controlling a stepper motor with PWM

pwm_stepper_control.ino

/* Teensy LC sketch for controlling a stepper motor.

Reads comma-separate commands over serial.  Sends back number of steps taken.
Commands are of the form:

step,300,800   ->  stepper should move 300 sixteenth-steps forward at 800 steps per second
step,-124,100  ->  stepper should move 124 sixteenth-steps backward at 100 steps per second

*/


// Setup the builtin LED, the step and direction pins.
const int ledPin = 13;
const int stepPin = 3;
const int dirPin = 2;
// Set the PWM duty cycle and counter pin.
const int dutyCycle = 25;
const int counterPin = 9;
// Define step targets and counters.
int stepTarget;
volatile int stepsTaken = 0;
// Store the direction the stepper is moving (one or zero).
int stepperDir;
// Setup command-reading vars.
static char commandBuffer[80];
int commandValue;
int commandFrequency;
// Periodically print status info.
elapsedMillis timeSinceLastPrint;
const int printDelayTime = 1000;


void setup() {
  // Turn on the LED.
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, HIGH);
  // Setup the stepper.
  pinMode(dirPin, OUTPUT);
  digitalWrite(dirPin, LOW);
  pinMode(stepPin, OUTPUT);
  // Setup the counter pin.
  pinMode(counterPin, INPUT_PULLUP);
  attachInterrupt(counterPin, stepInterrupt, RISING);
  // Start serial comms over USB.
  Serial.begin(57600);
}


int readline(int readch, char *commandBuffer, int len) {
  /* Reads chars into a buffer until a carriage return is received.

  Method via hackingmajenkoblog.wordpress.com
  */
  static int pos = 0;
  int rpos;
  if (readch > 0) {
    switch (readch) {
      // Ignore new lines but return on CR.
      case '\n':
        break;
      case '\r':
        rpos = pos;
        pos = 0;
        return rpos;
      default:
        if (pos < len-1) {
          commandBuffer[pos++] = readch;
          commandBuffer[pos] = 0;  // ??
        }
    }
  }
  // No end of line has been found, so return -1.
  return -1;
}



void loop() {
  // Try to read a command.
  if (readline(Serial.read(), commandBuffer, 80) > 0) {
    if (sscanf(commandBuffer, "step,%d,%d", &commandValue, &commandFrequency) == 2) {
      // If the stepping command is valid, apply it.
      if (commandValue > 0) {
        digitalWrite(dirPin, HIGH);
        stepperDir = 1;
      } else {
        digitalWrite(dirPin, LOW);
        stepperDir = -1;
      }
      analogWriteFrequency(stepPin, commandFrequency);
      stepTarget = stepsTaken + commandValue;
      analogWrite(stepPin, dutyCycle);

    } else {
      Serial.print("Error: received message '");
      Serial.print(commandBuffer);
      Serial.println("'");
    }
  }

  // Stop the stepper when it reaches its step target.
  if (stepperDir == 1 && stepsTaken >= stepTarget) {
    analogWrite(stepPin, 0);
  }
  else if (stepperDir == -1 && stepsTaken <= stepTarget) {
    analogWrite(stepPin, 0);
  }

  // Periodically print the stepper position.
  if (timeSinceLastPrint > printDelayTime) {
    Serial.println(stepsTaken);
    timeSinceLastPrint = 0;
  }
}


// Setup counter interrupt.  Increment the count in a direction-sensitive way.
void stepInterrupt() {
  stepsTaken += stepperDir;
}

@ruizanthony -- it's a builtin if you use the teensy libs, same with ellapsedMillis