- Wed Jan 05, 2022 10:41 am
#93265
Hello btidey! Thank you for your reply and thanks for sharing that nice page.
And only a few months later I get back to this. but good.
I am doing the calculations for the respective pins of the RGB Led.
I have checked the ESP8266EX Datasheed page 24, electrical specifications and the max current for the I/O pins is 12 mA.
So for the red LED I have:
(3.3V - 2.2V ) / 0.012 = 92 ohm resistor
What's confusing me is that in the datasheet there is no value for the output max voltage, so I'm wondering in your calculation above, where you got the 3.3V from?
Also how would this work if the working voltage for the green Led pin ranges in 2.9V...3.6V?
Because in this case I may have a negative result for the resistor value:
(3.3V - 2.9V ) = 0.4V
(3.3V - 3.6V ) = 0V
(3.3V - 3.6V ) = -0.3V
so what is the correct working voltage to assume in this case?
Sorry if I'm making a fundamental mistake, I've been away from eletronics for a while.
btidey wrote:You should use a resistor for all leds irrespective of the colour. They do have different voltage drops but the current will not be well defined unless you use a resistor.
See http://lednique.com/current-voltage-rel ... iv-curves/ for some typical curves.
Blue needs the lower resistor value, green yellow a bit higher, and red the highest
Hello btidey! Thank you for your reply and thanks for sharing that nice page.
And only a few months later I get back to this. but good.
I am doing the calculations for the respective pins of the RGB Led.
I have checked the ESP8266EX Datasheed page 24, electrical specifications and the max current for the I/O pins is 12 mA.
So for the red LED I have:
(3.3V - 2.2V ) / 0.012 = 92 ohm resistor
What's confusing me is that in the datasheet there is no value for the output max voltage, so I'm wondering in your calculation above, where you got the 3.3V from?
Also how would this work if the working voltage for the green Led pin ranges in 2.9V...3.6V?
Because in this case I may have a negative result for the resistor value:
(3.3V - 2.9V ) = 0.4V
(3.3V - 3.6V ) = 0V
(3.3V - 3.6V ) = -0.3V
so what is the correct working voltage to assume in this case?
Sorry if I'm making a fundamental mistake, I've been away from eletronics for a while.
