user24018: I am driving two stepper motor using serial data from Raspberry Pi to Arduino. Motors work fine when i am passing serial data but once i stop sending serial data, it doesn't accept serial data again unless I burn the program again in arduino. Here is code for that:
 #include <Driver.h>

//////////////////////////////////////////////////////////////////////////////////////////
/*
   Hardware pins defined in this section as connected from arduino to Pan DRV8834
   controller and tilt DRV8834 controller.M0 and M1 pins are common for both controllers
   ,hence declared only once(This is done to save number of pins, connecting it to
   additional pins , provide no special advantage since both both motors should be set
   to same level of microstepping).SLP pin is not currently used.

*/
//////////////////////////////////////////////////////////////////////////////////////////

#define PAN_DIRECTION_PIN 8
#define TILT_DIRECTION_PIN 7

#define PAN_STEP_PIN 10
#define TILT_STEP_PIN 9

#define M0 6
#define M1 5

#define MOTOR_SPEED 200

#define SLP 0
///////////////////////////////////////////////////////////////////////////////////////////

#define BAUD_RATE 230400      //Baud Rate for serial communication

///////////////////////////////////////////////////////////////////////////////////////////

/*
   field data for receiving buffer on arduino side , important for serial communication
*/
#define NUMBER_OF_FIELDS 2 // how many comma separated fields we expect
int fieldIndex = 0;           // the current field being received
int values[NUMBER_OF_FIELDS];  // array holding angles for both motors

const char startChar = '<'; //beginning character of a valid command
const char endchar   = '>'; //this will be ending character to ensure a valid command has ended
boolean storeString = false; //This will be our flag to put the data in our buffer

#define zeroCharacter 'z'

bool zeroCommand = false;

#define DATABUFFERSIZE 50
char dataBuffer[DATABUFFERSIZE + 1]; //Add 1 for NULL terminator
int dataBufferIndex = 0;


int procBufCounter;         //iterate through whole string to obtain the commands


float panAngle, tiltAngle;

int sign = 1;



    Driver stepper_pan(M0, M1, PAN_STEP_PIN, SLP, PAN_DIRECTION_PIN);
    Driver stepper_tilt(M0, M1, TILT_STEP_PIN, SLP, TILT_DIRECTION_PIN);


    void processCommand(char *buffer) {

        procBufCounter = 0;
        bool startprocessing = false;
        bool endprocessing = false;

        values[0] = 0;
        values[1] = 0;

        while ((procBufCounter < DATABUFFERSIZE) && (!endprocessing)) {

            char ch = buffer[procBufCounter];           //read the character while simulatneously increasing the buffer cursor



            if (ch == '<') {
                startprocessing = true;
            }
            else if (ch == '>') {
                values[fieldIndex] = values[fieldIndex] * sign ;
                fieldIndex = 0;
                endprocessing = true;
            }

            if (startprocessing)
            {
                if (ch == ',') {
                    values[fieldIndex] = values[fieldIndex] * sign ; // set value to the accumulated value
                    sign = 1;
                    fieldIndex++;
                }
                else if ('0' <= ch && ch <= '9' ) {
                    values[fieldIndex] = (values[fieldIndex] * 10) + (ch - '0');
                }
                else if (ch == '-') {
                    sign = -1;
                }
                else if(ch == 'z'){
                  zeroCommand = true;
                }
            }
            procBufCounter++;
        }
        panAngle = ((float)(values[0]))/100;
        tiltAngle = ((float)(values[1]))/100;


       bool panMoved = true, tiltMoved = true;
        stepper_pan.moveTo(panAngle);
        stepper_tilt.moveTo(tiltAngle);
      while (panMoved || tiltMoved) {
        panMoved = stepper_pan.run();
        tiltMoved = stepper_tilt.run();
      }

      if(zeroCommand){
        stepper_pan.reset_positions();
        stepper_tilt.reset_positions();
        zeroCommand = false;
      }


