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RGB LED Newb Question
Nephasth:
--- Quote from: wxforecaster on October 15, 2013, 04:41:04 pm ---Folks, Google is your friend. The resistor goes between the supply voltage (+5V) and the cathode. There are 3 cathodes on an RGB LED, one for each color. Please read my post again. A resistor on the exiting anode lead connecting back to ground is not what you want. It's not going to harm anything, but your LEDs won't operate correctly.
--- End quote ---
Did you know that there are two types of RGB LEDs? Common cathode and common anode. So it really depends on what type you're working with, but the most common type in this hobby is common anode since most LED controllers we use control the ground side of the circuit. In either case, positive voltage gets connected to the anode (the "entering" lead), not the cathode. You've got it backwards. ;)
With a single color LED, it doesn't matter which side the resistor is on (but it does matter which side you apply positive voltage to). But since an RGB LED is three LEDs in one, the best practice is to install an appropriate resistor on each cathode of the RGB LED.
Edit: This is from your friend, Google:
wxforecaster:
You are correct. I would not have expected anyone to buy a common cathode RGB LED from any of the arcade sources, but you're right, someone could also just pick up a load of them on Ebay on the cheap in which case you definitely need to be aware of which type you are dealing with. Great followup post.
AndyWarne:
Whether or not you need resistors is dependent on what you are driving the LEDs with. If its a constant current source such as our PacLED64 board you don't need resistors at all.
If its a non-current limited source, as has already been noted the values of resistors might need to be different for each channel. One way to get an exact white balance is to connect pots to each channel and adjust so that the current draw of the highest channel is within spec (usually 20mA) and the white is actually white, then measure the pot values and fit resistors.
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