Instead of using two different color LEDs for the indicator lamp, we can use a single Bi-color LED to indicate two different colors.Similarly, if we give a positive signal to both the terminals of LED, a color depending upon the combination of both colors will flash. This causes the red LED to glow while the green LED remains off. For example, if we are using a green and red color bi-polar LED then a positive signal applied at the red terminal and a negative signal applied at the green terminal ensures that the red LED is forward biased. ![]() The functioning of the LED depends upon the positive signal given to one of the terminals. The second LED terminal is directly connected to the output pin of the 555 timers and it turns on when the output of the 555 timers is High. I got so antsy to want to control more than one RGB LED, that I went to radio shack and saw they had a 'full color' led. I am playing with the make arduino starter kit I got in the last week like crazy. Forum 2005-2010 (read only) Hardware Interfacing. So driving one of these means running a current from the particular anode (positive) pin for the desired segment to the common cathode pin. One of the terminals of the LED is receiving output through a PNP transistor, which turns on when the output of the 555 timers is Low. RGB LED Common Cathode versus Common Anode. Common cathode means that the cathodes of all of the LEDs are common and connected to a single pin. Output pin 3 is connected to the two terminals of the LED. We are using 555 timer IC in the astable mode for this project. Connect LED as shown in the circuit diagram.Connect the emitter of the transistor to VCC.Add a 33K Ω resistor between Pin 3 and Pin 6.Connect a 4.7K Ω resistor between the Base of transistor & VCC.Use a 10K Ω resistor to connect Pin 3 to the base of the transistor.Use a jumper wire to connect Pin 6 & Pin 2 together.Place the 555 Timer IC on a breadboard and connect Pin 4 & Pin 8 To VCC.
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