Stepper motor interfacing with Microcontrollers tutorial

►Introduction

        This section of tutorial will explain you everything that you need to know about stepper motors. Stepper motors can be used in various areas of your microcontroller projects such as making robots, robotic arm, and automatic door lock System etc. This tutorial will explain you construction of stepper motors (unipolar and bipolar stepper motors ), basic principle, different controlling types (Half step and Full step), Interfacing Techniques (using L293D or ULN2003) and programming your microcontroller in C and assembly to control stepper motor.

►Unipolar stepper motor

        The unipolar stepper motor has five or six wires and four coils (actually two coils divided by center connections on each coil). The center connections of the coils are tied together and used as the power connection. They are called unipolar steppers because power always comes in on this one pole.

►Bipolar stepper motor

        The bipolar stepper motor usually has four wires coming out of it. Unlike unipolar steppers, bipolar steppers have no common center connection. They have two independent sets of coils instead. You can distinguish them from unipolar steppers by measuring the resistance between the wires. You should find two pairs of wires with equal resistance. If you've got the leads of your meter connected to two wires that are not connected (i.e. not attached to the same coil), you should see infinite resistance (or no continuity).

        As already said, we will talk mostly on "Unipolar stepper motors" which is most common type of stepper motor available in the market.A simple example of 6 lead step motor is given below and in 5 lead step motor wire 5 and 6 are joined together to make 1 wire as common.

►Working of Stepper Motor

         Now let’s discuss the operation Principle of a stepper motor. When we energize a coil of stepper motor, the shaft of stepper motor (which is actually a permanent magnet) align itself according to poles of energized coil. So when motor coils are energized in a particular sequence, motor shaft tend to align itself according to pole of coils and hence rotates. A small example of energizing operation is given below.

You can see in the example, when coil "A" is energized, A north-south polarity is generated at "A+A\" as shown in the figure above and magnetic shaft automatically align itself according to the poles generated. When the next coil is energized the shaft again aligns itself and takes a step. Hence the working pricipal.

We have seen that to make the stepper motor work, we need to energize coil in a sequence. The explanation and generation of the sequence is explained below.

Step Sequence:

Stepper motors can be driven in two different patterns or sequences. Namely,

• Full Step Sequence

• Half Step Sequence

we will go through theses equences one by one.

►Full Step Sequence

In the full step sequence, two coils are energized at the same time and motor shaft rotates. The order in which coils has to be energized is given in the table below

Full Mode Sequence 

Step          A        B        A\        B\

 0             1         1        0          0

      1             0         1        1           0   

   2             0         0        1          1

    3               1         0         0         1

The working of the full mode sequence is given in the animated figure below.

►Half Step Sequence

        In Half mode step sequence, motor step angle reduces to half the angle in full mode. So the angualar resolution is also increased i.e. it becomes double the angular resolution in full mode. Also in half mode sequence the number of steps gets doubled as that of full mode. Half mode is usually preffered over full mode. Table below shows the pattern of energizing the coils.

Half Mode Sequence

Step         A         B         A\          B\

  0             1         1          0             0

  1             0         1          0             0

  2            0          1          1             0  

  3            0          0          1            0

  4            0          0          1            1

  5            0          0          0            1

  6            1          0           0            1

  7            1          0           0            0



The working of the half mode sequence is given in the animated figure below.

 

►Step Angle

         

          Step angle of the stepper motor is defined as the angle traversed by the motor in one step. To calculate step angle,simply divide 360 by number of steps a motor takes to complete one revolution. As we have seen that in half mode, the number of steps taken by the motor to complete one revolution gets doubled, so step angle reduces to half.

As in above examples, Stepper Motor rotating in full mode takes 4 steps to complete a revolution, So step angle can be calculated as...

Step Angle ø = 360° / 4 = 90°

and in case of half mode step angle gets half so 45°.

So this way we can calculate step angle for any stepper motor. Usually step angle is given in the spec sheet of the stepper motor you are using. Knowing stepper motor's step angle helps you calibrate the rotation of motor also to helps you move the motor to correct angular position.

►Step Sequence for 2-wire control of Unipolar stepper motor

         

           As seen in above explanation, In every step of the sequence, two wires are always set to opposite polarities. Because of this, it's possible to control steppers with only two wires instead of four, with a slightly more complex circuit. The stepping sequence is the same as it is for the two coils A and B, and the opposite polarity value is given to A\ and B\. The sequence is given in the table below:

2-wire Mode Sequence

Step         A        B

  0            0         1

  1              1         1

  2              1         0

  3              0         0

►Step Sequence for Bipolar stepper motor

         Bipolar motor has simpler construction. It has two windings with no center taps and a permanent magnet at the center just like unipolar stepper motors. Being simpler in construction, the stepping sequence is a little complex, as the power for both the coils has to be controlled in such a way that the polarity of the poles get reversed. This polarity sequence is shown in the table below.

Polarity Sequence

Step        A        A\        B         B\

 

0           +ve     -ve      -ve      -ve

 

1            -ve     -ve      +ve      -ve
 

     2            -ve     +ve      -ve      -ve    

3           -ve     -ve     -ve    +ve

The above polarity sequence can be interpreted in terms of logic levels for microcontroller by activating one coil at a time as shown in the table below.

