/*
  Driving multiple 7-seg displays with 74HC595 shift registers.
  
  Feel free to re-use.
  
   01/30/2010
*/

// This pin gets sets low when I want the 595s to listen
const int  g_pinCommLatch = 6;

// This pin is used by ShiftOut to toggle to say there's another bit to shift
const int  g_pinClock     = 7;

// This pin is used to pass the next bit
const int  g_pinData    = 4;

// Definitions of the 7-bit values for displaying digits
byte g_digits [10];

// Current number being displayed
int g_numberToDisplay = 0;

// Number of shift registers in use
const int g_registers = 4;

// Array of numbers to pass to shift registers
byte g_registerArray [g_registers];

void setup()
{
  pinMode (g_pinCommLatch, OUTPUT);
  pinMode (g_pinClock, OUTPUT);
  pinMode (g_pinData, OUTPUT);
  
  Serial.begin (56600);
  
  // Setup the digits array
  // a = 8 b = 4 c = 2 d = 64 e = 32 f = 1 g = 16
  g_digits [0] = 8 + 4 + 2 + 64 + 32 + 1;
  g_digits [1] = 4 + 2;
  g_digits [2] = 8 + 4 + 16 + 32 + 64;
  g_digits [3] = 8 + 4 + 16 + 2 + 64;
  g_digits [4] = 1 + 16 + 4 + 2;
  g_digits [5] = 8 + 1 + 16 + 2 + 64;
  g_digits [6] = 8 + 1 + 16 + 2 + 64 + 32;
  g_digits [7] = 8 + 4 + 2;
  g_digits [8] = 8 + 4 + 2 + 64 + 32 + 1 + 16;
  g_digits [9] = 8 + 4 + 2 + 1 + 16 + 64;
} // setup

// Simple function to send serial data to one or more shift registers by iterating backwards through an array.
// Although g_registers exists, they may not all be being used, hence the input parameter.
void sendSerialData (
  byte registerCount,  // How many shift registers?
  byte *pValueArray)   // Array of bytes with LSByte in array [0]
{
  // Signal to the 595s to listen for data
  digitalWrite (g_pinCommLatch, LOW);
  
  for (byte reg = registerCount; reg > 0; reg--)
  {
    byte value = pValueArray [reg - 1];
    
    for (byte bitMask = 128; bitMask > 0; bitMask >>= 1)
    {
      digitalWrite (g_pinClock, LOW);
    
      digitalWrite (g_pinData, value & bitMask ? HIGH : LOW);
        
      digitalWrite (g_pinClock, HIGH);
    }
  }
  // Signal to the 595s that I'm done sending
  digitalWrite (g_pinCommLatch, HIGH);
}  // sendSerialData

// Print a message specifying valid inputs, given the number of registers defined and then consume all current input.
void badNumber ()
{
  int dummy;
  
  Serial.print ("Please enter a number from 0 to ");
  for (int loop = 0; loop < g_registers; loop++)
  {
    Serial.print ("9");
  }
  Serial.println (" inclusive.");
  
  while (Serial.available () > 0)
  {
    dummy = Serial.read ();
    
    // Necessary to get all input in one go.
    delay (10);
  }
} //badNumber

// Read a number from the PC with no more digits than the defined number of registers.
// Returns: number to display. If an invalid number was read, the number returned is the current number being displayed
//
int readNumberFromPC ()
{
  byte incomingByte;
  int  numberRead;
  byte incomingCount;
  
  if (Serial.available () > 0)
  {
    numberRead = 0;
    incomingCount = 0;
      
    while (Serial.available () > 0)
    {
      incomingByte = Serial.read () - 48;
      incomingCount++;
      
      if (incomingByte < 0 || incomingByte > 9 || incomingCount > g_registers)
      {
        badNumber ();
        return g_numberToDisplay;
      }
      
      numberRead = 10 * numberRead + incomingByte;
      
      // Necessary to get all input in one go.
      delay (10);
    }

    Serial.print ("Now displaying: ");
    Serial.println (numberRead, DEC);
    
    return numberRead;
  }
  
  return g_numberToDisplay;
} // readNumberFromPC


void loop()
{
  g_numberToDisplay = readNumberFromPC ();
  
  if (g_numberToDisplay < 10)
  {
    g_registerArray [3] = g_digits [0];
    g_registerArray [2] = g_digits [0];
    g_registerArray [1] = g_digits [0];
    g_registerArray [0] = g_digits [g_numberToDisplay];
  }
  else if (g_numberToDisplay < 100)
  {
    g_registerArray [3] = g_digits [0];
    g_registerArray [2] = g_digits [0];
    g_registerArray [1] = g_digits [g_numberToDisplay / 10];
    g_registerArray [0] = g_digits [g_numberToDisplay % 10];
  }
  else if (g_numberToDisplay < 1000)
  {
    g_registerArray [3] = g_digits [0];
    g_registerArray [2] = g_digits [g_numberToDisplay / 100];
    g_registerArray [1] = g_digits [(g_numberToDisplay % 100) / 10];
    g_registerArray [0] = g_digits [g_numberToDisplay % 10];
  }
  else
  {
    g_registerArray [3] = g_digits [g_numberToDisplay / 1000];
    g_registerArray [2] = g_digits [(g_numberToDisplay % 1000) / 100];
    g_registerArray [1] = g_digits [(g_numberToDisplay % 100) / 10];
    g_registerArray [0] = g_digits [g_numberToDisplay % 10];
  }

  sendSerialData (g_registers, g_registerArray);
} // loop