Pull up resistors and I2C

Hi everyone !

I'm doing a project of an implementation of a humidity and temperature sensor on a GPS device using the Atmega328P. I'm using arduino for programing.

As you know, I have to connect to A4 and A5 (SDA nd SCL) for I2C communication. Furthermore, the SDA and SCL must be wired to VCC through pull-up resistors. (more info here)

Knowing this, I've done an electronic board for my sensor with pull resistors but I've then realized too lad that the GPS device has already integrated pull resistors for SDA and SCL coming out of its Atmega328p. To sum up, now I have a total of 4 pull resistors with 2 resistors on each side.

When I test my board on a Arduino Uno card, the sensors work very fine as Arduino uno doesn't have any resistors coming of SDA and SCL. At contrary, when I test my board on the Gps module, it seems to have I2C communication issues.

So i'm wondering if the wiring of 4 pull up resistors could actually be the source of problem for I2C communication or it do not affect at all the communcation.

Thanks for your help.

In principle you can connect as many resistors as you want, but the total resistance of all resistors should be 4.7k Ohm.

If you have two resistors per line, you can calculate the total resistance as follows:

Rtotal = (R1 x R2) / (R1 + R2)

I hope it helps to solve your problem.

Yeah I thought so. Thank you !

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