J Koger
Published © GPL3+

Simple Watch Using RTC

The O-Watch Simple Watch code tweaked to use the Arduino Zero's built-in RTC, plus a couple other tweaks.

BeginnerFull instructions provided1 hour5,922
Simple Watch Using RTC

Things used in this project

Hardware components

O Watch Base Kit
O Watch Base Kit

Software apps and online services

Arduino IDE
Arduino IDE


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Simple RTC Watch

The O Watch's Simple Watch example tweaked to use the built-in RTC clock.
 * Simple RTC Watch
 * Demonstrates the use of the Arduino Time library and Arduino Zero Real-Time-Clock (RTC) library to make a simple digital watch
 * Uses Arduino Time library http://playground.arduino.cc/code/time
 * Maintained by Paul Stoffregen https://github.com/PaulStoffregen/Time
 * Uses Arduino Zero RTC library https://www.arduino.cc/en/Reference/RTC
 * Maintained by Arturo Guadalupi https://github.com/arduino-libraries/RTCZero
 * This code is for the TinyScreen+ board by TinyCircuits used by O Watch http://tiny-circuits.com 
 * This example is based on the Simple Watch code created by O Watch on 6 March 2016 http://theowatch.com
 * Modified to use RTC, to set the display brightness based on time of day, and to use __DATE__ and __TIME__
 * to preset the watch's date and time by J Koger 13 March 2016

#include <TinyScreen.h> //include TinyScreen library
#include <RTCZero.h> //include the Arduino Zero's Real Time Clock library
#include <TimeLib.h> //include the Arduino Time library
#include <stdio.h>  // include the C++ standard IO library

/* Create an rtc object */
RTCZero rtc;

// We'll dynamically change these values to set the current initial time
// No need to change them here.
byte seconds = 0;
byte minutes = 45;
byte hours = 9;

// We'll dynamically change these values to set the current initial date
// The preset values are only examples.
byte days = 13;
byte months = 3;
byte years = 16;

int brightness = 15; // We'll set it, 3 - 15 based on time of day

TinyScreen display = TinyScreen(TinyScreenPlus); //Create the TinyScreen object

void setup()
  char s_month[5];
  int tmonth, tday, tyear, thour, tminute, tsecond;
  static const char month_names[] = "JanFebMarAprMayJunJulAugSepOctNovDec";

  display.begin();                            //Initializes TinyScreen board
  display.setFlip(1);                         //Flips the TinyScreen rightside up for O Watch
  display.on();                               //Turns TinyScreen display on
  display.fontColor(TS_8b_White,TS_8b_Black); //Set the font color, font background

  rtc.begin(); // initialize RTC
  // Set the time and date. Change this to your current date and time.
  // setTime(16,19,00,12,3,2016);    //values in the order hr,min,sec,day,month,year

  // Let's be lazy and let the compiler set the current date and time for us.
  // This will be a few seconds off due to the time it takes to compile the
  // .ino file and upload the app. But pretty close.

  // __DATE__ is a C++ preprocessor string with the current date in it.
  // It will look something like 'Mar  13  2016'.
  // So we need to pull those values out and convert the month string to a number.
  sscanf(__DATE__, "%s %d %d", s_month, &tday, &tyear);

  // Similarly, __TIME__ will look something like '09:34:17' so get those numbers.
  sscanf(__TIME__, "%d:%d:%d", &thour, &tminute, &tsecond);

  // Find the position of this month's string inside month_names, do a little
  // pointer subtraction arithmetic to get the offset, and divide the
  // result by 3 since the month names are 3 chars long.
  tmonth = (strstr(month_names, s_month) - month_names) / 3;

  months = tmonth + 1;  // The RTC library expects months to be 1 - 12.
  days = tday;
  years = tyear - 2000; // The RTC library expects years to be from 2000.
  hours = thour;
  minutes = tminute;
  seconds = tsecond;

  rtc.setTime(hours, minutes, seconds);
  rtc.setDate(days, months, years);

void displayTime()

  display.on();                               //Turns TinyScreen display on
  for (int i = 1; i < 5; i++) // Display for 5*1000 milliseconds (5 seconds), update display each second
    // To correctly handle switching date at midnight while the time display is on,
    // update -everything-, not just the seconds.

    display.setFont(liberationSansNarrow_12ptFontInfo);   //Set the font type

    // Get the complete date and time now since they're used for the weekday
    // and brightness calculations.
    months = rtc.getMonth();
    days = rtc.getDay();
    years = rtc.getYear();
    hours = rtc.getHours();
    minutes = rtc.getMinutes();
    seconds = rtc.getSeconds();

    if (hours <= 12)
      brightness = hours + 3; // 0 hours = 3 brightness, noon = 15
    else if (hours >= 18)
      brightness = (24 - hours) * 2 + 2;  // 23 hours = 4 brightness, 18 hours = 14
      brightness = 15; // full brightness all afternoon
    if (brightness < 3)
      brightness = 3;
    if (brightness > 15)
      brightness = 15;
    display.setBrightness(brightness);                  //Set display brightness 0 - 15

   // Print date in US format MM:DD:YY (Switch the order in which day, month, year that you like to use)
    display.setCursor(15,8); //Set the cursor where you want to start printing the date
    if(months < 10) display.print(0); //print a leading 0 if hour value is less than 0
    days = rtc.getDay();
    if (days < 10) display.print(0);

    display.setCursor(30,25); //Set the cursor where you want to start printing the date  
    setTime(hours,minutes,seconds,days,months,2000 +  years);    //values in the order hr,min,sec,day,month,year

    display.setFont(liberationSansNarrow_16ptFontInfo);   //Set the font type

    // display time in HH:MM:SS 24 hour format
    display.setCursor(20,45); //Set the cursor where you want to start printing the time
    if(hours < 10) display.print(0); //print a leading 0 if hour value is less than 0
    if(minutes < 10) display.print(0); //print a leading 0 if minute value is less than 0
    if(seconds < 10) display.print(0); //print a leading 0 if seconds value is less than 0
    display.print(" "); //just a empty space after the seconds
    delay(1000); //display for 1 seconds

  display.off();                               //Turns TinyScreen display off

void loop()
   if (display.getButtons())


J Koger

J Koger

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