    }

    //////////////////////////////////////////////////////////////////////////////////////

    void setup() {
      stepper_pan.setStepMode(STEP_THIRTYTWO);
      stepper_pan.setSpeed(MOTOR_SPEED);
      stepper_tilt.setStepMode(STEP_THIRTYTWO);
      stepper_tilt.setSpeed(MOTOR_SPEED);
      Serial.begin (BAUD_RATE);
      Serial.flush();
    }

    void loop() {
      if (processString) {
        processCommand(dataBuffer);
        processString = false;
    //     dataBuffer = "";

      }
    }

    void serialEvent() {
      static int dataBufferIndex = 0;
      while (Serial.available() > 0) {
        char incomingbyte = Serial.read();
        if (incomingbyte == startChar) {
          dataBufferIndex = 0;  //Initialize our dataBufferIndex variable
          storeString = true;
        }
        if (storeString) {
          //Let's check our index here, and abort if we're outside our buffer size
          //We use our define here so our buffer size can be easily modified
          if (dataBufferIndex == DATABUFFERSIZE) {
            //Oops, our index is pointing to an array element outside our buffer.
            dataBufferIndex = 0;
            break;
          }
          if (incomingbyte == endchar) {
            dataBuffer[dataBufferIndex] = endchar; //null terminate the C string
            dataBuffer[dataBufferIndex + 1] = '\0';
            //Our data string is complete.  return true
            storeString = false;
            processString = true;
            dataBufferIndex = 0;
          }
          else {
            dataBuffer[dataBufferIndex++] = incomingbyte;
            dataBuffer[dataBufferIndex] = 0; //null terminate the C string
          }
        }

      }

    }


user24018: I finally figured it out. It is due to reset whenever I open a port for serial communication. Attaching a 10uF capacitor between ground and reset fixed everything.

24018: <p>I am driving two stepper motor using serial data from Raspberry Pi to Arduino. Motors work fine when i am passing serial data but once i stop sending serial data, it doesn't accept serial data again unless I burn the program again in arduino. Here is code for that:</p>

<pre><code> #include &lt;Driver.h&gt;

//////////////////////////////////////////////////////////////////////////////////////////
/*
   Hardware pins defined in this section as connected from arduino to Pan DRV8834
   controller and tilt DRV8834 controller.M0 and M1 pins are common for both controllers
   ,hence declared only once(This is done to save number of pins, connecting it to
   additional pins , provide no special advantage since both both motors should be set
   to same level of microstepping).SLP pin is not currently used.

*/
//////////////////////////////////////////////////////////////////////////////////////////

#define PAN_DIRECTION_PIN 8
#define TILT_DIRECTION_PIN 7

#define PAN_STEP_PIN 10
#define TILT_STEP_PIN 9

#define M0 6
#define M1 5

#define MOTOR_SPEED 200

#define SLP 0
///////////////////////////////////////////////////////////////////////////////////////////

#define BAUD_RATE 230400      //Baud Rate for serial communication

///////////////////////////////////////////////////////////////////////////////////////////

/*
   field data for receiving buffer on arduino side , important for serial communication
*/
#define NUMBER_OF_FIELDS 2 // how many comma separated fields we expect
int fieldIndex = 0;           // the current field being received
int values[NUMBER_OF_FIELDS];  // array holding angles for both motors

const char startChar = '&lt;'; //beginning character of a valid command
const char endchar   = '&gt;'; //this will be ending character to ensure a valid command has ended
boolean storeString = false; //This will be our flag to put the data in our buffer

#define zeroCharacter 'z'

bool zeroCommand = false;

#define DATABUFFERSIZE 50
char dataBuffer[DATABUFFERSIZE + 1]; //Add 1 for NULL terminator
int dataBufferIndex = 0;


int procBufCounter;         //iterate through whole string to obtain the commands


float panAngle, tiltAngle;

int sign = 1;



