Two programs are used to save code space. The first one should be needed only once to set the battery-backed DS1307 real-time clock. It may also be needed if the battery runs out but the battery life is expected to be quite long, like 7 years or so. It sets the clock according to the Arduino date and time so the system clock on your computer should be accurate for this to set correctly.
Download: file
/*********************

Sketch to set the time and date for the DS1307 Real Time Clock
  with an Adafruit Trinket mini microcontroller

**********************/

// include the library code:
#include <Wire.h>
#include <RTClib.h>

RTC_DS1307 RTC;

void setup() {
  RTC.begin();
  if(!RTC.isrunning()) {
     RTC.adjust(DateTime(__DATE__, __TIME__));
  }
}

void loop() {
}
The main clock code is below.
Download: file
/*********************
Trinket RGB LCD Shield Clock

Example code for the Adafruit RGB Character LCD Shield and Library
for Trinket 

The DS1307 Real Time Clock must be initialized with a separate sketch.

Version 2.0 Use with Arduino IDE Version 1.6.5 or later and Adafruit 
   libraries modified December 2015 or later.  Mike Barela for Adafruit.
**********************/

// include the library code:

#include <Wire.h>
#include <Adafruit_RGBLCDShield.h>  // RGB LCD Shield communications
#include <RTClib.h>                 // DS1307 clock communications

// These defines make it easy to set the backlight color
#define OFF 0x0
#define RED 0x1
#define YELLOW 0x3
#define GREEN 0x2
#define TEAL 0x6
#define BLUE 0x4
#define VIOLET 0x5
#define WHITE 0x7

// The shield uses the I2C SCL and SDA pins. 
Adafruit_RGBLCDShield lcd = Adafruit_RGBLCDShield();

RTC_DS1307 RTC;      // Establish clock object
DateTime Clock;      // Holds current clock time
int8_t offset = 0;   // Hour offset set by user with buttons
uint8_t backlight = WHITE;  // Backlight state

void setup() {
  lcd.begin(16, 2);         // initialize display colums and rows
  RTC.begin();              // Initialize clock
  lcd.setBacklight(WHITE);  // Set to OFF if you do not want backlight on boot
}

void loop() {
  uint8_t buttons;                       // button read value
  uint8_t hourval, minuteval, secondval; // holds the time
 
  DateTime Clock;                    // variable to hold our time
  char* colon = ":";                 // static characters save a bit 
  char* slash = "/";                 //   of memory
  
  Clock = RTC.now();                 // get the RTC time
  
  hourval = Clock.hour()+offset;     // calculate hour to display
  if(hourval > 23) hourval-=24;      // adjust for over 23 hour
  else if(hourval < 0) hourval+=24;  //   or under 0 hours
  
  minuteval = Clock.minute();        // This block prints the time
  secondval = Clock.second();        //  to the LCD Shield
  lcd.setCursor(0,0);
  if(hourval < 10) printzero();      // print function does not print
  lcd.print(hourval);                //   leading zeros so this will
  lcd.print(colon);
  if(minuteval < 10) printzero();
  lcd.print(minuteval);
  lcd.print(colon);
  if(secondval < 10) printzero();
  lcd.print(secondval);

  buttons = lcd.readButtons();  // read the buttons on the shield

  if(buttons!=0) {                     // if a button was pressed
      if (buttons & BUTTON_UP) {       // if up pressed, increment hours
         offset +=1;
       }
      if (buttons & BUTTON_DOWN) {     // if down pressed, decrement hours
         offset -=1;
       }
      if (buttons & BUTTON_SELECT) {   // if select button pressed
         if(backlight)                 // if the backlight is on
            backlight=OFF;             //   set it to off
         else                          // else turn on the backlight if off 
            backlight=WHITE;           //   (you can select any color)
         lcd.setBacklight(backlight);  // set the new backlight state
      }
   }
  lcd.setCursor(0,1);                  // This block prints the date
  if(Clock.month()<10) printzero();    //   to the LCD Shield
  lcd.print(Clock.month());
  lcd.print(slash);
  if(Clock.day()<10) printzero();
  lcd.print(Clock.day());
  lcd.print(slash);
  lcd.print(Clock.year());
  
  delay(1000);  // wait one second
}

void printzero() {  // prints a zero to the LCD for leading zeros
  lcd.print("0");   // a function saves multiple calls to the print function
}
The code displays the clock value and polls the buttons. If the up or down buttons are pressed, the value offset is incremented/decremented. This is added to the RTC clock time to form the hour. A more robust program would have the hour written back to the DS1307 but that one function takes about 300+ bytes of code which is too much for our mighty Trinket.
This guide was first published on Jan 27, 2014. It was last updated on Jan 27, 2014. This page (Code) was last updated on Sep 18, 2019.