Problem with custom PCB and DS3231

Hey guys,

I'm currently working on a project for which I created a custom PCB.
On the PCB is a RTC Modul soldered. (The DS3231)

If I only use the Arduino Nano with the DS3231 and run the I2C Scanner of Nick Gammon,
it detects the RTC and the eeprom of the RTC:

I2C scanner. Scanning ...
Found address: 87 (0x57)
Found address: 104 (0x68)
Done.
Found 2 device(s).

But if I try the exact same thing on my PCB with an Arduino Nano and a DS3231
it does not find any I2C address.

Maybe someone can help me finding my problem? Thanks! :neutral_face:


Picture 1

Picture 2

If I only use the Arduino Nano with the DS3231 and run the I2C Scanner of Nick Gammon,
it detects the RTC and the eeprom of the RTC:

If you use that variant do you power the DS3231 by 3V3 too? The DS3231 is 5V safe, so you can power it by 5V and if you do that you don't over-voltage the I2C signals.

The Nano's 3V3 pin is powered by the FTDI chip so you must not draw much power from it.

make sure to use the pull-up resistors on the I2C bud snd no, not the internal 10K ones. try 1K or so.

make sure to use the pull-up resistors on the I2C bud snd no, not the internal 10K ones. try 1K or so.

1k is outside I2C specs for 3V3 as well as 5V. Use 2k2 for 3V3 and 4k7 for 5V.