I have the following leds ... enter image description here ... that I hope to be able to connect to my pi for power and disk activity indicators.

I read some guide that claimed that around 330Ω resistors were needed, but the small board I have has one 33Ω resistor per each two leds.

The color stripes of the resistors are orange, orange, black which I understand to be 33Ω, I also measured them and got 33.4Ω.

I realized that my multimeter could measure the forward voltage, and I got 1.63V. Then I would get (3.3V - 2*1.63V)/0.016 = 25Ω. Or in reverse with a 33Ω resistor the current would be 12mA if I have understood this correctly.

Will that be fine?

( I am also a bit worried about that it being two LED in series, with what I measured 3.3V-2*VF is rather close to 0. )

1 Answer 1


No one can tell without a specification - I have never seen anything like these before. It depends how the LEDs are wired.

From the rather poor photo the resistors seem to be 22Ω.

The Pi GPIO can safely supply 16mA so anything over 120Ω (3.3V - 1.3V)/0.016 will not damage the Pi.

NOTE LED voltage varies from 1.3V to 3.6V (depending on colour) the value I used gives a “safe” result.

Series LEDs may not work reliably with the Pi and current world be unpredictable.


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