Step Sequence

Step        A       A\       B        B\

 0              1        0          0          0

 1              0        0          1           0

 2              0        1          0           0

 3              0        0          0           1

We have now learnt most of the necessary things regarding a stepper motor. In the next section we will discuss about the various techniques to interface a stepper motor.

►Connecting Unipolar Stepper Motor

        

      There are actually many ways you can interface a stepper motor to your controller, out of them the most used interfaces are:

•  Interface using L293D - H-Bridge Motor Driver
• Interface using ULN2003/2004 - Darlington Arrays

We will dicuss both connection techniques one by one. The above mentioned methods need 4 controller pins for interface.

►Connecting Unipolar stepper using L293D

 
As you see in the circuit above the four pins "Controller pin 1",2,3 and 4 will control the motion and direction of the stepper motor according to the step sequence programmed in the controller.

►Connecting Unipolar stepper using ULN2003/2004

As already discussed in case of L293D, Here in this circuit too the four pins "Controller pin 1",2,3 and 4 will control the motion and direction of the stepper motor according to the step sequence sent by the controller.

►2-wire connection for Unipolar Stepper Motor

          We have seen the generally used 4-wire connection method for interfacing unipolar stepper motor, but we can simplify the design to make controller use less pins with the help of 2-wire connection method. The circuit for 2-wire connection is shown below.

►Connecting Bipolar Stepper Motors

        we have studied that, Bi-polar stepper motors has 2 different coils. The step sequence for bipolar stepper motor is same as that of unipolar stepper motors. The driving circuits for this require an H-Bridge as it allows the polarity of the power applied to be controlled independently. This can be done as shown in the figure below:

Now we have seen the methods for connecting stepper motors with your microcontroller. So keeping these circuits in mind, we will now look at the programming of microcontroller to control stepper motors. This is discussed in the next section of the tutorial.

 
►Programming Full step Sequence

►C Programming

         I am assuming that stepper motor is connected at Port 1.0 to Port 1.3. Adjusting the delay will increase or decrease the speed of the motor. Here just for demonstration i have taken some delay, you can change it as you want.

CODE:

#include

#define stepper P1

void delay();

void main()

{

        while(1)

        {

                  stepper = 0x0C;

                  delay();

                  stepper = 0x06;

                  delay();

                  stepper = 0x03;

                  delay();

                  stepper = 0x09;

                  delay();

        }

}

void delay()

{

         unsigned char i,j,k;
         for(i=0;i<6;i++)>

               for(j=0;j<255;j++)>

                     for(k=0;k<255;k++);

}

►Assembly Programming

CODE:
               org 0H

               stepper equ P1

main:
               mov stepper, #0CH
               acall delay
               mov stepper, #06H
               acall delay
               mov stepper, #03H
               acall delay
               mov stepper, #09H
               acall delay
               sjmp main

delay:
               mov r7,#4
wait2:
               mov r6,#0FFH
wait1:
               mov r5,#0FFH
wait:
               djnz r5,wait
               djnz r6,wait1
               djnz r7,wait2
               ret
               end


The working of the above code can be seen in the demo animation below.

►Programming Half step Sequence

►C Programming

Just the main routine changes rest everything remains same, i mean same delay routine.

CODE:

void main()

{
        while(1)

       {
                stepper = 0x08;
                delay();
                stepper = 0x0C;
                delay();
                stepper = 0x04;
               delay();
               stepper = 0x06;
               delay();
               stepper = 0x02;
               delay();
               stepper = 0x03;
               delay();
               stepper = 0x01;
               delay();
               stepper = 0x09;
               delay();
       }
}

►Assembly Programming

Here also the main routine changes rest everything remains same.

CODE:

main:
             mov stepper, #08H
             acall delay
             mov stepper, #0CH
             acall delay
             mov stepper, #04H
             acall delay
             mov stepper, #06H
             acall delay
             mov stepper, #02H
            acall delay
            mov stepper, #03H
            acall delay
            mov stepper, #01H
            acall delay
            mov stepper, #09H
            acall delay
            sjmp main


The working of the above code can be seen in the demo animation below.

►Programming for 2-wire connection of Unipolar Stepper Motor

►C Programming

CODE:

void main()

{
           while(1)

           {

                      stepper = 0x03;
                     delay();
                     stepper = 0x01;
                     delay();
                     stepper = 0x00;
                    delay();
                    stepper = 0x02;
                    delay();
           }
}

►Assembly Programming

CODE:

main:
              mov stepper, #03H
              acall delay
              mov stepper, #01H
              acall delay
              mov stepper, #00H
              acall delay
              mov stepper, #02H
              acall delay
              sjmp main

The working of the above code can be seen in the demo animation below.

►Programming for Bipolar Stepper Motor

►C Programming

CODE:

void main()

{
           while(1)

          {
                     stepper = 0x08;
                     delay();
                     stepper = 0x02;
                     delay(); 
                     stepper = 0x04;
                    delay();
                    stepper = 0x01;
                    delay();
           }
}

►Assembly Programming

CODE:

main:
                mov stepper, #08H
                acall delay
                mov stepper, #02H
                acall delay
                mov stepper, #04H
                acall delay
                mov stepper, #01H
                acall delay
                sjmp main