As an arduino teacher I have faced that making someone to connect more that one component for the very first time is very frustrating.
So I decided to tell people to connect the leds without a resistor. If powered with 5V from a digital pin from an arduino, the led can burn. But as the very first lessons are blink and all its derivates, nothing goes wrong because it is not powered 100% of the time.
Luckily a few lessons ahead we worked with RC servos and thanks to the mistake of a pupil, I discovered a fantastic trick: don´t declare de output pins!!!! this way arduino will only put something around 3V in the pin when using digitalWrite.
Every time I use leds, I wire them directly to a digital pin without any resistor and they work fine. Just make sure you don´t declare the pin as an OUTPUT with pinMode!!!!!
Have you tried?
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