Potentiometers

Overview

Potentiometers are variable resistors which are adjusted mechanically. They may be rotational or linear (sliders). They are called pots for short. Technically, only the three pronged devices may be called potentiometers (top, bottom and wiper), the two-pronged version which is normally used for higher power applications is called a variable resistor or rheostat. They not only used for user interfaces, but also as a cheap mechanical rotation to digital converter.

Resistive Track

The resistive track is most cheap potentiometer is made from graphite. Others may be made from carbon or wound wire.

Taper

The taper is the relationship between position and resistance. It is also sometimes called the “law”.

Labelling

Potentiometers are labelled according to their resistance value and resistance layout of the track (taper).

Resistance

The resistance is of potentiometers is easy to read, a usually indicated by a three-digit number and a multiplier. For example, 100K would symbolise a 100kΩ pot.

Taper

There are two types of taper codes (confusing!).

Taper Old Code New Code
Linear A B
Logarithmic (Audio) C A
Antilog F n/a

Travel (Rotation)

Partial-turn

Partial-turn potentiometers are the most common and cheapest form of potentiometer. The total mechanical travel (rotation) is usually between 250-330°. The total electrical travel is usually less than this, which means there is some dead-zone and the start and end of the travel in where the resistance does not changed.

Partial-turn potentiometers are commonly used in human-operated situations (the potentiometer is rotated by hand). They provide enough resolution for things such as amplifier volume control.

Multi-turn

A common number of turns for multi-turn potentiometers is 10. They are usually MUCH MORE expensive than their partial turn counterparts (as of June 2016, US$20 (100) for a “cheap” 3-turn wire-wound potentiometer).

Multi-turn potentiometers are used when more resolution is required, or the “thing” rotating the potentiometer is going to go through 1 or more revolutions (e.g. if the potentiometer was connected to an axle or pulley which rotated back and forth through 4 revolutions).