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https://github.com/IDWizard/uln2003

Micropython code to drive stepper motors via ULN2003
https://github.com/IDWizard/uln2003

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Micropython code to drive stepper motors via ULN2003

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# uln2003

Micropython code to drive stepper motors via ULN2003



This is the ongoing work of my experiments with the BBC micro:bit and some ULN2003 stepper motors connected to 5V 28BYJ-48 Stepper Motors.



## Materials



You will need:



1. A micro:bit with USB cable (and a computer to connect it to!)

1. A 5V DC power source

1. One or more 28BYJ-48 stepper motors with matching ULN2003 driver boards

1. Wires, lots of wires.

1. (Optional but handy) A breakout board to make accessing the bit's IO pins easier



## Wiring / Connecting



1. Plug the stepper motor into the ULN2003

1. Connect the 4 pins from the ULN2003 into 4 separate I/O pins of the bit

1. Connect the 5v input +/- on the ULN2003 to a 5v source +/- terminals

1. Connect the bit to the computer

1. Load up the library and push to the bit (i.e. compile the program and upload to the bit)



## Using the library



Code example:



```python

# Create a stepper using the HALF_STEP command sequence 

# to a stepper which is connected:

#                     micro:bit    ULN2003

#                     pin16     -> INP1 

#                     pin15     -> INP2

#                     pin14     -> INP3

#                     pin13     -> INP4

# Set the delay between steps to 5 microseconds



s1 = Stepper(HALF_STEP, microbit.pin16, microbit.pin15, microbit.pin14, microbit.pin13, delay=5)  

s1.step(100)     # Rotate 100 steps clockwise



s1.step(100, -1) # Rotate 100 steps anti-clockwise

```



A delay of less than 5 microseconds may cause the motor to simply buzz and not move at all. Try and see what works for you and your motors.



Because of the gearing of this motor a full rotation isn't very exact. It is somewhere between 508 and 509 steps. The constant FULL_ROTATION has a value of int(4075.7728395061727 / 8) = ~509 steps.



## Advanced Usage (Driving more than 1 stepper motor)



Being able to drive a stepper is cool but the bit has a lot more IO pins. It's possible to drive two steppers:



```python

s1 = Stepper(HALF_STEP, microbit.pin16, microbit.pin15, microbit.pin14, microbit.pin13, delay=5)    

s2 = Stepper(HALF_STEP, microbit.pin6, microbit.pin5, microbit.pin4, microbit.pin3, delay=5)   

s1.step(FULL_ROTATION)

s2.step(FULL_ROTATION)

```



But you will notice that this makes stepper1 move a full circle (or a teensy bit more than a full circle) and then stepper2 will move a full circle. 



If you want to move both motors at the same time then you need to interleave the commands to do that so that stepper1 moves a step, then stepper2 moves a step, then stepper1 moves a step and so on.



The library provides a way to do that:



```python

s1 = Stepper(HALF_STEP, microbit.pin16, microbit.pin15, microbit.pin14, microbit.pin13, delay=5)    

s2 = Stepper(HALF_STEP, microbit.pin6, microbit.pin5, microbit.pin4, microbit.pin3, delay=5)   



c1 = Command(s1, FULL_ROTATION)         # Go all the way round

c2 = Command(s2, FULL_ROTATION/2, -1)   # Go halfway round, backwards



runner = Driver()

runner.run([c1, c2])

```



The Driver class will run 1 step from each command until there are no more commands to run which will make the two motors move (apparently) simultaneously.