MCP23017 I2C AccelStepper library for Arduino

Extension for the AccelStepper library.

With this library AccelStepper can be used to control steppers using a MCP23017 I/O Expander over I2C interface. This requires only two pins to be used A4 SDA and A5 SCL on the Arduino Uno. MCP23017AccelStepper extends AccelStepper which means that all the functionality of AccelStepper is still there.

• I2C support using a MCP23017 I/O Expander.
• When used with the driver interface the third pin for the constructor can be used to set the enable pin.
• By not calling setMcp it will fallback to the Arduino pins.

Example

#include <Wire.h>
#include <Adafruit_MCP23017.h>
#include <AccelStepper.h>
#include <MCP3017AccelStepper.h>

#define STEPPER_COUNT 4

Adafruit_MCP23017 mcp1;

MCP3017AccelStepper steppers[STEPPER_COUNT] = {
    // interface, step, dir, en
    MCP3017AccelStepper(AccelStepper::DRIVER, 15, 14, 8),
    MCP3017AccelStepper(AccelStepper::DRIVER, 4, 5, 6),
    MCP3017AccelStepper(AccelStepper::DRIVER, 12, 11, 10),
    MCP3017AccelStepper(AccelStepper::DRIVER, 3, 1, 2),
};

void setup() {
  mcp1.begin();

  for (int i = 0; i < STEPPER_COUNT; i++) {
    steppers[i].setMcp(mcp1);
    steppers[i].enableOutputs();
    steppers[i].setMaxSpeed(150.0);
    steppers[i].setAcceleration(100.0);
    steppers[i].moveTo(200);
  }
}

void loop() {
  if (steppers[0].distanceToGo() == 0) {
    steppers[0].moveTo(-steppers[0].currentPosition());
  }

  for (int i = 0; i < STEPPER_COUNT; i++) {
    steppers[i].run();
  }
}

Making things run smooth

Ones you have a couple of steppers running you might notice that they're a bit slow. To make them run smooth you can change the clock frequency of the I2C bus. More on this here http://playground.arduino.cc/Code/ATMELTWI#line7

mcp1.begin();
TWBR = 12;  // 400 kHz 
// TWBR = 72;  // 100 kHz (default)

Dependencies

External dependencies, the Wire library is also needed but is bundled with the Arduino software.

• AccelStepper
  • Private methods of the AccelStepper library must be modified to be protected.
• Adafruit MCP23017

License

GPL V2, same as AccelStepper http://www.airspayce.com/mikem/arduino/AccelStepper/

Author

2013 Johan Nilsson http://www.markupartist.com