user4594: I am using an Arduino Uno R3.
It is not clear on the schematic whether there are pullups on the A4 and A5 I2C pins.
Are there hardwired pullups or do I have to add them myself?

user368: There are very weak internal pullups, but they are not strong enough to be considered compliant with I2C specs. Supply your own external 2.2k-10kohm pullup resistors.

4594: <p>I am using an Arduino Uno R3.</p>

<p>It is not clear on the schematic whether there are pullups on the A4 and A5 I2C pins.</p>

<p>Are there hardwired pullups or do I have to add them myself?</p>
 368: <p>There are very weak internal pullups, but they are <a href="https://electronics.stackexchange.com/questions/102611/what-happens-if-i-omit-the-pullup-resistors-on-i2c-lines">not strong enough</a> to be considered compliant with I<sup>2</sup>C specs. Supply your own external 2.2k-10kohm pullup resistors.</p>
