rtc values to a string

Projects Programming
1

Hello,
once again I have another problem :slight_smile: this time I'm using an rtc (real time clock) but I want to make an if statment with the time but I don't know how. This is what I tried so far but I got an error.

#include <DS3231.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
DS3231 rtc(SDA, SCL);
int lastTime;
int currentTime;
String time;
void setup() {
  lcd.init();
  rtc.begin();
  rtc.setDOW(FRIDAY);
  rtc.setTime(20, 37, 0);
  rtc.setDate(4, 2, 2021);
  lcd.setCursor(0, 0);
  lcd.backlight();
}
void loop() {
  time = rtc.getTimeStr();
  lcd.clear();
  lcd.print(rtc.getDOWStr());
  lcd.print(" ");
  lcd.print(rtc.getDateStr());
  lcd.print(" -- ");
  lcd.setCursor(0, 1);
  lcd.print(rtc.getTimeStr());
  if(time == 12, 00, 00){
    lastTime = 12;
  }
  if (time >= 13, 00, 00 && lastTime == 12){
    time = time - 12;
  }
  delay(1000);
}

Invalid operands to binary expression ('String' and 'int')

(I'm using arduino IDE 20 beta)

2

This is not a String comparison (look up the "comma operator")

if (time >= 13, 00, 00)

My favorite way of keeping track of day time for alarms, timed events, etc. is to use seconds or minutes past midnight. Then a simple integer if statement works well.

Here is a simple demo that uses that technique to print the date and time every five minutes:

//time library demo: 5 minute interval timer
#include "TimeLib.h"

time_t unixTime; // a time stamp

void setup() {
  Serial.begin(9600);

  // set internal clock time and date. 
  // setTime(hr,min,sec,day,mnth,yr);

  setTime(23,0,0,6,11,2020);
  Serial.print("Starting clock. now() = ");
  Serial.println(now());
  // print as date_time
  print_date_time();
  
  // adjust for DST
  unixTime = now();  //get the unix timestamp
  unixTime += 3600UL; //add DST in spring
  setTime(unixTime);
  Serial.println("After adding DST offset");
  print_date_time();
  Serial.println("Starting loop()");
}

void loop() {
  static int minutes_past_midnight, last_print_time = 0;

  // check the clock
  minutes_past_midnight = hour() * 60 + minute();
  
  // every 5 minutes, print the data and time
  if (minutes_past_midnight != last_print_time && minutes_past_midnight % 5 == 0) {
    last_print_time = minutes_past_midnight;
    print_date_time();
  }
}

void print_date_time() { //easy way to print date and time
  char buf[20];
  snprintf(buf,sizeof(buf),"%02d/%02d/%4d %02d:%02d:%02d", day(), month(), year(), hour(), minute(), second());
  Serial.println(buf);
}
3

Hello,
I don’t really understand that code is there one for the library I’m using?

4

You will have to do some learning one way or another.

If you want to compare Strings or C-strings (which are not the same thing at all), there are tutorials on line explaining how. Search for "C/C++ compare strings". But you will find that the approach does not work well.

The approach I posted can easily be modified to use the functions built into DS3231.h (like getHour() and getMinute(), which return integer values), and are documented here.

5

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