Arduino Controlled LED Light Strip

The following is a schematic for driving an LED light strip with 4 contacts (12V, R, G and B) using an Arduino. A power source is used to power the Arduino via a step-down module to as well as the LED light strip via its 12V pin. The three R, G, B LED pins are controlled via three transistors having the emitter connected to the common ground (common with the step down and the power supply). The transistor act as latches, in this case, opening the feed of current from the R, G and B contacts to the ground. In doing so, each component red, green and blue is lit up and mix to form a desired color. In order to achieve the full spectrum of colors, the Arduino GPIO pins will output an analog signal (via the analogWrite function) in order to control the amount of current flowing from the collector connected to the component pins and to the ground. If the GPIO pins were to output a digital signal level, then only a few colors could be achieved since only toggling the R, G and B components on and off would be possible.

                                            12V
      +-------------------------+------------->
      |                         |
   +--+--+                +-----+-----+
   | 12V |                | 12V -> 5V |
   +--+--+                +-----+-----+
      |                         |
      |                         |            R
      |          +---------+ 5V |   +--------->
      |      GND |         |----+   |
      +----------+         |        /
                 |    GPIO +------|+
                 |         |        \ e
                 |         |        v
                 |         |        |
                 |         |       GND
                 | Arduino |                 G
                 |         |        +--------->
                 |         |        |
                 |         |        /    
                 |    GPIO +------|+         
                 |         |        \ e
                 |         |        v
                 |         |        |
                 |         |       GND
                 |         |                 B
                 |         |        +--------->
                 |         |        |
                 |         |        /
                 |    GPIO +------|+          
                 |         |        \ e
                 |         |        v
                 |         |        |
                 +---------+       GND

Since the gate should be opened varying with the analog signal of the GPIO pins, the transistor type used is an NPN trnasitor. The actual model of the transistor depends greatly on how many LEDs are contained on an LED strip. Most projects involving this type of LED strip control use power-transitors that are capable of driving a large amount of LEDs however, even a general purpose 2N3904 transistor is capable of switching up to from the collector to the emitter and carry between to of power which may be sufficient for a smaller LED light strip depending on its power consumption.