FYI - below is some Arduino code that demonstrates bidirectional operation of a 28BYJ-48 5-Volt stepper motor. It does not use the Arduino library partly because I wanted to get a bit more hands-on with the stepper to learn its operation and partly because the library isn't designed for this type of stepper and the pin assignments need to flipped around to work. Plus, I don't think that the library correctly addresses the eight codes required for this stepper and, instead, uses only four codes. Anyway, this code works well for a functionality demo. The code is based on some general stepper code that I found on the web (I don't recall where) and modified for the 28BYJ-48 stepper. I have also attached a photo of the stepper and interface board that I am using - <$5 for both on eBay. I have also attached a schematic for the ULN2003 Driver Board.
// This Arduino example demonstrates bidirectional operation of a
// 28BYJ-48, which is readily available on eBay, using a ULN2003
// interface board to drive the stepper. The 28BYJ-48 motor is a 4-
// phase, 8-beat motor, geared down by a factor of 68. One bipolar
// winding is on motor pins 1 & 3 and the other on motor pins 2 & 4.
// Refer to the manufacturer's documentation of Changzhou Fulling
// Motor Co., Ltd., among others. The step angle is 5.625/64 and the
// operating Frequency is 100pps. Current draw is 92mA. In this
// example, the speed and direction of the stepper motor is determined
// by adjusting a 1k-ohm potentiometer connected to Arduino pin A2.
// When the potentiometer is rotated fully counterclockwise, the motor
// will rotate at full counterclockwise speed. As the potentiometer is
// rotated clockwise, the motor will continue to slow down until is
// reaches its minimum speed at the the potentiometer's midpoint value .
// Once the potentiometer crosses its midpoint, the motor will reverse
// direction. As the potentiometer is rotated further clockwise, the speed
// of the motor will increase until it reaches its full clockwise rotation
// speed when the potentiometer has been rotated fully clockwise.
////////////////////////////////////////////////
//declare variables for the motor pins
int motorPin1 = 8; // Blue - 28BYJ48 pin 1
int motorPin2 = 9; // Pink - 28BYJ48 pin 2
int motorPin3 = 10; // Yellow - 28BYJ48 pin 3
int motorPin4 = 11; // Orange - 28BYJ48 pin 4
// Red - 28BYJ48 pin 5 (VCC)
int motorSpeed = 0; //variable to set stepper speed
int potPin = 2; //potentiometer connected to A2
int potValue = 0; //variable to read A0 input
//////////////////////////////////////////////////////////////////////////////
void setup() {
//declare the motor pins as outputs
pinMode(motorPin1, OUTPUT);
pinMode(motorPin2, OUTPUT);
pinMode(motorPin3, OUTPUT);
pinMode(motorPin4, OUTPUT);
Serial.begin(9600);
}
//////////////////////////////////////////////////////////////////////////////
void loop(){
potValue = analogRead(potPin); // read the value of the potentiometer
Serial.println(potValue); // View full range from 0 - 1024 in Serial Monitor
if (potValue < 535){ // if potentiometer reads 0 to 535 do this
motorSpeed = (potValue/15 + 5); //scale potValue to be useful for motor
clockwise(); //go to the ccw rotation function
}
else { //value of the potentiometer is 512 - 1024
motorSpeed = ((1024-potValue)/15 + 5); //scale potValue for motor speed
counterclockwise(); //go the the cw rotation function
}
}
//////////////////////////////////////////////////////////////////////////////
//set pins to ULN2003 high in sequence from 1 to 4
//delay "motorSpeed" between each pin setting (to determine speed)
void counterclockwise (){
// 1
digitalWrite(motorPin1, HIGH);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin4, LOW);
delay(motorSpeed);
// 2
digitalWrite(motorPin1, HIGH);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin4, LOW);
delay (motorSpeed);
// 3
digitalWrite(motorPin1, LOW);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin4, LOW);
delay(motorSpeed);
// 4
digitalWrite(motorPin1, LOW);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin4, LOW);
delay(motorSpeed);
// 5
digitalWrite(motorPin1, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin4, LOW);
delay(motorSpeed);
// 6
digitalWrite(motorPin1, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin4, HIGH);
delay (motorSpeed);
// 7
digitalWrite(motorPin1, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin4, HIGH);
delay(motorSpeed);
// 8
digitalWrite(motorPin1, HIGH);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin4, HIGH);
delay(motorSpeed);
}
//////////////////////////////////////////////////////////////////////////////
//set pins to ULN2003 high in sequence from 4 to 1
//delay "motorSpeed" between each pin setting (to determine speed)
void clockwise(){
// 1
digitalWrite(motorPin4, HIGH);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin1, LOW);
delay(motorSpeed);
// 2
digitalWrite(motorPin4, HIGH);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin1, LOW);
delay (motorSpeed);
// 3
digitalWrite(motorPin4, LOW);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin1, LOW);
delay(motorSpeed);
// 4
digitalWrite(motorPin4, LOW);
digitalWrite(motorPin3, HIGH);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin1, LOW);
delay(motorSpeed);
// 5
digitalWrite(motorPin4, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin1, LOW);
delay(motorSpeed);
// 6
digitalWrite(motorPin4, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin2, HIGH);
digitalWrite(motorPin1, HIGH);
delay (motorSpeed);
// 7
digitalWrite(motorPin4, LOW);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin1, HIGH);
delay(motorSpeed);
// 8
digitalWrite(motorPin4, HIGH);
digitalWrite(motorPin3, LOW);
digitalWrite(motorPin2, LOW);
digitalWrite(motorPin1, HIGH);
delay(motorSpeed);
}