino and in electronical things in general and I have a question:

I did this

it’s working, but I don’t understand why…

Because after calcul the Red Led should receive 6mA only…

We have RA=220Ohm and RB=220Ohm

RBlueLed=(U-UBlueLed)/IBlueLed = (5-382)/0.2 = 54 Ohm
RRedLed=(U-URedLed)/IRedLed= (5-1.93)/0.2 = 140 Ohm

R2 = RBlueLed + RB = 54+220 = 274 Ohm

Req = R2RRedLed/(R2+RRedLed) = 93 Ohm

U2 = UReq /(Req + RA) = 554/(220+93) = 0.86 V
I3=6mA

Am I wrong ? Can you explain ? I’m lost!

I think your decimal places are screwed: I of an led is 20mA, which is 0.02A not the 0.2 you seem to have used.

JimboZA: I think your decimal places are screwed: I of an led is 20mA, which is 0.02A not the 0.2 you seem to have used.

And: 6mA will make an LED light up. Even way less than that will make it light up. It will be dim, but it will light up. Try a 1 kOhm resistor, it will still work. Also, the resistance of a LED is best looked up in the datasheet. LED's dont work like a resistor, as their resitance is not very linear.

pbrouwer:

JimboZA: I think your decimal places are screwed: I of an led is 20mA, which is 0.02A not the 0.2 you seem to have used.

And: 6mA will make an LED light up. Even way less than that will make it light up. It will be dim, but it will light up. Try a 1 kOhm resistor, it will still work. Also, the resistance of a LED is best looked up in the datasheet. LED's dont work like a resistor, as their resitance is not very linear.

Good luck finding a LED's resistance in a datasheet, because such a specification does not exist. Perhaps you meant to look for the LED's forward voltage drop (Vf) in the datasheet?

Lefty