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Topic: second led to the circuit (Read 284 times) previous topic - next topic


hello, i am beginner in arduino. i have knowledge in electric circuit and associated parts. my question is when i want to connect second led as serial to existing led , leds dont illuminate. could you please explain why they dont work? do i need to reduce ohm? here is my circuit subparts:


1 ea resistor 333ohm,
1 ea led
5V digital output from ardunio


Oct 13, 2019, 10:15 am Last Edit: Oct 13, 2019, 10:17 am by Grumpy_Mike
second led as serial to existing led
There is not enough voltage out of the Arduino to power two LEDs in series. The voltage drop on an LED depends on its colour and you don't stand a chance of doing it with anything but a red LED. Even then it might not work depending on the material it is made from.

Wire another LED and resistor in parallel and up the resistors to 470R to keep the total current from the pin down.


thank you for helps. now it Works.one important note that i have 3 color led, red, yellow, green. red and yellow illuminates but green doesnt in paralel connection. very interesting.


No not interesting at all. You have to use three resistors not one in the common connection. If you do then the LED with the lowest forward voltage drop prevents he others form seeing a higher voltage and so they won't turn on.

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