LED Strip Lighting Project- a few questions.

Hey all!
So I am working on a project for school that has LED strip lighting controlled by Arduino. I am using two tutorials- http://www.instructables.com/id/Arduino-Controlled-LED-Strip-Holiday-Lighting/ and https://learn.adafruit.com/rgb-led-strips/example-code to do it. I also have a Maker Shield for my Uno. I also have connector cable wire, transistors, and LED strips.
The first tutorial calls for only 2 LED strips, but I need to use 3. First off, is it even possible to connect 3 strips to what I have, and if so, how and where exactly would I connect it? The tutorials were a bit vague in describing where to solder. If this isn’t possible, what would you recommend I use to make this happen?

And lastly, I want the lights to switch from red to blue (and blue to red) at random intervals. I modified some code from one of the tutorials, and I need to figure out how to make it switch randomly. This is what I have so far:

// Color Changer for 3 Analog LED Strips
  
    // 3 LED strips with R, G, B LEDS on each, so there are 9 channels to control via FET transistors
    // use the 9 PWM digital I/O pins for the FET gate pins
    #define R1 3
    #define G1 5
    #define B1 6
    #define R2 9
    #define G2 10
    #define B2 11
    #define R3 13
    #define G3 14
    #define B3 15
    
    #define FADESPEED 7 // make this higher to slow down
    
    void setup() {
      // set all the LEDs to off
      analogWrite(R1, 0);
      analogWrite(G1, 0);
      analogWrite(B1, 0);
      analogWrite(R2, 0);
      analogWrite(G2, 0);
      analogWrite(B2, 0);
      analogWrite(R3, 0);
      analogWrite(G3, 0);
      analogWrite(B3, 0);

    }
    
    void loop() {
      int i;
    
      // fade strip 1 red up and strip 2 red up
      for (i = 0; i < 256; i++) {
        analogWrite(R1, i);
        analogWrite(R2, i);
        delay(FADESPEED);
      }
      
      // fade strip 1 red down and strip 2 red down
      for (i = 0; i < 256; i++) {
        analogWrite(R1, 255-i);
        analogWrite(R2, 255-i);
        delay(FADESPEED);
      }
      
      // fade strip 1 blue up and strip 2 blue up
      for (i = 0; i < 256; i++) {
        analogWrite(B1, i);
        analogWrite(B2, i);
        delay(FADESPEED);
      }
      
      // fade strip 1 blue down and strip 2 blue down
      for (i = 0; i < 256; i++) {
        analogWrite(B1, 255-i);
        analogWrite(B2, 255-i);
        delay(FADESPEED);
      }
      
          
  }

Any pointers or corrections would be much appreciated. This is my first time using Arduino. Thank you!

Just skimming through the Instructables page it says:

(6) N-Channel Power MOSFET transistors from Adafruit - you need one per color. Since I had two strips with R, G, B on each, I needed 6 of them. There are other ways to do this, but the nice thing about the MOSFETs is there are no other components needed.

I assume you'd need 3 more MOSFETS wired the same way as the others.

For randomness you can use the [u]random() function[/u].

For example, you can make FADESPEED into a regular integer variable (instead of using #define) and you could change it to a new random number between 5 and 10 every time you start the loop.

Which Arduino are you using.
PWM pin 13, 14, 15 ?

Uno.
I'm guessing it doesn't exist, then? :cold_sweat:
I'm a newb. I need to know where to stick the third strip...

Only six PWM pins on an Uno.

Leo..

I found a spare Arduino Mega in one of my classrooms- how much of a difference will this make? Can I do 3 with this one?

AFAIK, a Mega has 15 PWM pins.
So you can drive five RGB strips with that one.
Leo..

Alrighty, next questions- and I apologize for asking anything potentially obvious- where exactly am I soldering the transistors and strip connectors to? This photo (not mine) kinda shows where you would attach things to the MakerShield, but the tutorial doesn't tell you how- just photos. Then, this photo has a better view- so would I just line up the wires with the transistors and solder them?
Again, sorry for asking so much, I just want this to work...