I built an RGB LED strip controller with a Wemos D1 mini, using this schematic:

enter image description here

On the phone I have a color picker and just roll over it and the LED color changes accordingly, but sometimes I hear a whining noise (not from the 5V regulator, but from the power supply) and another strange thing is when I measure the voltage between red LED and 12V (I get something around 5.6V) but I should measure 12V, because this is what I measure on green and blue LEDs. I measure this value even if the code from arduino IDE is "analog write 255 -> RED LED, and for GREEN and BLUE is 0".

  • \$\begingroup\$ LED data sheet is required. Power supply data sheet is required. \$\endgroup\$
    – Andy aka
    Commented Oct 11, 2020 at 9:25
  • 1
    \$\begingroup\$ And a clear marking at which points in your schematic you measure \$\endgroup\$ Commented Oct 11, 2020 at 9:29
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    \$\begingroup\$ Yes that can happen with intermodulation and pulse supply coils with sidebands in the audio range. Where are your design details? [[Edited: RMc]] \$\endgroup\$ Commented Oct 11, 2020 at 9:43
  • \$\begingroup\$ Whining noise and a high voltage between cathode and common anode sound a lot like PWM to me. \$\endgroup\$
    – Oskar Skog
    Commented Oct 11, 2020 at 11:42

1 Answer 1


IIRC, analog write on Arduino uses PWM (pulse width modulation).

The whining noise you hear from the power supply might be because of the PWM.

The voltage you measured between common positive and red negative of the LED strip (I assume that is what you measured) also sounds reasonable. If you measure DC voltage with a multimeter, it will measure the average voltage. If you switch the meter to AC voltage you should see some voltage. The DC voltage is 12 V only when the color component is fully on and 0 V only when it's fully off.

If nothing else seems out of the ordinary then it's normal.


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