A potentiometer is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used (one side and the wiper), it acts as a variable resistor or Rheostat. Potentiometers are commonly used to control electrical devices such as a volume control of a radio. Potentiometers operated by a mechanism can be used as position transducers, for example, in a joystick.
Potentiometers are rarely used to directly control significant power (more than a watt). Instead they are used to adjust the level of analog signals (e.g. volume controls on audio equipment), and as control inputs for electronic circuits. For example, a light dimmer uses a potentiometer to control the switching of a triac and so indirectly control the brightness of lamps.
Potentiometers are sometimes provided with one or more switches mounted on the same shaft. For instance, when attached to a volume control, the knob can also function as an on/off switch at the lowest volume.
A potentiometer (colloquially called a "pot") is constructed using a semi-circular resistive element with a sliding contact (wiper). The resistive element, with a terminal at one or both ends, is flat or angled, and is commonly made of graphite, although other materials maybe used instead. The wiper is connected through another sliding contact to another terminal. On panel pots, the wiper is usually the center terminal of three. For single-turn pots, this wiper typically travels just under one revolution around the contact. "Multiturn" potentiometers also exist, where the resistor element may be helical and the wiper may move 10, 20, or more complete revolutions, though multiturn pots are usually constructed of a conventional resistive element wiped via a worm gear. Besides graphite, materials used to make the resistive element include resistance wire, carbon particles in plastic, and a ceramic/metal mixture called cermet.
One form of rotary potentiometer is called a String potentiometer. It is a multi-turn potentiometer operated by an attached reel of wire turning against a spring. It is used as a position transducer.
In a linear slider pot, a sliding control is provided instead of a dial control. The resistive element is a rectangular strip, not semi-circular as in a rotary potentiometer. Because of the large opening for the wiper and knob, this type of pot has a greater potential for getting contaminated.
Most (cheaper) "log" pots are actually not logarithmic, but use two regions of different, but constant, resistivity to approximate a logarithmic law. A log pot can also be simulated with a linear pot and an external resistor. True log pots are significantly more expensive.
Logarithmic taper potentiometers are often used in connection with audio amplifiers.
Any three-terminal potentiometer can be used as a two-terminal variable resistor, by not connecting to the third terminal. It is common practice to connect the wiper terminal to the unused end of the resistance track to reduce the amount of resistance variation caused by dirt on the track.
Digitally Controlled Potentiometers (DCP's), or simply Digital Potentiometers can be used in analog signal processing circuits to replace potentiometers. They allow small adjustments to be made to the circuit by software, instead of a mechanical adjustment. It is usually controlled via a serial interface, like I²C or SPI. Some types have non-volatile memory to enable them to retain their last settings before power loss when the power is restored.
The same idea can be used to create Digital Volume Controls, attenuators, or other controls under digital control. Usually such devices feature quite a high degree of accuracy, and find applications in instrumentation, mixing consoles, and other precision systems.
The DCP should not be confused with the digital to analog converter (DAC) which actually creates an analogue signal from a digital one. A DCP only controls an existing analogue signal digitally. However, some DACs using resistive R-2R architecture have been functionally used as DCPs where the (varying) analog signal is input to the reference voltage pin of the DAC and the digitally-controlled attenuated output is taken from the output of the DAC.
One of the most common uses for modern low-power potentiometers is as audio control devices. Both sliding pots (also known as faders) and rotary potentiometers (commonly called knobs) are regularly used to adjust loudness, frequency attenuation and other characteristics of audio signals.
The 'log pot' is used as the volume control in audio amplifiers, where it is also called an "audio taper pot", because the amplitude response of the human ear is also logarithmic. It ensures that, on a volume control marked 0 to 10, for example, a setting of 5 sounds half as loud as a setting of 10. There is also an anti-log pot or reverse audio taper which is simply the reverse of a log pot. It is almost always used in a ganged configuration with a log pot, for instance, in an audio balance control.
The potentiometer can be used as a voltage divider to obtain a manually adjustable output voltage at the slider (wiper) from a fixed input voltage applied across the two ends of the pot. This is the most common use of pots.
The voltage across is determined by the formula:
Although it is not always the case, if is large compared to the other resistances (like the input to an operational amplifier), the output voltage can be approximated by the simpler equation:
As an example, assume
Since the load resistance is large compared to the other resistances, the output voltage will be approximately:
Due to the load resistance, however, it will actually be slightly lower: ≈ 6.623 V.
One of the advantages of the potential divider compared to a variable resistor in series with the source is that, while variable resistors have a maximum resistance where some current will always flow, dividers are able to vary the output voltage from maximum () to ground (zero volts) as the wiper moves from one end of the pot to the other. There is, however, always a small amount of contact resistance.
In addition, the load resistance is often not known and therefore simply placing a variable resistor in series with the load could have a negligible effect or an excessive effect, depending on the load.
Guitar Potentiometers help optimize sound quality.(Bourns Announces New Options to Its Industry-Leading Line of Guitar Potentiometers)
Jan 12, 2012; Available for electric and bass guitars, PDB Series includes no load, left handed, and long bushing potentiometers. No load model...