#431 Driving the 28BYJ-48 Unipolar Stepper

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

Build

Here’s a quick demo..

Notes

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:

The Adafruit guide to choosing and using stepper motors
Robot Builder’s Bonanza - Working with Stepper Motors Bonus Chapters From RBB Fourth Edition

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:

28BYJ48_windings

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

Note:

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.

Clockwise:

Step	Blue	Pink	Yellow	Orange
1	1
2			1

Counter-clockwise:

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
GND	GND	-

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:

Stepper myStepper(STEPS_PER_REVOLUTION, PIN_IN1_BLUE, PIN_IN3_YELLOW, PIN_IN2_PINK, PIN_IN4_ORANGE);

Construction

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.

28BYJ-48 Stepper Motor
X113647 Stepper Driver Board is a part for the board.

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.

Breadboard

Schematic

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.