user7572: I am building a project that includes an analog Input and several digital Inputs and Outputs.  All of them connect to ground in some way.  Do I need to worry about voltage, coming from the digital outputs, going to ground, and effecting readings on the analog input?  If so, how do I deal with this?

user3638: The arduino has build in pull up resistors, it is not a residue voltage coming from ground more than a "not 100% 0 volt" resistor.
Even though there is built in pull-up resistors one can add additional resistance to the arduino to make sure it will not show a false positive.
From what i have learned, you cannot experience voltage comming from ground (if everything is properly wired), if you want to make sure. Place a diod in the direction of the power flow, to prevent this. 

7572: <p>I am building a project that includes an analog Input and several digital Inputs and Outputs.  All of them connect to ground in some way.  Do I need to worry about voltage, coming from the digital outputs, going to ground, and effecting readings on the analog input?  If so, how do I deal with this?</p>
 3638: <p>The arduino has build in pull up resistors, it is not a residue voltage coming from ground more than a "not 100% 0 volt" resistor.</p>

<p>Even though there is built in pull-up resistors one can add additional resistance to the arduino to make sure it will not show a false positive.</p>

<p>From what i have learned, you cannot experience voltage comming from ground (if everything is properly wired), if you want to make sure. Place a diod in the direction of the power flow, to prevent this. </p>
