Linear Potentiometer (Slider)

Summary

Introduction

The word potentiometer comes from potential, which refers to voltage potential, or difference. A potentiometer then is a device for measuring voltage difference. In fact, a potentiometer is simply a resistor with a variable resistance value. Typically it is composed of a resistive material through which a current is passed. Unlike a static resistor, however, the point at which the current exits the resistive material is variable. Most often this is done by using a brush, which makes electrical contact with the resistive material, and which can be moved using a handle. By moving the brush, the voltage potential being measured can be modified.

It should be noted that linear potentiometer is an ambiguous term. The word linear can refer to the nature of the voltage response curve, or to the physical shape of the potentiometer. In our case, we are refering to the physical shape—that is, a straight line. Another word for physically linear potentiometers is slider. An alternative to the linear potentiometer is the rotary potentiometer, which is essentially the same thing but with a circular shape.

When refering to voltage response curve, the term linear is used to describe the nature of this curve. It is possible to have sliders with linear response, but another common response curve is logarithmic. This is because there are many variables, especially in the world of audio and acoustics, which are logarithmic by nature. For example, we hear “loudness” of audible sound in terms of decibels (dB). Decibels are a logarithmic value. Therefore, to hear an apparent linear change in loudness, we must adjust volume levels logarithmically. Every notch on the volume knob of your stereo system is actually an increase in exponential power. Another example is pitch, where every time you increase pitch by an octave, you are actually doubling the frequency. For controlling these types of variables, a logarithmic potentiometer should be used.

Another type of linear potentiometer is the touch sensor. The major difference between the two is that with the touch sensor, the value of the potentiometer is forgotten when the finger is removed. Sliders are used when a value needs to be maintained between adjustments, such as volume levels on a mixer.

Variations

For audio applications, it can be useful to use the same value to modify two or more signals. For this purpose, it is possible to get stereo pots, which apply the same resistance to two seperate circuits.

Another common application of sliders is in the cross-fader, found on mixers. In a cross-fader, there are two strips of resistive material and two brushes, but on one of the sides, the opposite end of the resistive material is connected to read the voltage value. As the brushes are moved simultaneously, the resistance for one side of the cross-fader reads the inverse value of the opposite side, allowing the volume of one channel to be faded down as the other channel is faded up. Because it is a volume setting, cross-faders are usually logarithmic sliders.

Devices

Panasonic ECG EVA-NF4R15A14

Sources

Digikey.ca CDN$ 8.80

Description: 100mm. Mono. 10 KΩ. Linear.
Datasheet: aol0000ce7.pdf
Resources:
Notes:
Variants: EVA-NF3R15B14, EVA-NF4R15D14, EVA-NF4R15Y14

Media

Images

Video

Circuits

External links & references

sensors/linear_potentiometer_slider.txt · Last modified: 2009/01/25 18:56 by joe
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