bbpystepper.py

""" 
bbpystepper is a Python module used to control a stepper motor via the 
BeagleBone
"""

from __future__ import division
import Adafruit_BBIO.GPIO as GPIO
import time
import math


def initialize_pins(pins):
    for pin in pins:
        GPIO.setup(pin, GPIO.OUT)

def set_all_pins_low(pins):
    for pin in pins:
        GPIO.output(pin, GPIO.LOW)
        
def wavedrive(pins, pin_index):
    for i in range(len(pins)):
        if i == pin_index:
            GPIO.output(pins[i], GPIO.HIGH)
        else:
            GPIO.output(pins[i], GPIO.LOW)

def fullstep(pins, pin_index):
    """pin_index is the lead pin"""
    GPIO.output(pins[pin_index], GPIO.HIGH)
    GPIO.output(pins[(pin_index+3) % 4], GPIO.HIGH)
    GPIO.output(pins[(pin_index+1) % 4], GPIO.LOW)
    GPIO.output(pins[(pin_index+2) % 4], GPIO.LOW)


class Stepper(object):
    def __init__(self, steps_per_rev=2048.0,
                 pins=["P8_13", "P8_14", "P8_15", "P8_16"]):

        self.pins = pins
        
        initialize_pins(self.pins)
        set_all_pins_low(self.pins)
        
        self.angle = 0
        self.steps_per_rev = steps_per_rev
        
        # Initialize stepping mode
        self.drivemode = fullstep
    
    def rotate(self, degrees=360, rpm=15):
        step = 0
        
        # Calculate time between steps in seconds
        wait_time = 60.0/(self.steps_per_rev*rpm)
        
        # Convert degrees to steps
        steps = math.fabs(degrees*self.steps_per_rev/360.0)
        self.direction = 1
        
        if degrees < 0:
            self.pins.reverse()
            self.direction = -1
        
        while step < steps:
            for pin_index in range(len(self.pins)):
                self.drivemode(self.pins, pin_index)
                time.sleep(wait_time)
                step += 1
                self.angle = (self.angle + self.direction/self.steps_per_rev \
                *360.0) % 360.0
        
        if degrees < 0:
            self.pins.reverse()
    	
        set_all_pins_low(self.pins)
        
    def zero_angle(self):
        self.angle = 0
        

def main():
    stepper = Stepper()
    stepper.rotate()
    

if __name__ == "__main__":
    main()