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#431 Driving the 28BYJ-48 Unipolar Stepper

All about the 28BYJ-48 unipolar stepper motor and driving it with an Arduino.


Here’s a quick demo..



The 28BYJ-48 stepper motor is pretty common in Arduino kits, and available from various suppliers on aliexpress, often supplied with an “X113647” ULN2003A driver board.

It is a 5-wire unipolar motor that runs at 5V and is suitable for cases where higher precision and torque are required, but not high rotational speed.

Driving Unipolar Stepper Motors

Unipolar stepper motors are simpler to drive than bipolar motors because no current reversal is required. This makes them very easy to control from a microprocessor platform like an Arduino, as they just require assistance to switch a higher current/voltage circuit with GPIO pins. The ULN2003A darlington transistor array is commonly used for this.

Some reasoures:

DroneBot Workshop has an excellent introduction to driving stepper motors, including the 28BYJ-48:


The essential full-step sequence:


The 28BYJ-48 Stepper Motor

The 28BYJ-48 is a 5-wire unipolar stepper motor.

Item Spec Notes
Voltage 5V  
Current 130mA - 250mA just based on some measurements I made while running the motor
Steps/revolution 32  
Gears 64:1 reduction because of the gearing, high speeds are not possible, but it does deliver substantial torque

As with most motors, the power required is too much to pull directly from an Arduino, so a separate power supply is required but with a common ground.

The 28BYJ-48 or similar steper motors are available from multiple sources, and there are two important things to note:

  • wiring colors are not always consistent - I’ve seen at least two different color sequences used.
  • but - almost? - always, the phase sequence is the same at the connector, but it is an order that requires re-mapping to the standard sequence used by the Stepper library (more on this later).

A good technical resources for the 28BYJ-48 is the geeetech page. Gaven MacDonald also has a good 28BYJ-48 teardown here:


The windings of the 28BYJ-48 are usually documented like this:


However, this may be a bit confusing as it doesn’t really represent how the windings energize the poles/teeth of the stator. Specifically (at least on the motor unit I have) the clockwise activation sequence is: Blue -> Pink -> Yellow -> Orange.

This translates to a full-step sequence:

Step Blue Pink Yellow Orange
1 1 1    
2   1 1  
3     1 1
4 1     1


  • Clockwise step sequence: 1-2-3-4
  • Counter-clockwise step sequence: 4-3-2-1
  • Red (common) is positive
  • indicates which pins are to be grounded; the ULN2003A inverts logic i.e IN1 pulled high in order to ground OUT1/Blue

A half-step sequence simply interleaves transitional steps with only one coil activated:

Step Blue Pink Yellow Orange
1 1 1    
2   1    
3   1 1  
4     1  
5     1 1
6       1
7 1     1
8 1      

It is possible (although not very practical) to do a “double step” sequence with just two coils. This is useful for proving which pairs are opposing.


Step Blue Pink Yellow Orange
1 1      
2     1  


Step Blue Pink Yellow Orange
1   1    
2       1

The X113647 Driver Board

A driver board is usually supplied with the 28BYJ-48. There are various versions - I have one identfiied as X113647 - but they all essentially do the same thing:

  • provide a breakout for the ULN2003A Darlington transistor array
  • map four inputs (IN1-4) to the 28BYJ-48 motor connector
  • link common ground between Arduino and the stepper motor
  • provide the external power connector - with jumper to disable, and a decoupling capacitor
Controller-side Stepper-side 28BYJ-48
IN1 OUT1 Blue
IN2 OUT2 Pink
IN3 OUT3 Yellow
IN4 OUT4 Orange
- COM: 5-12V Red

The X113647

Direct Drive Example

The DirectDrive.ino sketch is an example of low-level driving the 28BYJ-48 motor via the X113647 board.

It does not use any libraries, but rather explicity controls the 4 pins.

It runs three demo sequences in order, then repeats:

  • full step, one full rotation clockwise and then back
  • half-full step, one full rotation clockwise and then back
  • double-full step, one full rotation clockwise and then back

Stepper Library Example

The StepperLibraryDrive.ino sketch is an example of driving the 28BYJ-48 motor/X113647 board with the standard Stepper library.

When using the standard Stepper library:

  • pins must be mapped to a 1-3-2-4 sequence to work correctly
  • only full-step drive is possible

To clarify the “mapping” requirement: given the sequence required by the 28BYJ-48 is:

Step Blue Pink Yellow Orange
1 1 1    
2   1 1  
3     1 1
4 1     1

And the Stepper Library implements the following sequence:

Step C0 C1 C2 C3
1 1 0 1 0
2 0 1 1 0
3 0 1 0 1
4 1 0 0 1

Then it is readily observed that switching Pink/Yellow (C1/C2) aligns things nicely, so we end up with a pin mapping for initializing the Stepper library as follows:



If you use Fritzing, it is annoying not to have parts available for these common stepper components! After searching high and low and not finding anything already available, I tried my hand at creating some custom parts (using the new part formats - most recently tested with Fritzing 0.9.0b06.11). Note that these parts are not suitable for etching your own stepper drive board, but they do work nicely enough for drawing circuits involving and X113647 or 28BYJ-48 components.

With these parts you can draw stepper motor circuits like this canonical hookup of the X113647 and 28BYJ-48 to an Arduino Uno, with external power supply for the motor. In this case, the breadboard is just a glorified cable connector.



Note the crossover of the wires eminating from the 28BYJ-48. This is actually done in the wiring of the standard connector provided with the stepper motor - but I haven’t included this detail in the part as yet.


Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.