03-05-2011, 12:33 PM
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The circuit as shown in the figureemploys 14 bi-colour (red andgreen) LEDs having three terminalseach. Different dancing colour patternsare produced using this circuit sinceeach LED can produce three differentcolours. The middle terminal (pin 2) of theLEDs is the common cathode pin which isgrounded. When a positive voltage is appliedto pin 1, it emits red light. Similarly,when positive voltage is applied to pin
It emits green light. And when positive voltageis simultaneously applied to its pins 1and 3, it emits amber light. The circuit canbe used for decorative lights.IC1 (555) is used in astable mode togenerate clock signal for IC2 and IC3(CD4518) which are dual BCD counters.Both counters of each of these ICs havebeen cascaded to obtain 8 outputs fromeach. The outputs from IC2 and IC3 areconnected to IC4 through IC7 which areBCD to 7-segment latch/decodor/driverICs. Thus we obtain a total of 14 segmentoutputs from each of the IC pairsconsisting of IC4 plus IC5 and IC6 plusIC7. While outputs from former pairare connected to pin No. 1 of all the14 bi-colour LEDs via current limitingresistors, the ouputs of the latter pairare similarly connected to pin No.3 ofall the bi-colour LEDs to get a magicaldancing lights effect.
