Hello there, So I'm about to connect a rgb led to my rgb shield (ka01) and as I dont wanna blow the led I'm here on some advice for resistors. So the rgb LED has the specs below, and rgb shield is powered from the 5v of the arduino. And as im a noob when it comes to calculating resistors I would love some help!
Specifications: Color: red (620-630 nm), green (520-530 nm), blue (460-470 nm) Luminous flux: 45 lm red, green lm 80, blue 20 lm Beam angle: 120 degrees Power: red 400 mA, green 350 mA, blue 350 mA Voltage: 2-2.6 V red, green 3.2-3.8 V. blue 3.2-3.8 V Max working temperature: 115 ° C Maximum ambient temperature: 60 ° C
The series resistor will have 5V - Vf across it, so calculate the value from that and the If
value.
Note you should calculate the power as well to see how big a resistor you need - series
resistors aren't efficient for high power LEDs, typically a constant-current boost or buck
converter is used to avoid wasting power.
Riva:
The shield you have does not look like a constant current supply that you really need for high power LED's like this.
Yes this is quite correct.
You can not use a resistor to control such a big LED at anything like the rated current. I would not use resistors below about 47R with any LED. If the resistor works out to be lower then a constant current supply is called for.
A link to your shield would be good, check the current rating of the outputs on that to avoid damaging it.
Thanks for the answers, So this is the shield Velleman KA01 RGB Shield for Arduino and according to the specs it can support up to 6a out on external power so it should work no?
hygea:
Thanks for the answers, So this is the shield Velleman KA01 RGB Shield for Arduino and according to the specs it can support up to 6a out on external power so it should work no?
It is not a constant current supply so is not really suitable. Have a look at this example of the type you need.
Thanks for the link, it takes so much guess work out of things.
So this is the shield Velleman KA01 RGB Shield for Arduino and according to the specs it can support up to 6a out on external power so it should work no?
Well only 2A on each of the three outputs and as Riva said it is not suitable for what you want. It is designed for running LED strips where the whole strip is the same colour.
So as I said you can run individual LEDs where the resistor is not too low, and lots of them if each LED with it's own resistor are in parallel, but it is not suited to a high power LED running close to its current limit.