plotter pen up/down control

/* a sketch to use a an arduino or derivative and a L293D as a stepper motor controller
with an additional homing button (pen up/pen down for example)
Uses optionally John Zandbergen's enhancement to the stepper library to do half-stepping
http://code.google.com/p/arduino/issues/detail?id=139
the arduino responds to standard STEP, DIR and ENABLE signals
we have only an upper limit stop sensor, the lower limit is done in software
*/

#define IN_DIR_PIN 12
#define IN_STEP_PIN 13
#define IN_ENABLE_PIN 8
#define STEPPER_ENABLE_PIN 7
#define STEPPER_PIN_A1 11 
#define STEPPER_PIN_A2 10
#define STEPPER_PIN_B1 6
#define STEPPER_PIN_B2 5
#define IN_Z_LIM_PROX_PIN 3
#define OUT_Z_LIM_PROX_PIN 14
#define OUT_Z_LIM_DIST_PIN 1
#define IN_HOME_SWITCH_PIN 4
#define UP 1
#define DOWN -1
#define ZLENGTH 54
#define USE_HALF_STEP 0
#define ENABLED 1
#define DISABLED 0

// change this to your motor's number of steps per turn
#define STEPS 48
 
#include <HalfStepper.h>

int zButtonState = 0 ;  // current z button state
int zLastButtonState = 0 ; // previous state of the z button
int zButtonPushCounter = 1 ; // push counter for the z button
int zProxLimState = LOW ; // z prox limit sensor state  
int zpos = 0 ; // keeps the current z position. 0 is all the way up.
int ztarget = 0 ; // target position
int direction = 0 ;
int enableState = DISABLED ;
int doStep = 0 ;

// create an instance of the stepper class, specifying
// the number of steps of the motor and the pins it's
// attached to
Stepper stepper(STEPS, STEPPER_PIN_A1, STEPPER_PIN_A2, STEPPER_PIN_B1, STEPPER_PIN_B2, USE_HALF_STEP);

void setup()
{
 pinMode(IN_DIR_PIN, INPUT) ;  
 pinMode(IN_STEP_PIN, INPUT) ;
 pinMode(IN_ENABLE_PIN, INPUT) ;
 pinMode(IN_HOME_SWITCH_PIN, INPUT);
 pinMode(IN_Z_LIM_PROX_PIN, INPUT);
 pinMode(OUT_Z_LIM_PROX_PIN, OUTPUT);
 pinMode(STEPPER_ENABLE_PIN, OUTPUT) ;   
 pinMode(STEPPER_PIN_A1, OUTPUT) ;
 pinMode(STEPPER_PIN_A2, OUTPUT) ;
 pinMode(STEPPER_PIN_B1, OUTPUT) ; 
 pinMode(STEPPER_PIN_B2, OUTPUT) ;  
    
  // set the speed of the motor to  RPMs. Use something adapted to your particular stepper
  stepper.setSpeed(200);
}

void readButton() {
  zButtonState = digitalRead(IN_HOME_SWITCH_PIN);  
}

void homePen() {
   if (zButtonState != zLastButtonState) {
   if (zButtonState == LOW) {
    zButtonPushCounter++ ;
  if (zButtonPushCounter % 2 == 0) {
      homeUp();
  } else {
      homeDown();
      } 
     }
    } 
 zLastButtonState = zButtonState;
}

void homeUp() {
    digitalWrite(STEPPER_ENABLE_PIN, HIGH);         // enable the L293D output
  while (true) {
  zProxLimState = digitalRead(IN_Z_LIM_PROX_PIN) ;  // check if we have activated the upper limit sensor
  
  if (zProxLimState == HIGH) {
    zpos = 0 ;                                      // we are at the top. Let this position be 0
    digitalWrite(OUT_Z_LIM_PROX_PIN, HIGH);         // Notify the hierarchy we reached the limit
    break ;     // get outta here
   }
    stepper.step(UP) ;                  
  }
  digitalWrite(STEPPER_ENABLE_PIN, LOW); // disable the L293D output
}

void homeDown() {
  digitalWrite(STEPPER_ENABLE_PIN, HIGH); // enable the L293D output
  ztarget = ZLENGTH - zpos ;
  for(int i = 0; i <= ztarget; i++) {
     stepper.step(DOWN) ;
     zpos = zpos + 1 ; // update position counter
     if (zpos > 0) {
             digitalWrite(OUT_Z_LIM_PROX_PIN, LOW);  // 
     }
     if (zpos == ZLENGTH) {
            digitalWrite(OUT_Z_LIM_DIST_PIN, HIGH) ;         // Advertise we have reached the lower limit
     } else if (zpos < 100) {
            digitalWrite(OUT_Z_LIM_DIST_PIN, LOW) ;          // all OK
     }
  }
 digitalWrite(STEPPER_ENABLE_PIN, LOW); // disable the l293D output
}

void listenCommands(){
direction = digitalRead(IN_DIR_PIN);
enableState = digitalRead(IN_ENABLE_PIN);
doStep = digitalRead(IN_STEP_PIN);
}

void doStuff(){
  if (enableState == ENABLED) {
         if (direction == 1) {
              homeUp();
         }
         if (direction == 0) {
               homeDown();
         }
  }
   
  if (enableState == DISABLED) {
       digitalWrite(STEPPER_ENABLE_PIN, LOW); // disable the L293D output
  }
}

void loop()
{
  readButton() ;      // check manual button
  homePen() ;         // do manual pen up / pen down
  listenCommands();   // check for signals
  doStuff();          // take the actual actions
}