I2C Pull Up Resistors

Hi all,

Just wondering what the impact of having more than one set of pull up resistors on the SDA & SCL lines would be. By this I mean if I had one set at the Arduino end and one set at, say, the DS1307 end?




you'll have resistors parallel, so the resistance will be lower.
For example if You have two 4.7 KOhm resistors, than they will act as 2.35 kOhm.

Here You can find some considerations on I2C and resistors.


Thanks Marco, you have verified what I thought was the case (I am new to electronics at this level, my background is programming). The link you gave me is very enlightening, I have three devices on the bus and had not considered that the number of devices may impact the value of pull up resistors.

Once again thanks