Module.h

#include <Arduino.h>

class Module {
public:

  // Public vars
  int motorPins[4];
  bool homing;
  char displayed;
  bool moving;

  // Module constructor
  Module() {

    // CONSTANTS
    flapsCount = 40; // Flaps in module
    stepsPerRev = 2048; // Steps per motor full revolution
    stepsPerFlap = stepsPerRev / flapsCount; // Steps required to rotate one character forward
    stepInterval = 1700; // Time interval between each motor step in microseconds

    // VARS
    stepSequenceIdx = 0;
    flapStepIdx = 0;
    lastStepTime = 0;
    displayedIdx = 0;
    moving = false;
    offsetSteps = 0;
  }

  void setup(int hallPin, int in1, int in2, int in3, int in4, int off) {

    offset = off;

    // Rearrange stepper pins in order IN1-IN3-IN2-IN4
    motorPins[0] = in1;
    motorPins[1] = in3;
    motorPins[2] = in2;
    motorPins[3] = in4;

    // Set all stepper pins as outputs
    for (int i = 0; i < 4; i++) pinMode(motorPins[i], OUTPUT);

    sensorPin = hallPin;
    pinMode(sensorPin, INPUT_PULLUP);  // Set hall effect sensor pin as an input with pullup resistor
  }

  void tick() {

    if (homing) {
      // If module is already on magnet before homing, rotate until not on magnet
      if (preHoming) {
        if (step() && !isOnMagnet()) {
          preHoming = false;
        }
        return;
      }
      // Offset
      if (offsetSteps) {
        if (step()) {
          offsetSteps--;
          if (!offsetSteps) {
            setHome(); // stop homing sequence
            turnOffInputs();
          }
        }
        return;
      }
      // Try to step and check if home position is reached
      if (step() && isOnMagnet()) {
        if (offset) {
          offsetSteps = offset;
        } else {
          setHome(); // stop homing sequence
          turnOffInputs();
        }
      }
      return; // Finish homing before rotating to target character
    }

    // Step until target character has been reached
    if (moving && step() && displayedIdx == targetIdx) {
      moving = false;
      turnOffInputs();
    }
    
  }
  
  void home() {
    preHoming = true;
    homing = true;
  }

  void display(char c) {

    c = toupper(c);
    if (targetIdx == findCharIdx(c)) return;
    targetIdx = findCharIdx(c);

    // Loop back to home if target character is behind currently displayed
    if (targetIdx < displayedIdx) {
      home();
    }
    if (targetIdx != displayedIdx) {
      moving = true;
    }
    
  }

private:
  int sensorPin;
  int flapsCount;
  int stepsPerRev;
  int stepsPerFlap;
  int stepInterval;
  int stepSequenceIdx;
  int flapStepIdx;
  int displayedIdx;
  int targetIdx;
  int offset;
  int offsetSteps;
  unsigned long lastStepTime;
  bool preHoming;
  bool stepSequence[4][4] = {
    { 1, 0, 0, 1 },
    { 0, 1, 0, 1 },
    { 0, 1, 1, 0 },
    { 1, 0, 1, 0 }
  };
  char chars[40] = { ' ', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', ':', '$' };

  void setHome() {
    displayedIdx = 0;
    displayed = chars[0];
    flapStepIdx = 0;
    homing = false;
  }

  bool step() {
    unsigned long now = micros();
    if (now - lastStepTime < stepInterval) return false;
  
    // Write correct sequence to step the motor
    for (int in = 0; in < 4; in++) digitalWrite(motorPins[in], stepSequence[stepSequenceIdx][in]);

    // Next in sequence
    stepSequenceIdx++;
    if (stepSequenceIdx == 4) {
      stepSequenceIdx = 0;
    }

    // flap step
    flapStepIdx++;
    if (flapStepIdx == stepsPerFlap) {
      flapStepIdx = 0;
      displayedIdx++;
      if (displayedIdx == flapsCount) {
        displayedIdx = 0;
      }
      displayed = chars[displayedIdx];
    }
    
    lastStepTime = now;
    return true;
  }

  void turnOffInputs() {
    for (int in = 0; in < 4; in++) {
      digitalWrite(motorPins[in], LOW);
    }
  }

  bool isOnMagnet() {
    return !digitalRead(sensorPin);
  }

  int findCharIdx(char c) {
    for (int i = 0; i < flapsCount; i++) if (chars[i] == c) return i;
    return -1;
  }

};