Electronic – Arduino Question regarding the resistor


I was instructed to set up a resistor on the negative side of the LED and pulling it to ground. I'm confused why we are implementing a resistor on the backside (negative end) of the LED. I always thought we put resistors before our load (LED) to limit/control current flow. Therefore, I'm confused why we are putting the resistor between the cathode (negative end of LED) and ground. To me it seems like this resistor isn't doing anything.

I don't know if it helps but on my board the positive side of the LED is connected to PIN 13 and the negative (cathode) end is going to the resistor then to the ground on the breadboard then to the ground pin on the Arduino board.

I apologize for the picture as it's the best I can get it at the moment with what I have available to me.

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Best Answer

While driving a load with a microcontroller, you may add resistors on either side. This is because the current entering the LED and leaving out of the LED is the same. So if a resistor is used on the high side or low side, it would limit the current. They can be used on either side and either way because they are not polarized.

In such configurations, resistors limit current flowing through an active component (LED in your case). Considering Kirchoff's Law, it doesn't matter if the resistor is on the positive or the negative side of the LED. It would limit the same amount of current irrespective of the positive side or negative side of LED.

More reading: Kirchhoff's Laws