 
 A Vernier Photogate should also be connnected to the second BTD 1 connector.
 The sketch monitors this photogate and Controls a stepper motor (unipolar or 
-bipolar) via a Vernier Digital Control Unit (DCU) connected to the second BTD 
+bipolar) via a Vernier Digital Control Unit (DCU) connected to the BTD 2 
 connector.
 
 This sketch will continuously check the photogate and start the stepper

int Direction =0;//direction 0 =CW
int x;
int StepValue;
//the lines below are so that you can quickly change this code if you want to
//use the DCU in the BTD1 connector for some reason.
int DCUinBTD2=1;// change this to 0 if you want to use the DCU on BTD 1
const int Pin1 = 2 +DCUinBTD2*4;
const int Pin2 = 3 +DCUinBTD2*4;
const int Pin3 = 4 +DCUinBTD2*4;
const int Pin4 = 5 +DCUinBTD2*4;
int photogate =2; //This is the input for a photogate on the BTD 1 connector
int LEDpin =13;/// line for LED to turn on when photogate is blocked
int output; //number sent to DCU

    } ;//end of for
};// end of Step
 
void DCU (int output) 
/* This segment is used for all DCU applications.
Not all only cases 0 - 3 will be used in this sketch. */
{
  switch (output) 
  {
