9

FORGE

Left

Simplified coil wiring

schemes for unipolar

(left) and bipolar

(right) stepper

motors. Bipolar

motors are often

used in 3D printers

and laser cutters

Figure 1

Wiring up the

28BYJ-48 circuit to

the Arduino and driver

is simple – six wires

and one plug to fit

complicated, needing two full H-bridges to be able to
reverse the current direction in each coil. Fortunately,
due to the huge growth in 3D printing and CNC
machinery, there are some relatively inexpensive
solutions available to drive bipolar steppers. The
Allegro A4988-based ‘stepstick’ driver board is a very
popular, inexpensive choice (£1–2 on eBay). As to
the motors themselves, the NEMA 17-sized bipolar
steppers, commonly used in 3D printers, can be
found on eBay from £5.

28BYJ-48 USAGE
The 28BYJ-48 is a small, low power, 5 V stepper with
32 full steps per rotor revolution. The rotor shaft
is connected to a 64:1 reduction gearbox which
transforms it into a 2048 step motor, and gives it a
reasonable amount of torque for a low power motor.
It’s ideal for small robots, hobby projects, and
educational use because it’s small, cheap, easy to
wire, and can run from the Arduino 5 V rail, with no
extra external PSU.
The main disadvantage is that the gearbox slows
down the maximum output shaft rotational speed to
at least 8 rpm.
Connect up your wiring according to the
circuit diagram – Figure 1, below.

Using the Arduino IDE on your computer,

flash the sketch Nano_stepper_28BYJ-48.ino

(hsmag.cc/xLXbny) to your Arduino, and make

sure that the jumper on the ULN2003 driver board is

attached (this connects the motor to the +5 V rail).

If everything goes according to plan, your motor

should rotate alternately 360° clockwise, then 360°

anti-clockwise, with one second pauses, until you

remove the power.

CRACKING THE CODE

Next up comes the coding:

#include <Stepper.h>

#define Steps_per_motor_revolution 32

#define Steps_per_output_revolution 32 * 64

int Steps_travel;

Lines 1–4 load the built-in Arduino Stepper

library and initialise some variables. Note that

motor_revolution and output_revolution are not the

same thing as we have a 64:1 reduction gearbox.

Stepper small_stepper(Steps_per_motor_revolution,

11, 9, 10, 8);

YOU’LL NEED

28BYJ-48 stepper

motor and

ULN3008 driver

(eBay)

NEMA 17-style

bipolar stepper

motor

A4988 ‘stepstick’

driver board

(eBay)

8–12 V power

source

Arduino Nano or

compatible board

Breadboard

and wires

100 μF

electrolytic

capacitor

ROTOR

ROTOR

UNIPOLAR BIPOLAR

5 Wire 4 Wire