COLOR_SHIFTING_LED_DISPLAY

Published:2009/6/18 4:14:00 Author:May | From:SeekIC

This circuit is used to make a tricolor LED gradually change color from yellow to red to yellow to green, and then back to yellow, where the cyclerepeats. It is very simple to make, and the theory of operation is also simple. Both of the timers in the556 dual oscillator/timer are configured for astable operation with a 50% duty cycle. 0ne timer is set uEDt to oscillate much faster than the other. The timing capacitor voltage of each is sent to two comparators, which apply a voltage across the tri-color LED whose polarity depends on which capacitor voltageis higher. The rapidly changing capacitor's voltage causes the red and green elements of the LED tobe altemately lit, thus giving the illusion of yeilow light. As the slowly rising and faLing voltage from the slower trimming capacitor changes in average value, it shifts the duty cycle to favor one color or the other. That gives the transition between colors a smooth appearance.



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