Arduino uno working with 3.3v - whats the i2c bus voltage?

[EngIntoHW]

Hi
I have arduino uno connected to the i2c of Max30101.

I want to connect pull up resistors on the i2c lines.

Should I connect them to 5v, even though the Max30101 has 1.8v and 3.3v ?

Thanks.

 

[Pommie]

The pullups should go to the 1.8V line or the Max will get too high a voltage. The datasheet states maximum supply voltage of 2V - what is the 3.3V used for?

Mike.

 

[EngIntoHW]

Hi Mike
Thanks a lot

Yes about the 1.8v, the Arduino uno feeds it 3.3v

About the pull up resistors, since the Arduino uno works at 5v
Shouldn't they be connected to 5v?

The max30101 datasheet says the pins can work up to 6v

 

[Pommie]

The UNO should never make the pins output anything but let them float high via the pullups by making them input. The datasheet is confusing. It states 6V tolerance on page 2 but page 5 states for SDA & SCL an input high voltage of Vdd*0.7. A safe way to connect them is with a level shifter. Section 2.3 of this document explains how two mosfets can be used to do level shifting. If you just want to get it working then I'd connect the pullups to 1.8V.

Mike.
Edit, connecting to 1.8V MAY work but might not on other UNOs.