Nano 33 IoT does not find DS3231 RTC

[Ratti3]

Hi,

I'm having issues getting several of my Nano 33 IoTs to detect a custom made DS3231 PCB.

I have done the following so far:

If I connect with the older Nano, the RTCLib code works and detects the DS3231.
I've tested with and without a battery connected.
If I run the I2C scanner on the 33 IoT it only shows the following:

10:26:33.026 -> I2C scanner. Scanning ...
10:26:33.079 -> Found address: 96 (0x60)
10:26:33.079 -> Found address: 106 (0x6A)
10:26:33.079 -> Done.
10:26:33.079 -> Found 2 device(s).

These 2 devices are always present on the 33 IoT, it does not detect anything on 0x68.

I've tried different 33 IoTs and made more than one of the DS3231 boards, the DS3231 chip is a genuine Maxim Integrated.

I've attached a picture of the circuit diagram. Any ideas please?

Thanks

[J-M-L]

Your 10KΩ for SCL and SDA might be high. can you try with 4.7kΩ and don't they need to be pull-up, not just pass through?

[Ratti3]

Oh wow, you're right. I can't believe I made such as obvious mistake. Even the Adafuit DS3231 circuit diagram shows the SDA/SCL is pullup to 3.3V.

I shall resolder later and update the results.

Thanks

[J-M-L]

have fun

[Ratti3]

Sorted, thanks for pointing me in the right direction.
I pulled up the 10K to 3.3V from the SCL/SDA lines and the DS3231 is detected on 0x68 and works.

Some bodging going on here, I need to redesign the PCBs
And I need to check my other I2C PCBs too

[J-M-L]

nice fall back hack

The correct pullup resistance for the I2C bus depends on the total capacitance on the bus and the frequency you want to operate the bus at (higher frequencies require lower resistance pull-ups to get steeper edges).

I noticed on the PCB the

nixie shield

sounds promising !

[Ratti3]

The resistance will drop as I will have another 2 I2C devices connected, VEML7700 light sensor and a BME280, so the total resistance per line will drop to 3.3K because of parallel resistance.

I'm making several different Nixie clocks using Nano 33 IoT and different Russian tubes. It's all modular. I post all my stuff for free, it will be added to the Arduino project page once complete.

This is the current prototype/1st attempt working thanks to you:

It runs of 5V USB C and can optionally run from 12V (12V gives a higher efficiency with the 175V boost convertor.

[J-M-L]

Nice !!!!