Versatile Multi-Color LED Operation
A light-emitting diode (LED) capable of emitting different colors when forward or reverse biased is known as a multi-color LED. Essentially, it integrates multiple light-emitting diodes of various colors within a single electronic device. The Everlight Type 339-1 VRKG-BBW exemplifies this innovation, housing four LEDs in one casing: one red, one green, and two blue LEDs. By adjusting the brightness levels of these LEDs, it’s possible to produce all visible colors and even white light. The circuit outlined here enables these LEDs to illuminate in any color sequence desired.
Oscillator Circuit for Multi-Color Illumination
The circuit comprises an integrator followed by a Schmitt trigger, creating an oscillator that generates a triangular voltage signal with an amplitude of approximately 1.5 Vpp at pin 1. This triangular signal is then directed to one of the LEDs through T1 and the current-limiting resistor R5, allowing for the dynamic illumination of the multi-color LED in a wide array of colors.
Individual Circuits for Each LED Color
For this setup, three distinct circuits need to be constructed: one for the red LED, another for the green LED, and a third for the two blue LEDs. Each circuit, however, should incorporate a different value for capacitor C1, such as 470 nF, 330 nF, and 220 nF. Additionally, even though the blue LEDs are connected to the same circuit, each one should have its own dedicated series resistor.
Adjusting Triangular Signal Level
The direct voltage level of the triangular signal can be adjusted using P1. Begin with the wiper at ground, then slowly adjust the control until the LED just starts to illuminate. The optimal setting is achieved when the LED remains lit for two-thirds of the time and is off for the remaining one-third.
Careful Adjustment and Current Limitation
It’s crucial not to over-adjust P1. Ensure that the current passing through the red and green LEDs does not exceed 30 mA. While the blue LEDs can draw up to 40 mA each. The sensitivity of the blue LEDs demands caution. The series resistors are kept at a low value due to this sensitivity. Maintaining an average current draw of approximately 70 mA for the entire circuit.