Backlighting And RGB Bling bling. QMK-Compatible LED backlighting This is one LED per switch. The structure is: . |- LED --- Resistor -| | | N-Channel 5V ---|- LED --- Resistor -|----- MOSFET ----- GND | | | |- LED --- Resistor -| PWM PIN Use a N-channel MOSFET. A PWM pin can only deliver around 20mA absolute maximum. Drawing tons of LEDs from a single PWM pin will easily fry your microchip. Place a resistor between the PWM pin and MOSFET gate. All LED-Resistor pairs are placed in parallel. All LEDs can be run under a few or single resistor, but this leads to brightness inconsistencies among the LEDs. The current from the LED-Resistor pairs feed into the drain of the MOSFET. PWM feeds into the gate of the MOSFET with a 100~1k or so resistor, usually. Source of the MOSFET goes to ground. Each LED resistor should be planned to let around 1-5mA through the LEDs each. 20mA will hurt your eyes. Choosing the correct MOSFET Power Dissipation Make sure the current flowing through times the voltage drop doesn't lead to a power dissipation that doesn't fry the MOSFET. Maximum voltage and current Check for Drain-Source voltage/current max ratings. Size Do not pick a MOSFET which will not fit on your PCB. RGB Underglow WS2812B is the standard used for underglow. Draws 45-50mA per package maximum. However, AliExpress GH60 PCBs have 16 WS2812B. Current can be limited via QMK. Can be daisy-chained together. One LED passes data onto the next, and so on. Can be purchased in individual WS2812B or by strips. Use individual for assembled PCBs. Wired in the following way: VDD to 5V VSS to GND DIN to previous LED DOUT, or AVR pin if first LED DOUT to next LED DIN, or unconnected if last LED Placing a 500 ohm resistor between AVR pin and first LED is highly recommended Various other RGB choices WS2812 (without B) - Unsimplified version of WS2812B with 6 pins WS2811 - The controller within WS2812B. Can be used as standalone controller with other RGBs. Controller-less RGBs - Use with separate PWM LED controllers. WS2812C - Low current variant SK6812 - An alternative that also works with QMK Indicator LEDs Simplest. MCU PIN --- LED --- Resistor --- GND (Source setup - Toggle pin high to turn on) or 5V --- LED --- Resistor --- MCU PIN (Sink setup - Toggle pin high to turn off) LED and resistor can be swapped.