RGB Led Color Mixer

This simple RGB led color mixer uses NO microcontrollers ( Arduino - Pic etc ). It controls the brightness of each color channel by varying the duty cycle (On time vs OFF time) by a technique named PWM or pulse width modulation. This results in a very low power dissipation, as leds are either fully on or off. The circuit manages the three channels with only 1 common integrated circuit and 2 transistors.

Main components:

IC1: TL084 (quad FET input op-amp)

Q1: BC558 (general purpose PNP transistor)

Q2: BC548 (general purpose NPN transistor)

D1-D6 1N4148 diodes

VR1-VR3 10Kohm Linear potentiometers

LED: RGB common cathode led

This in turn determines the time each led will be ON during each sawtooth oscillator cycle, making it appear to be brighter or darker to the eye.

For this demo I am driving the LEDs directly from the OP-amp, but you can drive any power leds, by adding a power mosfet or transistor.