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Easy Basics Project 004a 28 BYJ - 48 Stepper Motor

of Acoptex.com in UNO

Basics: Project 004a

Project name: 28 BYJ - 48 Stepper Motor

Attachments: libraries and program

In this project, you needed these parts :

1.Aruduino Uno R3 (you can also use the other version of Arduino)

2.BYJ 48 Stepper Motor

3.Arduino IDE ( you can download it from here  )

4.Jumper cables

5.ULN2003 stepper motor driver board

Understanding the stepper motors

A stepper motor is a motor controlled by a series of electromagnetic coils. The center shaft has a series of magnets mounted on it, and the coils surrounding the shaft are alternately given current or not, creating magnetic fields which repulse or attract the magnets on the shaft, causing the motor to rotate.

This design allows for very precise control of the motor: by proper pulsing, it can be turned in very accurate steps of set degree increments (for example, two-degree increments, half-degree increments, etc.). They are used in printers, disk drives, and other devices where precise positioning of the motor is necessary.

There are two basic types of stepper motors, unipolar steppers and bipolar steppers.

Unipolar Stepper Motors

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 motors

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).

Like other motors, stepper motors require more power than a microcontroller can give them, so you’ll need a separate power supply for it. Ideally you’ll know the voltage from the manufacturer, but if not, get a variable DC power supply, apply the minimum voltage (hopefully 3V or so), apply voltage across two wires of a coil (e.g. 1 to 2 or 3 to 4) and slowly raise the voltage until the motor is difficult to turn. It is possible to damage a motor this way, so don’t go too far. Typical voltages for a stepper might be 5V, 9V, 12V, 24V. Higher than 24V is less common for small steppers, and frankly, above that level it’s best not to guess.

To control the stepper, apply voltage to each of the coils in a specific sequence. The sequence would go like this:

Step wire 1 wire 2 wire 3 wire 4
1 High low high low
2 low high high low
3 low high low high
4 high low low high

To control a unipolar stepper, you use a Darlington Transistor Array. The stepping sequence is as shown above. Wires 5 and 6 are wired to the supply voltage.

To control a bipolar stepper motor, you give the coils current using to the same steps as for a unipolar stepper motor. However, instead of using four coils, you use the both poles of the two coils, and reverse the polarity of the current.

The easiest way to reverse the polarity in the coils is to use a pair of H-bridges. The L293D dual H-bridge has two H-bridges in the chip, so it will work nicely for this purpose.

Once you have the motor stepping in one direction, stepping in the other direction is simply a matter of doing the steps in reverse order.

Knowing the position is a matter of knowing how many degrees per step, and counting the steps and multiplying by that many degrees. So for examples, if you have a 1.8-degree stepper, and it’s turned 200 steps, then it’s turned 1.8 x 200 degrees, or 360 degrees, or one full revolution.

Two-Wire Control

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 middle wires of the sequence above:

Step wire 1 wire 2
1 low high
2 high high
3 high low
4 low low

The circuits for two-wire stepping are as follows:

Unipolar stepper two-wire circuit:

Biolar stepper two-wire circuit:


Because both unipolar and bipolar stepper motors are controlled by the same stepping sequence, we can use the same microcontroller code to control either one. In the code examples below, connect either the Darlington transistor array (for unipolar steppers) or the dual H-bridge (for bipolar steppers) to the pins of your microcontroller as described in each example. There is a switch attached to the microcontroller as well. When the switch is high, the motor turns one direction. When it’s low, it turns the other direction.

We will use unipolar stepper motor 28BYJ-48 for this project.

There are many types of drivers - L293, ULN2003, A3967SLB and more. 

The 28BYJ-48 even comes with breakout using ULN2003 as a motor driver chip.

Datasheet can be found here.

Signals and contacts stepper motor and ULN2003

Note: if you want to use L293 instead of ULN2003 you will need to leave Red wire No connection.

Wiring

The following table and picture shows the needed connections with the Arduino Uno.

The following table and picture shows the needed connections with the Chinese Uno.

Step by Step instruction

  1. Plug your Adruino Uno board into your PC and select the correct board and com port
  2. You must take something in consider: 28BYJ-48 has a gear ratio of 64 and stride angle 5.625 so this motor has a 4096 Steps. Number of Steps in one revolution= 360/stride angle=360/5.625=64. Steps =Number of steps in One Revolution * Gear ratio. Steps= (360/5.625)*64 = 64 * 64 =4096 - this value will substitute it in the arduino sketch. 
  3. For Adafruit Stepper Motor the stride angle 7.5 and gear ratio is 16. So number of steps in 1 revolution will be : steps in One Revolution  = 360 / 7.5 = 48. Steps= 48 * 16 = 768. It will be different depending on what motor you are using so check the datasheet for your stepper motor to calibrate these values.
  4. Verify and upload the the sketch to your Adruino Uno.

 

Libraries:

  • See attachments on the begining of this project description.
  • The Stepper library included in Adruino IDE program which installed in your PC.

 

Program/Sketch

/********************************
* name: BYJ48 Stepper motor code
* function: This program drives a unipolar or bipolar stepper motor. 
            The motor moves 1000 steps in one direction, then 1000 in the other.
********************************/
//Email:info@acoptex.com
//Website:www.acoptex.com
/********************************/
// include the library code
#include <Stepper.h>
/********************************/
#define motorSteps 64     // change this depending on the number of steps
                           // per revolution of your motor
#define motorPin1 8
#define motorPin2 10
#define motorPin3 9
#define motorPin4 11
/********************************/
// initialize of the Stepper library:
Stepper myStepper(motorSteps, motorPin1,motorPin2,motorPin3,motorPin4); 
/********************************/
void setup() {
  // set the motor speed at 200 RPMS:
  myStepper.setSpeed(200);
  // Initialize the Serial port:
  Serial.begin(9600);
}
/********************************/
void loop() {
  // Step right 1000 steps:
  Serial.println("Turn right");
  myStepper.step(1000);
  delay(500);
  // Step left 100 steps:
  Serial.println("Turn left");
   myStepper.step(-1000);
  delay(500);
 }



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Published at 30-04-2017
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