Using PWM to step a stepper driver

[dinther]

Thank you for making your RP2040_PWM library available. It was super easy to use. Yesterday I tried using it to drive a single stepper motor with it using a STEP/DIR style stepper driver. A TMC2209 in my case. It worked perfectly at first try.

I discussed the details with the author of arduinocontinuousstepper to hear his take on it and he thinks it has merit.

However, looking ahead there might be an issue when multiple motors are used. From what I understand from your RP2040_PWM project is that we can have 8 independent PWM frequencies but will they all run in sync.

So my question is: Are all these frequencies derived from a common clock or is there a way to achieve synchronization between PWM channels?

[edit]

Since I posted this I came across a video explaining the pico pwm in laymans terms. From it I understand that each PWM channel is basically a hardware based counter counting pulses from a common125MHz clock using their own setpoint and wrappoint. That confirms to me that yes there is a common clock and my motors will be perfectly in sync.

But please correct me if I am wrong :-)

[khoih-prog]

Hi @dinther

I'm glad that you find out a new way to drive the stepper-motor driver using PWM, instead of using conventional Timers, etc.
The fully-hardware PIO PWM of cheap-yet-powerful RP2040 is perfect for this purpose to offload the MPU for other purposes.

You can read The RP2040's PWM excellence to appreciate RP2040 PWM if you'd like to use for more complex purpose (phase-shift PWM, etc.)

there is a common clock and my motors will be perfectly in sync.

I believe you're correct.

Best Regards,

[khoih-prog]

Hi @dinther

Just have an idea from you novel implementation using PWM for Stepper-Motor control, which is better solution than using Timers.

As I have many PWM-related libraries, can you make PRs to add the similar examples controlling Stepper to those libraries, as I don't have the motor as well as driver (such as TMC2209) to test.

Please inform if you're OK

Best,

[dinther]

I have not checked your source yet but I have been assuming that the RP2040 uses PIO for PWM because PIO can also offer up to 8 independent channels. Same limit as PWM other limitations match PIO limitations as well. You are absolutely correct that the PIO is just ideal for this from what I read and watched in PIO for beginners videos. I am way out of my depth on all this as I don't have the expertise you have.

I will have to dig deeper but a stepper library making use of PIO is the right way to go about it. I definitely avoid timers.

This code below using your library worked although after a while I noticed irregularities in the running of the motor. I have not examined that yet. I'' put it on the oscilloscope sometime this week.

// Use with Stepper-Motor driver, such as TMC2209

#define _PWM_LOGLEVEL_        1

#if ( defined(ARDUINO_NANO_RP2040_CONNECT) || defined(ARDUINO_RASPBERRY_PI_PICO) || defined(ARDUINO_ADAFRUIT_FEATHER_RP2040) || \
      defined(ARDUINO_GENERIC_RP2040) ) && defined(ARDUINO_ARCH_MBED)

  #if(_PWM_LOGLEVEL_>3)
    #warning USING_MBED_RP2040_PWM
  #endif

#elif ( defined(ARDUINO_ARCH_RP2040) || defined(ARDUINO_RASPBERRY_PI_PICO) || defined(ARDUINO_ADAFRUIT_FEATHER_RP2040) || \
        defined(ARDUINO_GENERIC_RP2040) ) && !defined(ARDUINO_ARCH_MBED)

  #if(_PWM_LOGLEVEL_>3)
    #warning USING_RP2040_PWM
  #endif
#else
  #error This code is intended to run on the RP2040 mbed_nano, mbed_rp2040 or arduino-pico platform! Please check your Tools->Board setting.
#endif

#include <RP2040_PWM.h>

RP2040_PWM* stepper;

