I want to replace an RGB LED controller (much like this one) with my own MCU.

Therefore, I think I need to know what voltage(s) the RGB LED controller outputs so I can make my MCU/component have the same output voltage(s). Then I can control the colours with the MCU.

The RGB LED controller has a 12V input, and a 12V + R + G + B output that connects to an LED driver unit.

Unfortunately, I currently only have a basic knowledge of circuits. I have a DC power supply and a multimeter, how would I go about finding out what voltage(s) the RGB LED controller outputs?


Edit Here's the lighting circuit I have

  • \$\begingroup\$ Those things are too dumb to output anything other than 12V. \$\endgroup\$ Commented Sep 3, 2015 at 14:19
  • \$\begingroup\$ @IgnacioVazquez-Abrams: Fair comment, but how could I measure that that is the case? \$\endgroup\$
    – parrowdice
    Commented Sep 3, 2015 at 14:34
  • 1
    \$\begingroup\$ More importantly, what are the LEDs? \$\endgroup\$
    – Andy aka
    Commented Sep 3, 2015 at 14:48
  • 1
    \$\begingroup\$ Yeah huh! I can read your question but, not all cup-cakes are identical just as not all RGB LEDs have a common specification (data sheet) written in stone that every self-respecting engineer knows about. \$\endgroup\$
    – Andy aka
    Commented Sep 3, 2015 at 14:56
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    \$\begingroup\$ First supply the LED specs (or links to them) to see if my suspicion is correct. Here's a clue - supplying exactly the same voltage might be trickier than you thought BUT I can't be sure without the specs of the LEDs. \$\endgroup\$
    – Andy aka
    Commented Sep 3, 2015 at 16:19

1 Answer 1


The controller outputs 12V (likely passes the input straight through), and sinks/grounds the R, G, & B pins through a n-channel mosfet or bjt transistor. There is very little voltage drop present from the controller's active component. All it does is opens/disables the R, G, & B pins (leaves them floating) to turn the leds off, and closes/enables them (connecting the path to ground) to turn the leds on. It uses PWM to adjust brightness and color.

Typical insides:

Google "RGB Controller schematic" for plenty of ideas on how to implement your own. You could even cut the circuit in your controller up to remove the microcontroller while keeping the driver section.

  • \$\begingroup\$ Thank you Passerby, much appreciated, that's exactly what it's doing. Are there any advantages/disadvantages to sinking the RGB pins directly through the MCU, vs. sinking through a transistor (the current is about 1mA per pin)? I tried sinking directly through the MCU and it works. I can now control colours/brightness. I can't see any downside yet. With your experience, do you know any reason why that would be a bad idea? Thanks for your time and help. \$\endgroup\$
    – parrowdice
    Commented Sep 4, 2015 at 10:22
  • \$\begingroup\$ @parrowdice No, bad, warning. Your MCU is 99% likely to not have 12V tolerant pins. Are you talking about the mosfet/transistor gate/base? That's fine. But actually connecting the leds directly, that's a big no. The led ring you show is most likely a few hundred milliamps, maybe an amp, not 1mA. \$\endgroup\$
    – Passerby
    Commented Sep 4, 2015 at 10:27
  • \$\begingroup\$ On the RGB wires coming from the LED driver that I connected to the MCU, I'm pretty sure I measured around 1mA @ 1.7V using a multimeter, which is why I thought it was a reasonable idea. I'm sure I could have measured incorrectly though. I'll triple check when I'm home... Thanks. \$\endgroup\$
    – parrowdice
    Commented Sep 4, 2015 at 11:00
  • \$\begingroup\$ I've just measured, the current on the RGB outputs is definitely 1mA @ 25mV. The LED driver has a ground connection which has ~200mA through it. I'm not sure about the internals of the LED driver, but it should be okay to sink the RGB outputs directly through the MCU, right? Thanks \$\endgroup\$
    – parrowdice
    Commented Sep 4, 2015 at 16:38

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