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; }

I use free version of WOKWI. This is link for my project: file.io/y1XjwyqHjhNk — Qmails
– Qmails, Commented Jan 23, 2024 at 10:34
The link says “The transfer you requested has been deleted.” — Edgar Bonet
– Edgar Bonet, Commented Jan 23, 2024 at 10:41

Edgar Bonet · Accepted Answer · 2024-01-23 11:25:20Z

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); }

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