raspberry pi

Controlling of stepper motor through Pi

The basic idea of using stepper motor here goes back to its variety of its usages in robotics applications. Coming straight to our project i.e. how to control a stepper motor using Raspberry Pi?
Broadly, the project is divided into two parts:

interfacing GPIO pins with the stepper motor
python script

Raspberry PI GPIO pinout

INTERFACING WITH PI

STEP1:

CONNECT IN A WITH PIN11 (GPIO 17)

STEP2:

CONNECT IN B WITH PIN12 (GPIO 18)

STEP3:

CONNECT IN C WITH PIN13(GPIO 21)

STEP4:

CONNECT IN D WITH PIN15(GPIO 22)

STEP5:

CONNECT 5V WITH PIN6(GND) AND PIN2(+5V)

The motor connects to the controller board with a pre-supplied connector. The controller board has 4+2 pins that need to be connected to the Pi header (P1).

The P1-XX references above represent the Pi header pins I used. These are defined in the Python example below in the StepPins list so if you use different pins be sure to update the Python list as well. You can use other GPIO pins if required just remember to update your Python script.

Python script

Here is a copy of the script I used to rotate the stepper motor. It uses version 0.2.0 of the RPi.GPIO library and defines a 4-step and 8-step sequence.

 
# Import required libraries

import time

import RPi.GPIO as GPIO

# Use BCM GPIO references

# instead of physical pin numbers

GPIO.setmode(GPIO.BCM)

# Define GPIO signals to use

# Pins 18,22,24,26

# GPIO24,GPIO25,GPIO8,GPIO7

StepPins = [24,25,8,7]

# Set all pins as output

for pin in StepPins:

  print "Setup pins"

  GPIO.setup(pin,GPIO.OUT)

  GPIO.output(pin, False)

# Define some settings

StepCounter = 0

WaitTime = 0.5

# Define simple sequence

StepCount1 = 4

Seq1 = []

Seq1 = range(0, StepCount1)

Seq1[0] = [1,0,0,0]

Seq1[1] = [0,1,0,0]

Seq1[2] = [0,0,1,0]

Seq1[3] = [0,0,0,1]

# Define advanced sequence

# as shown in manufacturers datasheet

StepCount2 = 8

Seq2 = []

Seq2 = range(0, StepCount2)

Seq2[0] = [1,0,0,0]

Seq2[1] = [1,1,0,0]

Seq2[2] = [0,1,0,0]

Seq2[3] = [0,1,1,0]

Seq2[4] = [0,0,1,0]

Seq2[5] = [0,0,1,1]

Seq2[6] = [0,0,0,1]

Seq2[7] = [1,0,0,1]

# Choose a sequence to use

Seq = Seq1

StepCount = StepCount1

# Start main loop

while 1==1:

  for pin in range(0, 4):

    xpin = StepPins[pin]

    if Seq[StepCounter][pin]!=0:

      print " Step %i Enable %i" %(StepCounter,xpin)

      GPIO.output(xpin, True)

    else:

      GPIO.output(xpin, False)

  StepCounter += 1

  # If we reach the end of the sequence

  # start again

  if (StepCounter==StepCount):

    StepCounter = 0

  if (StepCounter<0):

    StepCounter = StepCount

  # Wait before moving on

  time.sleep(WaitTime)

In this example the wait time is set to 0.5 seconds. To make the motor turn faster you can reduce this value. I found I could reduce it to 0.004 before the motor stopped working. If the script runs too fast the motor controller can’t keep up. This performance may vary depending on your motor and its controller.

The 4 step sequence is faster but the torque is lower. It’s easy to stop the rotation by holding the motor spindle. The 8 step sequence is slower but the torque is much higher. For my turntable application I prefer the torque over speed so I will be using the 8 step sequence.