Arduino Robotics : Circuit Example

I'm new to Arduino and consequently, to circuits. I've been reading Arduino Robotics by Warren and this was a circuit present in the book.

From what Warren has said, electricity in the circuit travels from the negative pole to the positive, BUT to imagine it as going the other way for simplicity. So, looking at this circuit... it seems useless to have the resistor placed after the LED, based on the + --> - model. Wouldn't the LED turn on before going through the resistor, rendering the resistor useless?

Sorry if this seems like a basic concept, I'm entirely new to this.

  • 1
    So, this seems only very tangentially related to Arduino, being a beginner level electronics question. Should it be here? Mar 8, 2014 at 9:01
  • 2
    The OP got this question after reading Arduino-related stuff, so Arduino.SE is a natural target, although I agree this question would probably better in EE.SE
    – jfpoilpret
    Mar 8, 2014 at 11:12
  • @jfpoilpret Indeed it belongs in EE.SE. Actually, it's already there, so there's no point in migrating, in case anyone is thinking about that.
    – Ricardo
    Mar 11, 2014 at 12:42

1 Answer 1


Should the Resistor be Placed Before or After the LED?

The important thing to remember is that the direct current electricity must flow through the circuit to be useful. Since the resistor is part of the circuit (meaning that there isn't another path for the current to take) it resists the overall flow, thereby helping to protect the LED. Whether before or after the LED, it would still be in the circuit, and would therefore still reduce current flow.

Visualizing the Flow of Water

Think of it like a water hose, where the LED is a flow meter and the resistor is your foot. If you step on the hose before the flow meter it will cause the overall flow to slow down. Stepping on the hose after the flow meter but before the nozzle will have the same result, as the water must pass through the entire length of the hose before being released.

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