dotmatrix.c

// 2010 Kenneth Finnegan
// Arduino Dot Matrix Clock
// kennethfinnegan.blogspot.com
// http://kennethfinnegan.blogspot.com/2010/02/dot-matrix-arduino-clock.html

// Note: There is commented out code throughout
// that can be uncommented to use a switch on
// pin 13 to toggle the first two columns between
// the date and the current temperature in F read
// from the 10 bit temperature sensor on the DS3232
// A pulldown resistor with the switch to high is
// needed hardware wise. Enjoy.

#include <Wire.h>

// CONSTS
#define DS3232 B1101000

// PINS
#define LED_DATA  11
#define LED_CLK   10
#define LED_LATCH 9
//#define TEMPDISPSEL 13
byte ledcolumn[] = {3,4,5,6,7};

// GLOBAL VARIABLES
byte displaystate[5] = {0};

// FUNCTIONS
void multiplexdisplay();
void downloadtime();
byte DECTOBCD(byte val);
byte BCDTODEC(byte val);

void setup() {
  int i;
  Wire.begin();
  pinMode(LED_DATA, OUTPUT);
  pinMode(LED_CLK, OUTPUT);
  pinMode(LED_LATCH, OUTPUT);
  //pinMode(TEMPDISPSEL, INPUT);
  
  for (i=0; i<5; i++) {
    pinMode(ledcolumn[i], OUTPUT);
  }
}

void loop() {
  downloadtime();
  multiplexdisplay();
}

void multiplexdisplay() {
  static int prevcol = 0;
  int newcol = (prevcol+1)%5;
  // Setup the driver for the next column
  shiftOut(LED_DATA, LED_CLK, MSBFIRST, displaystate[newcol]);
  // Turn off previous column
  digitalWrite(ledcolumn[prevcol], LOW);
  // Pulse latch to update driver output as quickly as possible
  digitalWrite(LED_LATCH, HIGH);
  // Turn on new column
  digitalWrite(ledcolumn[newcol], HIGH);
  digitalWrite(LED_LATCH, LOW);
  prevcol = newcol;
}

void downloadtime() {
  int second, minute, hour, mhour, day, month;
  Wire.beginTransmission(DS3232);
  Wire.send(0x00);
  Wire.endTransmission();
  Wire.requestFrom(DS3232, 6);
  second = BCDTODEC(Wire.receive() & 0x7F);
  minute = BCDTODEC(Wire.receive());
  hour   = BCDTODEC(Wire.receive() & 0x3F);
                    Wire.receive(); // Ignore day of week
  day    = BCDTODEC(Wire.receive());
  month  = BCDTODEC(Wire.receive() & 0x7F);
  
  displaystate[0] = month;
  displaystate[1] = day;
  mhour = (hour%12==0)?12:hour%12;
  displaystate[2] = (hour/12)<<6 | mhour;
  displaystate[3] = minute;
  displaystate[4] = second;
  
  /* Temperature display easter egg!!!
  if (digitalRead(TEMPDISPSEL)) {
    Wire.beginTransmission(DS3232);
    Wire.send(0x11);
    Wire.endTransmission();
    Wire.requestFrom(DS3232, 2);
    long temp = 32;
    temp += (Wire.receive() * 9) / 5;
    temp += (Wire.receive() >> 5) / 5;
    // Convert to Fahrenheit
    displaystate[0] = temp/10;
    displaystate[1] = temp%10;
    
    // Tell the DS3232 to perform a temperature conversion
    // every second instead of the default one every 64 seconds
    static int prevconv=0;
    if (prevconv != millis()/1000) {
      prevconv = millis() / 1000;
      Wire.beginTransmission(DS3232);
      Wire.send(0x0E);
      Wire.send(B00100000);
      Wire.endTransmission();
    }
  }*/
}
  
  
// Not actually used, but is needed to update time on DS3232,
// if you were not lazy enough to actually bother implementing
// a button system to set the clock.
byte DECTOBCD(byte val) {
  return ((val/10)<<4) + (val%10);
}
byte BCDTODEC(byte val) {
  return (val>>4) * 10 + (val & 0xf);
}