Step-direction interface

Step/direction communication is one of the most common communication interface for running stepper motors. It is very basic, it uses two digital signals, step and direction. step signal produces and short impulse which signals that the motor should do a step with predefined length and direction signal determines the direction of the movement (ex. HIGH forward, LOW backward).

As stated before this interface is particularly well suited for stepper motors because their motion is designed to be characterised by steps. But this interface can be used in many different ways that have nothing to do with stepper motors. In general step/dir interface can be described as a counter where direction signal determines the counting direction and step provides the impulses to be counted:

// on rising edge of step signal 
if(direction == HIGH) counter++;
else counter--; 

Finally to obtain the value you are interested in you just need to multiplied the current counter value with your step value:

received_value = counter*my_step;

How to use Step-direction listener

In order to do this in a more concise manner SimpleFOClibrary implements an interrupt based version of this interface based on the StepDirListener class:

// StepDirListener(step, dir, counter_to_value)
// - step              - step pin number
// - dir               - dir pin number
// - step_per_rotation - transformation variable from step count to your variable (ex. motor angle in radians)
StepDirListener step_dir = StepDirListener( 2, 5, _2PI/200.0 );

Once the StepDirListener class has been defined its hardware pins will be configured in the init() funciton which needs to be added to the setup() function.

// init step and dir pins
step_dir.init();

Furthermore, in order to do the actual counting this library uses the interrupt based approach, therefore the StepDirListener provides you the handle() function that you just need to wrap for example:

// static wrapper function
void onStep() { step_dir.handle(); }

and finally you can enable the counter by providing the wrapper function to the enableInterrupt() function:

// enable interrupts 
step_dir.enableInterrupt(onStep);

Finally, the user has two ways to get the received value. It can be read by calling the getValue() function:

float my_variable = step_dir.getValue();

The second way to get the value is to attach the variable you wish the StepDirListener updates each time it updates the counter:

// some variable user wants to update 
float my_value;
// attach the variable to be updated on each step (optional) 
step_dir.attach(&my_value);

⚠️ BEWARE: Suboptimal performance

The simplest forms of communication such as step/dir are designed to be handled in hardware and software, interrupt based, implementation of these communication interfaces is usually not the optimal solution. It will provide the user a good base for testing purposes, but it is hard to guarantee long-term robustness.

Example code

This is a simple code of step-dir listener. See more examples in library examples examples/utils/communication_test/step_dir folder.

/**
 * A simple example of reading step/dir communication 
 *  - this example uses interrupts
*/

#include <SimpleFOC.h>

// angle 
float received_angle = 0;

// StepDirListener( step_pin, dir_pin, counter_to_value)
StepDirListener step_dir = StepDirListener(2, 3, 360.0/200.0); // receive the angle in degrees
void onStep() { step_dir.handle(); }

void setup() {

  Serial.begin(115200);
  
  // init step and dir pins
  step_dir.init();
  // enable interrupts 
  step_dir.enableInterrupt(onStep);
  // attach the variable to be updated on each step (optional) 
  // the same can be done asynchronously by caling step_dir.getValue();
  step_dir.attach(&received_angle);
    
  Serial.println(F("Step/Dir listenning."));
  _delay(1000);
}

void loop() {
  Serial.print(received_angle);   // automatically updated by the StepDirListener class
  Serial.print("\t");
  Serial.println(step_dir.getValue()); // getter of the StepDirListener class
  _delay(500);
}