A STABLE RGB LEDs BASED LIGHT SOURCE WITH CONTROL MECHANISM UTILIZING LOW COST MICROCONTROLLER

摘要

This paper focuses on the design and implementation of colour control mechanism for red, green and blue (RGB) light emitting diodes (LEDs) light source. The additive mixing by the primary LED requires a control mechanism since a produced colour are subjected to variation such as that ambient temperature variation and the self-heating of the LEDs. The colour point will vary because the individual LED's output radiant intensity degradation is not the same. In this design, a low cost microcontroller was employed as a central unit to store initial set point of the colour mixing and control each LED when the difference between measured colour point and initial set point exceeded a set tolerance. The control method relied on the difference of the radiant intensity measured by a simple optical sensor and predicted PWM for LEDs. The developed colour control mechanism effectively maintained the mixed colour point when it was subjected to an accelerated ambient temperature test. The system was capable to detect the changes of the LED radiant flux and forward voltage and maintain colour point within a minimum accuracy of at least 20 least significant bit (LSB).