So, from figure one and the many examples on Google..
Supply to Opamp - 5V from Power Supply.
Ground common to device being monitored.
Monitored Input to Non-inverting + of OpAmp
Input of Non-inverting - of Opamp tied to Output.
Output has no capacitor or resistor as in Figure 1 - it just goes straight to Analog In of arduino?
Sounds too simple?