Hy @ All I trying eagerly to get the followimg simple code example to run: // Autor / Auteur : Zineb KANDOUSSI (https://www.facebook.com/SchoolSurSeineFR/) // Creation / Création : Le 21/04/2023 // Description : Display the current time, date and temperature on the 20x4 LCD screen / Affichage de l'heure actuelle, la date et la température sur l'écran LCD 20x4 // Inspired from this code : File => Examples => RTClib => ds3231 / inspiré de ce code : Fichier => Exemples => RTClib => ds3231 #include #include #include LiquidCrystal_I2C lcd(0x3F, 20, 4); RTC_DS3231 rtc; char daysOfTheWeek[7][12] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; byte char_temp[8] = { B00100, B01010, B01010, B01110, B01110, B11111, B11111, B01110 }; // for thermometer icon void setup() { rtc.begin(); lcd.begin(); lcd.backlight(); lcd.createChar(0, char_temp); lcd.setCursor(0, 0); lcd.print("RTC_Clock_Test"); lcd.setCursor(7, 1); lcd.print(":)"); delay(5000); lcd.clear(); if (rtc.lostPower()) { // When time needs to be set on a new device, or after a power loss, the // following line sets the RTC to the date & time this sketch was compiled rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); } } void loop() { DateTime now = rtc.now(); //lcd.setCursor(column,row); //------------------------------Date display - Affichage de la date-----------------------------// lcd.setCursor(6, 0); lcd.print(daysOfTheWeek[now.dayOfTheWeek()]); lcd.setCursor(0, 1); lcd.print("Date:"); lcd.setCursor(6, 1); if (now.day() <= 9) { lcd.print("0"); lcd.setCursor(7, 1); lcd.print(now.day(), DEC); } else { lcd.print(now.day(), DEC); } lcd.setCursor(8, 1); lcd.print(":"); lcd.setCursor(9, 1); if (now.month() <= 9) { lcd.print("0"); lcd.setCursor(10, 1); lcd.print(now.month(), DEC); } else { lcd.print(now.month(), DEC); } lcd.setCursor(11, 1); lcd.print(":"); lcd.setCursor(12, 1); lcd.print(now.year(), DEC); //------------------------------Time display -----------------------------// lcd.setCursor(0, 2); lcd.print("Time:"); lcd.setCursor(6, 2); if (now.hour() <= 9) { lcd.print("0"); lcd.setCursor(7, 2); lcd.print(now.hour(), DEC); } else { lcd.print(now.hour(), DEC); } lcd.setCursor(8, 2); lcd.print(":"); lcd.setCursor(9, 2); if (now.minute() <= 9) { lcd.print("0"); lcd.setCursor(10, 2); lcd.print(now.minute(), DEC); } else { lcd.print(now.minute(), DEC); } lcd.setCursor(11, 2); lcd.print(":"); lcd.setCursor(12, 2); if (now.second() <= 9) { lcd.print("0"); lcd.setCursor(13, 2); lcd.print(now.second(), DEC); } else { lcd.print(now.second(), DEC); } //------------------------------Temperature display----------------------------// lcd.setCursor(0, 3); lcd.print("Temp:"); lcd.setCursor(6, 3); lcd.print(rtc.getTemperature()); lcd.setCursor(11, 3); lcd.write((char)223); lcd.setCursor(12, 3); lcd.print("C"); lcd.setCursor(15, 3); lcd.print(char(0)); } Here is a photo of the circuit and wiring: [RTCTest] All cables a colored as follows Brown = Ground, Red = 5 Volt, Orange = Serial data, Yellow = Serial clock. Getting this wiring messed up is nearly out of question. I tried a i2c scanner and got 0x57 and 0x68 as answer describing I2C-Adress of RTC and Temp module. What i miss by scanning the code is 0x3F or 0x27 as common I2C-Addresses for LCD Moduls with I2C port. As library for the LCD i selected LiquidCrystal_I2C.h and checked the availability in libs folder. The code is compiled and uploaded without error msg. I assume the mistake is in lcd definition "LiquidCrystal_I2C lcd(0x3F, 20, 4);" and the lcd-calls. I tried to find similair thread in the forum but hijacking is a no go, so i opened this new thread and hope for a few helping answers. Thks in advance...! Best regards Ede

[image] ede-beton: What i miss by scanning the code is 0x3F or 0x27 as common I2C-Addresses for LCD Moduls with I2C port. As library for the LCD i selected LiquidCrystal_I2C.h and checked the availability in libs folder. What happens if you run an I2C scan with only the display connected? BTW, it does look like the contrast could do with being adjusted. There should be a potentiometer on the back for that.

