Atlas Scientific EZO Flow Meter Pull up resistors

Hi Kyle,

I just need to check some information with you. In the Hydroponic documention under Connecting the Sensors Note 2. It says that you don’t use pull up resistors on the SDA and SCL lines. However whilst looking at the Atlas EZO Flow meter totalizer documents it shows a diagram using 4.7K pull up resistors on both SDA and SCL whilst connecting to the Raspberry PI 4. In addation to this there own carrier board has the resistors installed. So is this safe as I will be using a number of sensors on the same bus? I’ve attached the document if this helps.


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Hi, Chris. Raspberry Pis (and many other single board computers and microcontrollers) have internal pull-up resistors on the I2C’s SDA and SCL lines enabled by default. Therefore, it is not necessary to add additional resistors since only one per line is required for any number of devices that are connected. If additional resistors are added, this is essentially resistors in parallel and will reduce the overall resistance in the circuit and increase the current. If the resistance becomes too low, the current at SDA or SCL may exceed their limit and the pins may become damaged. Many breakout boards with I2C pull-up resistors installed have traces that can be cut to disconnect the pull-up resistors, and should be done if you know the lines already have them installed.

Thanks Kyle I thought I would just check before I get carried away.