Does a potentiometer need a resistor in series between power and ground?
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The important thing is that your potentiometer circuit shares the same ground as your microcontroller. If you leave out the ground connection then you have an open circuit and no current can flow from the potentiometer to the micro.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Both circuits share a common ground with the microcontroller.

There is a difference between the two circuits.


The wiper on Figure 1a can go from 0 V at the bottom to 5 V at the top.
The wiper on Figure 1b can go from 0 V at the bottom to 5/4 V (1.25 V) at the top because R1 and R3 form a potential divider with the maximum voltage give by \$ \frac {R3}{R1 + R3} V_2 \$.


If your micro's analog input is 0 to 5 V then (a) uses the full scale (typically 1024 counts on a 10-bit ADC). (b) would give a maximum of 1024/4 = 256 counts for 1.25 V.