Arduino 7-segment display driver

arduino-7seg.cc

namespace {

const char segment_pin[7] = {
  [0] = 0,
  [1] = 0,
  [2] = 0,
  [3] = 0,
  [4] = 0,
  [5] = 0,
  [6] = 0,
};

constexpr int hassomething(char c) {
  if (c == ' ')
    return 0;
  return 1;
}

constexpr unsigned char SegmentToFontData(const char *drawing) {
  /*
   * This function calculates which segments will light up according to a
   * diagram of a 7-segment display:
   *
   * +------------ 5
   * |  +--------- 0
   * |  v
   * |  _
   * +>|_| <------ 1        (6 is the middle segment)
   * +>|_| <------ 2
   * |  ^
   * |  +--------- 3
   * +------------ 4
   */
     
  unsigned char data = 0;

  data  = hassomething(drawing[1]);
  data |= 1<<(1 * hassomething(drawing[5]));
  data |= 1<<(2 * hassomething(drawing[8]));
  data |= 1<<(3 * hassomething(drawing[7]));
  data |= 1<<(4 * hassomething(drawing[6]));
  data |= 1<<(5 * hassomething(drawing[3]));
  data |= 1<<(6 * hassomething(drawing[4]));

  return data;
}


const char font[] = {
  [0] = SegmentToFontData(
        " _ "
        "| |"
        "|_|"),
  [1] = SegmentToFontData(
        "   "
        "  |"
        "  |"),
  [2] = SegmentToFontData(
        " _ "
        " _|"
        "|_ "),
  [3] = SegmentToFontData(
        " _ "
        " _|"
        " _|"),
  [4] = SegmentToFontData(
        "   "
        "|_|"
        "  |"),
  [5] = SegmentToFontData(
        " _ "
        "|_ "
        " _|"),
  [6] = SegmentToFontData(
        " _ "
        "|_ "
        "|_|"),
  [7] = SegmentToFontData(
        " _ "
        "  |"
        "  |"),
  [8] = SegmentToFontData(
        " _ "
        "|_|"
        "|_|"),
  [9] = SegmentToFontData(
        " _ "
        "|_|"
        " _|"),
};

};

class DisplayDigit {
 private:
  int anode_pin_;
 public:
  DisplayDigit(int anode_pin) : anode_pin_(anode_pin) {}
  void Deactivate();
  void DisplayNumber(int number);
};

void DisplayDigit::Deactivate() {
  digitalWrite(anode_pin_, LOW);
}

void DisplayDigit::DisplayNumber(int number) {
  for (int segment = 0; segment < 7; segment++)
    digitalWrite(segment_pin[segment], font[number] & 1<<segment);
  digitalWrite(anode_pin_, HIGH);
}

class Display {
 private:
  DisplayDigit *digits_;
  int n_digits_;
  int number_;
 public:
  ~Display();
  
  void Init(int n_digits);

  void DisplayNumber(int number);
  void Loop();
};

void Display::Init(int n_digits) {
  n_digits_ = n_digits;
  digits_ = new DisplayDigit[n_digits];
}

Display::~Display() {
  delete[] digits_;
}

void Display::DisplayNumber(int number) {
  number_ = number;
}

void Display::Loop() {
  int number, digit;
  for (number = number_, digit = n_digits_;
          number && digit; number /= 10, digit--) {
    if (digit != n_digits_)
      digits_[digit + 1]->Deactivate();
    digits_[digit]->DisplayNumber(number % 10);
  }
  for (; digit; digit--)
    digits_[digit]->Deactivate();
}

Display d;

void setup() {
  d.Init(7);
  d.DisplayNumber(42);
}

void loop() {
  d.Loop();  
}