Conecting a relay - General Electronics - Arduino Forum

I've noticed in several pictures that a relay is controlled by the arduino by connecting the 5v arduino pin to the relay and the ground is connected through a transistor, with is controlled by another pin on the arduino. In other pictures I se that a normal output pin from the arduino is connected to the relay, and no transistor is used. What is the difference between these two approaches. Is there an advantage in using the transistor, or are these just two ways of doing the same thing? I put tw

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