Multi-color-led: A LED that emits one color when forward biased and another color when reverse biased is called a multi-color-led or we can say that a multi-color-led is an electronic device incorporating light-emitting diodes of more than one color. It had to come: with an LED that can produce all visible colors. It is the Everlight Type 339-1 VRKG-BBW. In fact, it consists of four LEDs in one case: one red, one green, and two blue. When these LEDs are driven into varying brightnesses, all visible colors and white can be produced. The circuit described makes the LEDs light in all colors in any given order.
The circuit consists of an integrator followed by a Schmitt trigger. Together these form an oscillator that produces a triangular voltage with an amplitude of about 1.5 Vpp at its pin 1. This signal is applied to one of the LEDs via T1 and current limiting resistor R5.
Three of these circuits should be built: one for the red. and one for the green. and one for the two blue LEDs. Each circuit should. however, have a different value C1. say, 470 nF, 330 nF, and 220 nF Each of the blue LEDs. although connected to the same circuit. should have its own series resistor.
The direct voltage level of the triangular signal may be shifted with P1. Start with the wiper at the earth, and then turn the control very slowly till the LED just begins to light. The best setting is when the LED lights for two-thirds of the time and is off for one-third.
The value of the series resistors is low, because of the sensitivity, especially of the blue LEDs. is low.
Do not turn P1 so far, but take care that the current through the red and green LEDs remains below 30 mA: the blue ones can draw up to 40 mA. The average current drawn by the circuit is then about 70 mA.