Working with multiplexers for constant voltage output I'm working on creating a circuit where I'm trying to have the ability to switch multiple strands of LED rope on and off at a time using an Arduino and a multiplexer. 

With my current configuration, I have the a circuit and a sketch that will cycle through the various LED rope strands, turning them on and off. 

What I'm not sure how to do is modify my sketch / circuit so that I can turn ALL of the rope strands on and off, as well as individually. 

Below is my current Arduino sketch:

//Mux control pins
int s0 = 8;
int s1 = 9;
int s2 = 10;
int s3 = 11;

//Mux in "SIG" pin
int SIG_pin = 3;

int testValue = 255;


void setup(){
  pinMode(s0, OUTPUT); 
  pinMode(s1, OUTPUT); 
  pinMode(s2, OUTPUT); 
  pinMode(s3, OUTPUT); 


  pinMode(SIG_pin, OUTPUT);

  digitalWrite(s0, LOW);
  digitalWrite(s1, LOW);
  digitalWrite(s2, LOW);
  digitalWrite(s3, LOW);

}


void loop(){

  //Loop through and read all 16 values
  //Reports back Value at channel 6 is: 346
  for(int i = 0; i &lt; 9 ; i ++){
    delay(1000);
    writeMux(i);    
  }
}


int writeMux(int channel){
  int controlPin[] = {s0, s1, s2, s3};

  int muxChannel[10][4]={
    {0,0,0,0}, //channel 0
    {1,0,0,0}, //channel 1
    {0,1,0,0}, //channel 2
    {1,1,0,0}, //channel 3
    {0,0,1,0}, //channel 4
    {1,0,1,0}, //channel 5
    {0,1,1,0}, //channel 6
    {1,1,1,0}, //channel 7
    {0,0,0,1}, //channel 8
    {1,0,0,1}, //channel 9
    {0,1,0,1}, //channel 10
    {1,1,0,1}, //channel 11
    {0,0,1,1}, //channel 12
    {1,0,1,1}, //channel 13
    {0,1,1,1}, //channel 14
    {1,1,1,1}  //channel 15
  };

  //loop through the 4 sig
  for(int i = 0; i &lt; 4; i ++){
    digitalWrite(controlPin[i], muxChannel[channel][i]);
  }

  //read the value at the SIG pin
  analogWrite(testValue, SIG_pin);  


  //return the value
  return 0;
}


I'm using two multiplexers to control multiple rope strands. Here's roughly what that looks like:



I'm still a bit new to electronics prototyping (coming from software development); so I'm not sure if what I want to do is possible with a multiplexer 

Happy to start offer a bounty to a helpful answer. 

Thank you
Even I am new to this and I also find it a bit challenging with the available setup and desired output. Though it seems tough, I want you to just try out this code (it is a little modification to the one posted by you) and check whether it matches the expected result.

    //Mux control pins
#define s0 8;
#define s1 9;
#define s2 10;
#define s3 11;

//Mux in "SIG" pin
#define SIG_pin 3;

#define testValue 255;  //maximum value for analogWrite() function

void setup()
{
  pinMode(s0, OUTPUT); 
  pinMode(s1, OUTPUT); 
  pinMode(s2, OUTPUT); 
  pinMode(s3, OUTPUT); 

  pinMode(SIG_pin, OUTPUT);

  digitalWrite(s0, LOW);
  digitalWrite(s1, LOW);
  digitalWrite(s2, LOW);
  digitalWrite(s3, LOW);
}

void loop()
{
  //Loop through and read all 16 values
  for(int i = 0; i &lt; 16 ; i ++)
  {
    delay(1000);
    writeMux(i);
  }
}


int writeMux(int channel)
{
  int controlPin[] = {s0, s1, s2, s3};

  int muxChannel[16][4]=
  {
    {0,0,0,0}, //channel 0
    {1,0,0,0}, //channel 1
    {0,1,0,0}, //channel 2
    {1,1,0,0}, //channel 3
    {0,0,1,0}, //channel 4
    {1,0,1,0}, //channel 5
    {0,1,1,0}, //channel 6
    {1,1,1,0}, //channel 7
    {0,0,0,1}, //channel 8
    {1,0,0,1}, //channel 9
    {0,1,0,1}, //channel 10
    {1,1,0,1}, //channel 11
    {0,0,1,1}, //channel 12
    {1,0,1,1}, //channel 13
    {0,1,1,1}, //channel 14
    {1,1,1,1}  //channel 15
  };

  //loop through the 4 sig
  for(int i = 0; i &lt; 4; i ++)
  {
    digitalWrite(controlPin[i], muxChannel[channel][i]);
  }

  //read the value at the SIG pin
  for(int i_testValue = 0; i_testValue &lt; testValue; i_testValue++)
  {
    analogWrite(i_testValue, SIG_pin);      //incresing intensity slowly with delay of 100ms
    delay(100);
  }


  //return the value
  return 0;
}