Arduino digital pins only output 1.8V?

I built 28 byj-40 stepper control circuit using ULN2003 from scratch. The stepper is powered using 4 AA batteries (5V~) and the Arduino is powered from my PC.

The stepper runs correctly and only gets warm, never gets hot even after 30 min. The ULN2003 stays cool despite being a relatively inefficient driver. I guess this is because my total power is low? I measured the battery current and it’s only 200mA at max.

However, I measured the voltage at the output pins of the Arduino and it’s only around 1.8V. I wonder if this is because the voltage fluctuates too fast and my multimeter takes only the “average value.” ???

I used the Accelstepper library:

#include <AccelStepper.h>
#define HALFSTEP 8

// Motor pin definitions
#define motorPin1 3 // IN1 on the ULN2003 driver 1
#define motorPin2 4 // IN2 on the ULN2003 driver 1
#define motorPin3 5 // IN3 on the ULN2003 driver 1
#define motorPin4 6 // IN4 on the ULN2003 driver 1

// Initialize with pin sequence IN1-IN3-IN2-IN4 for using the AccelStepper with 28BYJ-48
AccelStepper stepper1(HALFSTEP, motorPin1, motorPin3, motorPin2, motorPin4);

void setup() {
pinMode(motorPin1, OUTPUT);
pinMode(motorPin2, OUTPUT);
pinMode(motorPin3, OUTPUT);
pinMode(motorPin4, OUTPUT);
stepper1.setMaxSpeed(3000.0);
stepper1.setAcceleration(50.0);
stepper1.setSpeed(5);
stepper1.moveTo(5550);

}//–(end setup )—

void loop() {

//Change direction when the stepper reaches the target position
if (stepper1.distanceToGo() == 0) {
stepper1.moveTo(-stepper1.currentPosition());
}
stepper1.run();
}

I tested the pins using the blinker sketch and it outputs 5V, so we know the Arduino is fine. I then tested it using a different code for the stepper, one that does not use the Accelstepper library, and the output pin voltage fluctuates but I can see 4.5V from time to time:

#include <Stepper.h>

/-----( Declare Constants, Pin Numbers )-----/
//—( Number of steps per revolution of INTERNAL motor in 4-step mode )—
#define STEPS_PER_MOTOR_REVOLUTION 32

//—( Steps per OUTPUT SHAFT of gear reduction )—
#define STEPS_PER_OUTPUT_REVOLUTION 32 * 64 //2048

/-----( Declare objects )-----/
// create an instance of the stepper class, specifying
// the number of steps of the motor and the pins it’s
// attached to

//The pin connections need to be pins 8,9,10,11 connected
// to Motor Driver In1, In2, In3, In4

// Then the pins are entered here in the sequence 1-3-2-4 for proper sequencing
Stepper small_stepper(STEPS_PER_MOTOR_REVOLUTION, 3, 5, 4, 6);

/-----( Declare Variables )-----/
int Steps2Take;

void setup() /----( SETUP: RUNS ONCE )----/
{
// Nothing (Stepper Library sets pins as outputs)
}/–(end setup )—/

void loop() /----( LOOP: RUNS CONSTANTLY )----/
{

Steps2Take = STEPS_PER_OUTPUT_REVOLUTION *.5; // Rotate CW 1/2 turn
small_stepper.setSpeed(500);
small_stepper.step(Steps2Take);
delay(10);

Steps2Take = - STEPS_PER_OUTPUT_REVOLUTION * .5; // Rotate CCW 1/2 turn
small_stepper.setSpeed(500); // 700 a good max speed??
small_stepper.step(Steps2Take);
delay(10);

}/* --(end main loop )-- */

So does anyone know the output voltage stays a constant 1.8ish on the multimeter when I used the Accelstepper library?

Thanks

"I measured the voltage at the output pins of the Arduino and it's only around 1.8V"

You do need an oscilloscope to look at changing signals.

.

Digital multimeters use an integrating ADC that is extremely slow, maybe a few samples per second. That's far too slow to pick out the individual pulses of the output voltage, so it just ends up getting averaged.