lightining 50 leds with arduino

Other Hardware LEDs and Multiplexing
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ttre

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Yes a transistor is what you need.
You can wire many LEDs with their resistors in parallel controlled by one transistor.

But turning 50 LEDs on and off is a bit boring are you sure it is what you want to do?

Also you will need a power supply and a transistor that will handle 50 x 20mA