#define STEP_PIN      8
#define DIR_PIN       9

void setSpeed(int speed)
{
  if (speed == 0)
  {
    // Use DC = 0 to stop stepper
    stepper->setPWM(STEP_PIN, 500, 0);
  }
  else
  {
    //  Set the frequency of the PWM output and a duty cycle of 50%
    digitalWrite(DIR_PIN, (speed < 0));
    stepper->setPWM(STEP_PIN, abs(speed), 50);
  }
}

void setup() 
{
  pinMode(DIR_PIN, OUTPUT);
  
  Serial.begin(115200);

  while (!Serial && millis() < 5000);

  delay(100);

  Serial.print(F("\nStarting PWM_StepperControl on "));
  Serial.println(BOARD_NAME);
  Serial.println(RP2040_PWM_VERSION);
  
  // Create PWM object and passed just a random frequency of 500
  // The duty cycle is how you turn the motor on and off
  stepper = new RP2040_PWM(STEP_PIN, 500, 0);
}

void loop() 
{
  setSpeed(1000);
  delay(3000);

  // Stop before reversing
  setSpeed(0);
  delay(3000);

  // Reversing
  setSpeed(-500);
  delay(3000);

  // Stop before reversing
  setSpeed(0);
  delay(3000);
}

[khoih-prog]

Hi @dinther

Just add the example PWM_StepperControl, with your credit notes.

RP2040_PWM/examples/PWM_StepperControl/PWM_StepperControl.ino

Line 13 in b3d063a

Credits of Paul van Dinther (https://github.com/dinther). Check https://github.com/khoih-prog/RP2040_PWM/issues/16

Please check, test and report / fix errors

Best,

[khoih-prog]

Please try this if OK, with stepper stops before reversing

// Use with Stepper-Motor driver, such as TMC2209

#define _PWM_LOGLEVEL_        1

#if ( defined(ARDUINO_NANO_RP2040_CONNECT) || defined(ARDUINO_RASPBERRY_PI_PICO) || defined(ARDUINO_ADAFRUIT_FEATHER_RP2040) || \
      defined(ARDUINO_GENERIC_RP2040) ) && defined(ARDUINO_ARCH_MBED)

  #if(_PWM_LOGLEVEL_>3)
    #warning USING_MBED_RP2040_PWM
  #endif

#elif ( defined(ARDUINO_ARCH_RP2040) || defined(ARDUINO_RASPBERRY_PI_PICO) || defined(ARDUINO_ADAFRUIT_FEATHER_RP2040) || \
        defined(ARDUINO_GENERIC_RP2040) ) && !defined(ARDUINO_ARCH_MBED)

  #if(_PWM_LOGLEVEL_>3)
    #warning USING_RP2040_PWM
  #endif
#else
  #error This code is intended to run on the RP2040 mbed_nano, mbed_rp2040 or arduino-pico platform! Please check your Tools->Board setting.
#endif

#include <RP2040_PWM.h>

RP2040_PWM* stepper;
float frequency;
float dutyCycle;
#define STEP_PIN      8
#define DIR_PIN       9

void setSpeed(int speed)
{
  if (speed == 0)
  {
    // Use DC = 0 to stop stepper
    stepper->setPWM(STEP_PIN, 500, 0);
  }
  else
  {
    //  Set the frequency of the PWM output and a duty cycle of 50%
    digitalWrite(DIR_PIN, (speed < 0));
    stepper->setPWM(STEP_PIN, abs(speed), 50);
  }
}

void setup() 
{
  pinMode(DIR_PIN, OUTPUT);
  
  Serial.begin(115200);

  while (!Serial && millis() < 5000);

  delay(100);

  Serial.print(F("\nStarting PWM_StepperControl on "));
  Serial.println(BOARD_NAME);
  Serial.println(RP2040_PWM_VERSION);
  
  //  Create PWM object and passed just a random frequency of 500 in it
  //  The duty cycle is how you turn the motor on and off
  stepper = new RP2040_PWM(STEP_PIN, 500, 0);
}

void loop() 
{
  setSpeed(1000);
  delay(3000);
  setSpeed(0);
  delay(3000);
  setSpeed(-500);
  delay(3000);
}