# Won't a potentiometer powered by a dc supply cause a short-circuit at lower end of the range?

Many tutorials in the Arduino or Raspberry Pi community simulate an analog sensor with a potentiometer. The potentiometer, being a passive device, is powered from the same DC power source that supplies the microcomputer. Usually, the +5V (or +3.3V) and GND pins on the Arduino or Pi are used for this purpose.

This doesn't seem safe to me. Suppose we turn the potentiometer all the way down in this configuration. The resistance should be 0 Ohms and that should short the DC power supply. Yet, this is just what many tutorials like this one here recommend: https://www.instructables.com/id/How-to-use-Potentiometer-Arduino-Tutorial/

How come? I always include a resistor in series with the potentiometer to avoid this situation but no one else seems to think this necessary. Thanks in advance for any help.

• i think that you are misunderstanding how the potentiometer should be connected to the power supply Commented Nov 9, 2018 at 10:24

A potentiometer has three terminals. The two extremes of the resistive element and the central wiper.

The resistive element always has the same resistance. So it is safe to connect those two extremes to the power supply.

That way the wiper will change the voltage continuously from the supply to ground.

• Thank you for helping me out with this. You are indeed correct! Commented Nov 11, 2018 at 21:02

Common use of a potentiometer involves applying a voltage across it, and then the "wiper" (the moving part) in the middle will have a "divided" voltage. It is essentially two resistors with a wire (wiper) in the middle.

This means that for any given supply voltage, there is a constant resistance across the whole potentiometer. The example on the left below has a 5V supply, and a 1kΩ potentiometer. 5V/1000Ω=5mA The wiper however will have a varying resistance.

The example on the right is what you were thinking of (Use of only the wiper and one other terminal). Observe that it does not divide the voltage. And yes: The current will indeed exceed a safe value when the wiper goes too far.

Here is a link to the interactive simulation of the circuit above. You can drag the slider on the right to move the potentiometer's wiper. While your cursor hovers over the slider, you can see the values of "R1" and "R2", which always add up to 1k.

• Thank you so much for the clear explanation and simulation. You have clarified the concept superbly and I now get it. Thank you so much for your help. Commented Nov 11, 2018 at 21:01