    Driver stepper_pan(M0, M1, PAN_STEP_PIN, SLP, PAN_DIRECTION_PIN);
    Driver stepper_tilt(M0, M1, TILT_STEP_PIN, SLP, TILT_DIRECTION_PIN);


    void processCommand(char *buffer) {

        procBufCounter = 0;
        bool startprocessing = false;
        bool endprocessing = false;

        values[0] = 0;
        values[1] = 0;

        while ((procBufCounter &lt; DATABUFFERSIZE) &amp;&amp; (!endprocessing)) {

            char ch = buffer[procBufCounter];           //read the character while simulatneously increasing the buffer cursor



            if (ch == '&lt;') {
                startprocessing = true;
            }
            else if (ch == '&gt;') {
                values[fieldIndex] = values[fieldIndex] * sign ;
                fieldIndex = 0;
                endprocessing = true;
            }

            if (startprocessing)
            {
                if (ch == ',') {
                    values[fieldIndex] = values[fieldIndex] * sign ; // set value to the accumulated value
                    sign = 1;
                    fieldIndex++;
                }
                else if ('0' &lt;= ch &amp;&amp; ch &lt;= '9' ) {
                    values[fieldIndex] = (values[fieldIndex] * 10) + (ch - '0');
                }
                else if (ch == '-') {
                    sign = -1;
                }
                else if(ch == 'z'){
                  zeroCommand = true;
                }
            }
            procBufCounter++;
        }
        panAngle = ((float)(values[0]))/100;
        tiltAngle = ((float)(values[1]))/100;


       bool panMoved = true, tiltMoved = true;
        stepper_pan.moveTo(panAngle);
        stepper_tilt.moveTo(tiltAngle);
      while (panMoved || tiltMoved) {
        panMoved = stepper_pan.run();
        tiltMoved = stepper_tilt.run();
      }

      if(zeroCommand){
        stepper_pan.reset_positions();
        stepper_tilt.reset_positions();
        zeroCommand = false;
      }


    }

    //////////////////////////////////////////////////////////////////////////////////////

    void setup() {
      stepper_pan.setStepMode(STEP_THIRTYTWO);
      stepper_pan.setSpeed(MOTOR_SPEED);
      stepper_tilt.setStepMode(STEP_THIRTYTWO);
      stepper_tilt.setSpeed(MOTOR_SPEED);
      Serial.begin (BAUD_RATE);
      Serial.flush();
    }

    void loop() {
      if (processString) {
        processCommand(dataBuffer);
        processString = false;
    //     dataBuffer = "";

      }
    }

    void serialEvent() {
      static int dataBufferIndex = 0;
      while (Serial.available() &gt; 0) {
        char incomingbyte = Serial.read();
        if (incomingbyte == startChar) {
          dataBufferIndex = 0;  //Initialize our dataBufferIndex variable
          storeString = true;
        }
        if (storeString) {
          //Let's check our index here, and abort if we're outside our buffer size
          //We use our define here so our buffer size can be easily modified
          if (dataBufferIndex == DATABUFFERSIZE) {
            //Oops, our index is pointing to an array element outside our buffer.
            dataBufferIndex = 0;
            break;
          }
          if (incomingbyte == endchar) {
            dataBuffer[dataBufferIndex] = endchar; //null terminate the C string
            dataBuffer[dataBufferIndex + 1] = '\0';
            //Our data string is complete.  return true
            storeString = false;
            processString = true;
            dataBufferIndex = 0;
          }
          else {
            dataBuffer[dataBufferIndex++] = incomingbyte;
            dataBuffer[dataBufferIndex] = 0; //null terminate the C string
          }
        }

      }

    }
</code></pre>
 24018: <p>I finally figured it out. It is due to reset whenever I open a port for serial communication. Attaching a 10uF capacitor between ground and reset fixed everything.</p>
