stepping-razor

MicroPython class for unipolar stepper motors such as 28BYJ-48. Also a classic tune by Peter Tosh.

I was experimenting with a 28BYJ-48 stepper motor driven by a ULN2003 connected to an ESP32-C3 OLED. Found no existing module that I liked, so I made this one. Maybe it will help someone else.

The main feature, compared to other ULN2003-modules, is that this module considers the current step position (active coils) before taking a new step. Thus, not trying to move the rotor more than one position at a time.

Default is full drive stepping, for more power. Wave drive is also supported. Drive type is determined by first_step when instantiating the class.

• Wave drive: The four coils take turn being active one at a time, such as [1,0,0,0] to [0,1,0,0] to [0,0,1,0] to [0,0,0,1] to [1,0,0,0] and so on. Or the reverse order for counter-clockwise.
• Full drive: The four coils take turn being active two at a time, such as [1,1,0,0] to [0,1,1,0] to [0,0,1,1] to [1,0,0,1] to [1,1,0,0] and so on. Or the reverse order for counter-clockwise.

Installation

1. Upload steppingrazor.py to your ESP32 or similar MicroPython device.
2. In your MicroPython device, run import-module steppingrazor

Instantiation of class steppingrazor.uln2003() as "my_stepper"

Basic: my_stepper = steppingrazor.uln2003(0, 1, 2, 21) where the four INT's are your four pins going to IN ports on the ULN2003. 0,1,2,21 is just a convenient example of pins on an ESP32-C3 OLED version.

Advanced: my_stepper = steppingrazor.uln2003(in1=0, in2=1, in3=2, in4=21, first_step=[0,1,1,0], steps_per_rev=2048.0, delay_ms=3) where

• in1...in4 are the numbers of four pins going to IN ports on the ULN2003. N.b! Just the pin numbers, not machine.Pin().
• first_step is the step configuration, i.e. active coils to start with. Full/Wave drive is determined by the pattern of 0/1 in this list.
• steps_per_rev is how many steps the motor needs to rotate 360 degrees
• delay_ms is the delay after taking a step. Anti-proportional to speed. The rotor needs some time to move after each re-configuration of active coil(s).

Functions on "my_stepper" object

my_stepper.rotate_deg()

Rotate an angle in degrees. Can be less than 0 and more than 360.

my_stepper.position_deg()

Get/set position to a number of degrees from home. Can be less than 0 and more than 360.

• Get: my_stepper.position_deg()
• Set: my_stepper.position_deg(600)

my_stepper.rotate_steps()

Rotate a number of steps. Can be under 0 and over steps_per_rev.

my_stepper.position_steps()

Get/set position to a number of steps from home. Can be under 0 and over steps_per_rev.

• Get: my_stepper.position_steps().
• Set: my_stepper.position_steps(3000).

my_stepper.step_once()

Take a single step

• clockwise: my_stepper.step_once(1) Any INT between 1 and infinity = 1 step clockwise.
• counter clockwise: my_stepper.step_once(-1) Any INT between -1 and -infinity = 1 step counter clockwise.

my_stepper.set_home()

Set home at current position/step.

my_stepper.set_coils()

Activate the four coils according to a list.

After instantiating my_stepper, no coils are active - i.e. the shaft can move freely until a step is set. This way, you can store the last step (=position) to non-volatile storage, and then at boot set_coils() to the last known position of the shaft. Example usages to set coils to...

• class default list: my_stepper.set_coils()
• first position: my_stepper.set_coils([1,1,0,0])
• free rotation: my_stepper.set_coils([0,0,0,0])

If your'e not worried about precise decimal degrees, just forget about this function, and use rotate_*() or, position_*() described above.

my_stepper.step_count()

Get/set step counter INT to answer the question "where am I?". Mostly for internal use.

my_stepper.invert_rotation()

Get/set inversion of rotation. Useful since "clockwise" may mean different things in different setups.

• Get: my_stepper.invert_rotation()
• Set: my_stepper.invert_rotation(True) or False

my_stepper.delay_ms()

Get/set milliseconds delay between steps to control speed vs torque.

• Get: my_stepper.delay_ms()
• Set: my_stepper.delay_ms(10)

my_stepper.steps_per_revolution()

Get/set how many steps the motor takes forone full revolution (360deg).

• Get: my_stepper.steps_per_revolution()
• Set: my_stepper.steps_per_revolution(2048) Standard 28BYJ-48

my_stepper.get_drive_type()

Get drive type, wave or full depending on first_step list.