This circuit shows how an Arduino controls an RGB LED using three output pins. An RGB LED contains three internal LEDs—Red, Green, and Blue—combined in one package. In this diagram, it is a common cathode type, meaning all the negative terminals are connected together and tied to ground.
Each color pin (R, G, B) is connected to a separate Arduino digital/PWM pin through a 220Ω resistor (R1, R2, R3). These resistors limit current and protect both the LED and the Arduino.
When the Arduino sends a HIGH signal to any pin, current flows through the resistor and the corresponding LED color turns ON. By using PWM (pins marked with ~), the brightness of each color can be adjusted. By mixing different brightness levels of Red, Green, and Blue, a wide range of colors can be produced.
For example:
Red + Green = Yellow
Red + Blue = Magenta
Green + Blue = Cyan
All three = White
This is the basic principle behind color mixing in displays and lighting systems.

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Controlling DC motor speed using voltage directly is inefficient, so this circuit uses Pulse Width Modulation (PWM) to do it more effectively. A 555 timer generates a square wave where the ON time and OFF time can be adjusted using the variable resistor (VR1). When the pulse is narrow, the motor receives power for a shorter time, resulting in lower average voltage and slower speed. When the pulse is wide, the motor gets power for longer duration, increasing the average voltage and making it spin faster. The diodes around the potentiometer help control the charge and discharge paths separately, allowing smooth duty cycle adjustment. The output from the 555 timer drives a power transistor (2N3055), which acts like a switch to supply current to the motor. A diode across the motor protects the circuit from voltage spikes generated when the motor turns off. This method provides efficient speed control with minimal power loss.
#ElectronicsEducation #ElectronicsRD #PWM #DCMotor #555Timer
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