RTC DS1307 module not working

Question

I have a problem with an RTC: it doesn't work correctly. When I try to read date or time, I only see the characters "àààààààà" or or the program is blocked.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <RTClib.h>
DS1307 rtc;
DateTime rtcTime;
void setup() {
 //zainicjowanie generatora liczb losowych
 randomSeed(A0); 
 Wire.begin();
 rtc.begin();
}
void loop() {
 rtcTime = rtc.now();
 int mm = rtcTime.minute();
 Serial.println(mm);
 
 delay(500);
}

This function blocks my program:

String timeRTC(){
 DateTime now = rtc.now();
 String Hour = "0" + String(now.hour()); 
 String Minutes = "0" + String(now.minute()); 
 String Seconds = "0" + String(now.second());
 if (Hour.length() == 3) {
 Hour = Hour.substring(1);
 }
 if (Minutes.length() == 3) {
 Minutes = Minutes.substring(1);
 }
 if (Seconds.length() == 3) {
 Seconds = Seconds.substring(1);
 }
 return Hour+":"+Minutes+":"+Seconds;
}

I can't find what is causing this problem. I use an Arduino Uno in the WOKWI emulator.

String dateRTC(){
 DateTime now = rtc.now();
 String Day = "0" + String(now.day()); 
 String Month = "0" + String(now.month()); 
 String Year = String(now.year());
 if (Day.length() == 3) {
 Day = Day.substring(1);
 }
 if (Month.length() == 3) {
 Month = Month.substring(1);
 }
 return Day+"-"+Month+"-"+Year;
}
String timeRTC(){
 DateTime now = rtc.now();
 String Hour = "0" + String(now.hour()); 
 String Minutes = "0" + String(now.minute()); 
 String Seconds = "0" + String(now.second());
 if (Hour.length() == 3) {
 Hour = Hour.substring(1);
 }
 if (Minutes.length() == 3) {
 Minutes = Minutes.substring(1);
 }
 if (Seconds.length() == 3) {
 Seconds = Seconds.substring(1);
 }
 return Hour+":"+Minutes+":"+Seconds;
}

enter image description here

• Edgar Bonet: Could you provide a link to your WOKWI project?
• Qmails: I use free version of WOKWI. This is link for my project: file.io/y1XjwyqHjhNk
• Edgar Bonet: The link says "The transfer you requested has been deleted."
• Qmails: I shared the file again: easyupload.io/b0e4w8
• Rohit Gupta: What do you mean by "blocked my program"?

Answer 1

You don't have a problem with the RTC: if you call Serial.begin() in setup(), and remove everything in your loop() after Serial.println(mm);, the program works as expected. Your problem is elsewhere. Most likely you are corrupting memory, which leads to unpredictable behavior.

Side note: if you switch to Adafruit's RTClib (called simply "RTClib" in the library manager), you can simplify timeRTC() to this:

String timeRTC() {
 return rtc.now().timestamp(DateTime::TIMESTAMP_TIME);
}