What is the easiest way to drive a Bipolar Stepper Motor? PWM, PPI, direct output pin control?

[EricDelangis]

I've reviewed the different PWM examples that include the low power PWM, PWM driver and the PWM library.  What I'm looking for is a very simple solution to drive a bipolar stepper motor using two pins that control a stepper motor driver IC.  To drive a bipolar stepper motor all I need to do is to send four values {00, 10, 11, 01} on the two pins for one direction and in reverse order for the opposite direction.  I want to be able to control the number of steps that the the stepper rotates as well as to have it run for a period of time until I turn it off.  I also want to control the speed of the steps.  I'm not sure that the PWM is the best way to do this.  I've also determined that the low power PWM solution is adequate for my application, if using the PWM function is the best way to implement this, in that I don't need a high frequency for the stepper motor. 

Please advise.

[Sigurd]

Hi,

To drive a bipolar stepper motor all I need to do is to send four values {00, 10, 11, 01} on the two pins for one direction and in reverse order for the opposite direction. 

So for 00, both pins are low? and for 11 both pins are high ?

How often are these values supposed to change (what frequency) ? 

I want to be able to control the number of steps that the the stepper rotates

 How does this correlate to the four values ? 00 is one step, 10 is another step ?

Do you have datasheet for this motor?

[EricDelangis]

The two motor control signals control a motor driver circuit L6225 that creates a differential pair of drive signals for each of the two different coils in the bipolar stepper motor.  So, my two control signals become 4 drive signals to power the stepper motor. I've attached the datasheet.  Stepper motor drawing (Kevins)-revised- Final Approved.pdf 

To answer your questions, my step frequency will be less than (i.e. slower than) one step per 10mS.  So the frequency is very low.  And yes, 00, 10, 11, 01 are the four steps required to step the motor 4 steps.  This sequence repeats to continue stepping in one direction.  To reverse direction these steps are performed in the reverse order.  Putting 00 on the two step control pins followed by a 10 will cause the motor to move one step.  Then changing the control pins from 10 to 11 will cause it to step once more.  Changing from 11 to 01 is another step and then 00 is the fourth step.  And from here the sequence repeats.

Since I submitted this support request, I've studied the nRF52832 datasheet and have come to the conclusion that using the GPIO library seems to be the best solution since it gives me the ability to control the number of steps that I want the stepper to make at any given time, as well as to reverse direction at will.  I don't see a good option using the PWM output to be able to accurately control the number of steps.  The PPI subsection is soooo complicated and the documentation is rather thin considering it's complexity that I don't see a clean way to use it.  Maybe PPI is a good solution but I don't understand how to apply it.

[Sigurd]

EricDelangis said:

And yes, 00, 10, 11, 01 are the four steps required to step the motor 4 steps.  This sequence repeats to continue stepping in one direction.  To reverse direction these steps are performed in the reverse order.  Putting 00 on the two step control pins followed by a 10 will cause the motor to move one step.  Then changing the control pins from 10 to 11 will cause it to step once more.  Changing from 11 to 01 is another step and then 00 is the fourth step.  And from here the sequence repeats.

 I would try using PWM for this first.

Here is an example on how to achieve this "00, 10, 11, 01" sequence, with 10ms steps on pin 3 and 27:

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/** @file
 * @defgroup pwm_example_main main.c
 * @{
 * @ingroup pwm_example
 *
 * @brief PWM Example Application main file.
 *
 * This file contains the source code for a sample application using PWM.
 */

#include <stdio.h>
#include <string.h>
#include "nrf_drv_pwm.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"
#include "bsp.h"
#include "app_timer.h"
#include "nrf_drv_clock.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

#define PWM_PIN_0 3
#define PWM_PIN_1 27


#define HIGH 0x8000
#define LOW 0x0




static void pwm_init(void)
{
    nrf_drv_pwm_config_t config =
    {
        // These are the common configuration options we use for all PWM
        // instances.
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .count_mode   = NRF_PWM_MODE_UP,
        .step_mode    = NRF_PWM_STEP_AUTO,
    };

    config.base_clock = NRF_PWM_CLK_125kHz;
    config.top_value  = 1250;
    config.load_mode  = NRF_PWM_LOAD_INDIVIDUAL;


    config.output_pins[0] = PWM_PIN_0 | NRF_DRV_PWM_PIN_INVERTED;
    config.output_pins[1] = PWM_PIN_1 | NRF_DRV_PWM_PIN_INVERTED;
    config.output_pins[2] = NRF_DRV_PWM_PIN_NOT_USED;
    config.output_pins[3] = NRF_DRV_PWM_PIN_NOT_USED;
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config, NULL));
}

static void start_pwm_demo()
{
    // Sequence 0:
    static nrf_pwm_values_individual_t seq0_values[] =
    {
        { LOW,   LOW,  0,0 },
        { HIGH,  LOW,  0,0 },
        { HIGH,  HIGH, 0,0 },
        { LOW,   HIGH, 0,0 }


    };

    nrf_pwm_sequence_t const pwm0_seq0 =
    {
        .values.p_individual = seq0_values,    
        .length          = NRF_PWM_VALUES_LENGTH(seq0_values),
        .repeats         = 0,
        .end_delay       = 0
    };



    (void)nrf_drv_pwm_simple_playback(&m_pwm0, &pwm0_seq0, 1,
                                       NRF_DRV_PWM_FLAG_LOOP);


}



static void bsp_evt_handler(bsp_event_t evt)
{

    switch (evt)
    {
        case BSP_EVENT_KEY_0:
             //start_pwm_demo();
             break;
            
        default:
            return;
    }

}



void app_error_fault_handler(uint32_t id, uint32_t pc, uint32_t info)
{
    bsp_board_leds_on();
    app_error_save_and_stop(id, pc, info);
}

static void init_bsp()
{
    APP_ERROR_CHECK(nrf_drv_clock_init());
    nrf_drv_clock_lfclk_request(NULL);

    APP_ERROR_CHECK(app_timer_init());
    APP_ERROR_CHECK(bsp_init(BSP_INIT_BUTTONS, bsp_evt_handler));
    APP_ERROR_CHECK(bsp_buttons_enable());
}


int main(void)
{
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();


    NRF_LOG_INFO("PWM example started.");
    init_bsp();

    bool accurate_HFCLK = true;

    if(accurate_HFCLK)
    {
      // Start accurate HFCLK (XOSC)
      NRF_CLOCK->TASKS_HFCLKSTART = 1;
      while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
      NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    }

    pwm_init();
    start_pwm_demo();

    for (;;)
    {
        // Wait for an event.
        __WFE();

        // Clear the event register.
        __SEV();
        __WFE();

        NRF_LOG_FLUSH();
    }
}


/** @} */

Replace the code in the pwm_driver example in the SDK, with the code above to test it.