Another frustrating issues that can take days to resolve.
Here are a few issues I have been facing and the solutions I cam up with. I hope this helps others in long frustrations.
Stepper motor 28BYJ-48 12V with external power
ULN2003A drive
Challenge 1
ULN led lights blink, motor does not move.
Solution: reduce speed from 1 to 130 max.
if(speed > 130) speed = 130; //for safety and test proper max speed with your motor
Challenge 2
Motor acts funny and does not move to right position regardless of the number of steps
Solution: loop around single step. It is slower but guarantee to work.
for(i = 0; i <= numOfSteps; i++) StepMotor1.step(1);
Challenge 3
Motor only goes clockwise no matter what.
Solution discovered in another forum post, interchange pin 2 with pin 3
Stepper StepMotor1(steps, Pin1, Pin3, Pin2, Pin4); //yet on board corresponding wires are sequential.