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.
You will need:
- A micro:bit with USB cable (and a computer to connect it to!)
- A 5V DC power source
- One or more 28BYJ-48 stepper motors with matching ULN2003 driver boards
- Wires, lots of wires.
- (Optional but handy) A breakout board to make accessing the bit's IO pins easier
Wiring / Connecting
- Plug the stepper motor into the ULN2003
- Connect the 4 pins from the ULN2003 into 4 separate I/O pins of the bit
- Connect the 5v input +/- on the ULN2003 to a 5v source +/- terminals
- Connect the bit to the computer
- Load up the library and push to the bit (i.e. compile the program and upload to the bit)
Using the library
# 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:
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:
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.