pico-stepper

A C library for using a stepper motor with the Raspberry Pi Pico

Works with 4-wire bipolar or unipolar stepper motors. Two stepping modes have so far been implemented: "single" and "power" (see below).

Wiring

Driving a stepper motor with the Pico (or pretty much any other microcontroller) requires a driver circuit, typically one H-bridge for each coil pair. There are many dual H-bridge motor driver breakout boards readily available (e.g. Adafruit #2448) and using one of these is an easy way to connect a stepper motor to a Pico.

Connect the stepper motor to the dual H-bridges board as per the board's instructions. Then connect the motor board to the Pico so that four of the Pico's GPIOs are used to control motor rotation.

Software

1. Download this pico-stepper library.

2. Create a Pico project. Edit CMakeLists.txt in your project to include the path to the pico-stepper library. E.g. if the pico-stepper library is located one directory above (../) your project then your CMakeLists.txt file should include these lines:

.
.
.
include(pico_sdk_import.cmake)
add_subdirectory(../pico-stepper/lib stepper)

target_link_libraries(<name-of-your-project>
        pico_stdlib
        pico-stepper
)
.
.
.

3. Include the stepper library in your project and use as in e.g. (see the examples directory for full working code):

.
.
.
#include "stepper.h"

stepper_t stepper;
const uint8_t stepper_pin_1A = 12;  // NOTE [1]
const uint8_t stepper_pin_1B = 13;
const uint8_t stepper_pin_2A = 14;
const uint8_t stepper_pin_2B = 15;
const uint16_t stepper_steps_per_revolution = 200;  // NOTE [2]
const stepper_mode_t stepping_mode = single;  // NOTE [3]

int main() {
    stdio_init_all();
    stepper_init(&stepper, stepper_pin_1A, stepper_pin_1B,
                 stepper_pin_2A, stepper_pin_2B,
                 stepper_steps_per_revolution, stepping_mode);
    stepper_set_speed_rpm(&stepper, 20);  // NOTE [4]

    while (true) {
        stepper_rotate_steps(&stepper, 200);  // NOTE [5]
        sleep_ms(1000);
        stepper_rotate_degrees(&stepper, -90);
        sleep_ms(1000);
    }
    return 0;
}

4. Compile your project and run.

Notes

[1] These are the four GPIOs that will control each of the coils in the stepper. The number indicates a coil pair; i.e. in the example above GPIOs 12 and 13 will control the first coil pair (stepper_pin_1x), and GPIOs 14 and 15 will control the second coil pair (stepper_pin_2x).

[2] These are the number of steps needed for the motor to fully rotate once. This value depends on the specific motor used.

[3] Stepping mode can be single or power, and refers to the firing sequences used to step the motor: in single mode one coil is active at any one time, whereas in power mode two coils are powered at once. power stepping provides more torque than single stepping but uses more power (Scherz and Monk, 2013). Also, in power mode the motor turns more smoothly but it does get considerably hotter.

[4] This sets the rotation speed, in revolutions per minute (RPM).

[5] This function rotates the motor these many steps. If the number of steps is negative, the motor rotates in the oposite direction.

References

Scherz and Monk (2013). "Practical Electronics for Inventors" 3rd Ed., McGraw-Hill, 2013. (Sections 14.5 to 14.9 are a very useful introduction to stepper motors.)