Clocks, I2C, Serial and You

I bought a bunch of parts awhile back with the good intention of building a bright, blue LED clock for my desk at work. Unfortunately, I got side tracked and the parts sat in my parts bin for a month or two. When I had a little too much caffeine in my system last weekend, I hit the parts box and built that clock. Needless to say it wasn't as easy as it looked...Parts List

• 1x Arduino
• 1x Sparkfun Serial 7-Segment Display
• 1x Macetech Chronodot
• 1x Solderless Breadboard

Wiring

• SFE Display Slave Select to Pin 10
• SFE Display MOSI to 11
• SFE Display MISO to 12
• SFE Display SCK to 13
• SFE Display VCC to 5v
• SFE Display GND to GND
• Chronodot SDA to Arduino Pin 4
• Chronodot SCL to Arduino Pin 5
• Chronodot VCC to 5v
• Chronodot GND to GND

CodeThe code below is a modified version of the Chronodot demo code. If you uncomment the set_time() call, it will set the time to the HH:MM passed to the function.

#include #include int ss = 10; //csnint mosi = 11;int miso = 12;int sck = 13;void setup(){//chronodotWire.begin();//DisplaySerial.begin(9600);//Set baudSerial.write(0x7F);Serial.write(0x02);//Reset displaySerial.write(0x7A);Serial.write(0x76);//Set brightnessSerial.write(0x7A);Serial.write(0x01);//Set colonSerial.write(0x77);Serial.write(0x10);// clear /EOSC bit// Sometimes necessary to ensure that the clock// keeps running on just battery power. Once set,// it shouldn't need to be reset but it's a good// idea to make sure.Wire.beginTransmission(0x68); // address DS3231Wire.send(0x0E); // select registerWire.send(0b00011100); // write register bitmap, bit 7 is /EOSCWire.endTransmission();//set_time(23, 59, 00);}void loop(){// send request to receive data starting at register 0Wire.beginTransmission(0x68); // 0x68 is DS3231 device addressWire.send(0); // start at register 0Wire.endTransmission();Wire.requestFrom(0x68, 3); // request three bytes (seconds, minutes, hours)while(Wire.available()){int seconds = Wire.receive(); // get secondsint minutes = Wire.receive(); // get minutesint hours = Wire.receive();   // get hoursseconds = (((seconds & 0b11110000)>>4)*10 + (seconds & 0b00001111)); // convert BCD to decimalminutes = (((minutes & 0b11110000)>>4)*10 + (minutes & 0b00001111)); // convert BCD to decimalhours = (((hours & 0b00100000)>>5)*20 + ((hours & 0b00010000)>>4)*10 + (hours & 0b00001111)); // convert BCD to decimal (assume 24 hour mode)//Serial.print(hours); Serial.print(":"); Serial.print(minutes); Serial.print(":"); Serial.println(seconds);displayTime(hours, minutes);}//Set colon onSerial.write(0x77);Serial.write(0x10);delay(500);//Set colon offSerial.write(0x77);Serial.write(0x01);delay(1000);}byte decToBcd(byte val){return ( (val/10*16) + (val%10) );}void displayTime(int hours, int minutes){String h_str = String(hours);if(h_str.length() < 2){h_str = '0'+h_str;}String m_str = String(minutes);if(m_str.length() < 2){m_str = '0'+m_str;}String timeStr = h_str;timeStr.concat(m_str);Serial.write(timeStr.charAt(0));Serial.write(timeStr.charAt(1));Serial.write(timeStr.charAt(2));Serial.write(timeStr.charAt(3));}void set_time(int hours, int minutes, int seconds){Wire.beginTransmission(104);Wire.send(0);Wire.send(decToBcd(seconds));Wire.send(decToBcd(minutes));Wire.send(decToBcd(hours));Wire.endTransmission();}