Whow that was pretty fast @BitSeeker. I have to walk the dog first and try a little later. Here is the read out of the scan by now: 21:03:50.959 -> Scanning... 21:03:50.959 -> I2C device found at address 0x57 ! 21:03:51.024 -> I2C device found at address 0x68 ! 21:03:51.056 -> done 21:03:51.056 -> To be continued Ede

[image] ede-beton: I assume the mistake is in lcd definition "LiquidCrystal_I2C lcd(0x3F, 20, 4);" and the lcd-calls That's not your first problem, if it is one. [image] ede-beton: I tried a i2c scanner and got 0x57 and 0x68 as answer describing I2C-Adress of RTC and Temp module. If the I2C scanner doesn't see the display, neither will your sketch. That's your first problem. Check your wires. And when they look fine, check them again. And then replace them. And only when the I2C scanner starts seeing your display, then worry about your sketch.

Hy @van_der_decken @BitSeeker I followed your recommendations and wired only the LCD to VCC GND SCA and SCL with a brandnew set dupont cables and scanned again. Wiggeling the cables a little the backlight cutting in and out and the I2C-Scanner shows the following read out: 23:45:37.980 -> Scanning... 23:45:38.042 -> No I2C devices found 23:45:38.045 -> 23:45:43.032 -> Scanning... 23:45:43.095 -> No I2C devices found 23:45:49.577 -> 23:45:50.272 -> Scanning... 23:45:51.165 -> Em� 23:45:51.230 -> Unknown error at address 0x33837 23:50:11.222 -> Scanning... 23:50:11.551 -> Unknown error at address 0x01 There might be a loose contact between arduino and display. For now i have no idea how to figure out if its the arduino socket due to extensiv use or driving shield on top, or lcd i2c female connectors got broken. [A2004v1.3] I have a spare I2C controller, its worth waiting for the mood to solder a new controller to the display, or buy 2 ready to use LCD`s for about 15 €. If i measure continuity from the female legs of the I2C-controller to the unused port on below the controller GND and VCC works but SDA and SCL stays OL. I will give it a try with a I2C A1602 LCD tomorrow. Thks so far Ede

[image] ede-beton: If i measure continuity from the female legs of the I2C-controller to the unused port on below the controller GND and VCC works but SDA and SCL stays OL. My guess is that provision has been made to have the shift register mounted directly on the display PCB by populating the area in the top left of the photo. The SDA and SCL probably connect with pads on U7. The PCF8574T on the backpack board usually has an address in the range 0x20 - 0x27 depending on the configuration of pads A0, A1 and A2. With all of them being left open, the I2C address should be 0x27. It might be as @van_der_decken has already mentioned, that one of your DuPont wires is dodgy or not making good contact on the breadboard. That would be the first thing to check before attempting to de-solder the backpack board and replacing it.

[image] ede-beton: its worth waiting for the mood to solder a new controller to the display, You can try it without soldering it to the display.

Thks again for all the helpfull hints. My favorit is Arduino Uno r3 - LCD A2004v.13 - #4 by van_der_decken It´s gentle as a KISS (k)eep (i)t (s)imple (s)tupid. Probably dark british sarkasm. But it hit´s the goal. Simply connecting the second I2C-Controller serial scanning leads to following read out: Scanning... I2C device found at address 0x27 ! I2C device found at address 0x57 ! I2C device found at address 0x68 ! done May be that´s the try @jim-p kept in mind. If not pls share your thought for a noob. If not i will give soldering a try. Can´t be as worth as it is. So pls don´t close this threat until i finaly made it. Best regards Ede

[image] ede-beton: I2C device found at address 0x27 ! And that's your I2C LCD backpack being detected. Change your LCD address in the constructor from 0x3F to 0x27 and give that a try.

[image] ede-beton: May be that´s the try @jim-p kept in mind Yes it is, you don't need to solder the I2C backpack to a display to see if the scanner will detect it. So now you need to unsolder the faulty backpack and solder on the working one.

Just for all who have supported this thread. As You can see soldering is done. [RTC-Clock01] Replacing I2C-Modul and correct LCD-adress the scanner reports. Great place for asking for assistance...! Time for a halve pint pure malt. Best regards Ede

Arduino Uno r3 - LCD A2004v.13

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InquisitiveMind July 16, 2026, 3:49pm 12

Nice to see it's working now.

By the way, if you plan to use the DS3231 beyond this test sketch, I recently published a small DS3231 Service Tool that handles RTC setup and calibration separately from the application sketch. You might find it useful:

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Arduino Uno r3 - LCD A2004v.13

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