Potentiometers
A potentiometer, often called a pot, is a variable resistor used to adjust voltage levels in electronic circuits. By rotating a shaft or moving a slider, the user changes the resistance between its terminals, allowing precise control of voltage, current or signal level. Potentiometers are widely used for volume controls, tone controls, brightness adjustment, calibration and many other electronic applications.
What Is a Potentiometer?
A potentiometer is a three-terminal variable resistor that acts as an adjustable voltage divider.
Inside the potentiometer is a resistive track and a movable contact called the wiper. Rotating the shaft or moving the slider changes the position of the wiper along the resistive element, producing a variable output voltage.
Construction
| Part | Function |
|---|---|
| Resistive Track | Provides the total resistance. |
| Wiper | Moves along the track to vary the output. |
| Terminal 1 | One end of the resistive element. |
| Terminal 2 | Wiper connection. |
| Terminal 3 | Opposite end of the resistive element. |
| Shaft or Slider | Allows manual adjustment. |
How It Works
When connected across a voltage source, the potentiometer divides the input voltage into two parts.
The output voltage is taken from the wiper. As the wiper moves, the output voltage changes smoothly between the two end terminals.
Potentiometer Symbol
A potentiometer is represented by the resistor symbol with an arrow pointing to the centre of the resistive element.
Types of Potentiometers
| Type | Description |
|---|---|
| Rotary | Adjusted by turning a shaft. |
| Slide | Adjusted by moving a slider. |
| Trimmer (Preset) | Small adjustable potentiometer for circuit calibration. |
| Dual-Gang | Two potentiometers operated by one shaft. |
| Motorised | Automatically adjusted using a motor. |
| Digital Potentiometer | Electronically controlled using digital signals. |
Linear vs Logarithmic Taper
| Linear (B) | Logarithmic (A) |
|---|---|
| Resistance changes evenly. | Resistance changes logarithmically. |
| Suitable for voltage adjustment. | Ideal for audio volume control. |
| Common in laboratory equipment. | Matches human hearing response. |
Common Resistance Values
Linear
- 500 Ω
- 1 kΩ
- 2 kΩ
- 5 kΩ
- 10 kΩ
- 20 kΩ
- 50 kΩ
- 100 kΩ
Audio (Log)
- 10 kΩ
- 20 kΩ
- 50 kΩ
- 100 kΩ
- 250 kΩ
- 500 kΩ
- 1 MΩ
Applications
- Audio volume controls.
- Bass and treble controls.
- LCD brightness adjustment.
- Power supply voltage adjustment.
- Sensor calibration.
- Motor speed controllers.
- Amplifier gain adjustment.
- Industrial control panels.
- Arduino analogue inputs.
- Test equipment.
Specifications
| Specification | Typical Values |
|---|---|
| Resistance | 100 Ω to 10 MΩ |
| Power Rating | 0.1 W to 5 W |
| Tolerance | ±5%, ±10%, ±20% |
| Rotation Angle | 220° to 300° |
| Operating Life | 10,000–100,000 rotations |
Testing a Potentiometer
- Disconnect power from the circuit.
- Measure the resistance between the two outer terminals.
- The reading should equal the rated resistance.
- Measure between the centre terminal and each outer terminal.
- Rotate the shaft slowly.
- The resistance should change smoothly without sudden jumps.
Common Faults
| Fault | Cause |
|---|---|
| Scratchy sound | Dirty or worn resistive track. |
| Dead spots | Damaged resistive element. |
| Open circuit | Broken internal connection. |
| Loose shaft | Mechanical wear. |
| Intermittent operation | Poor wiper contact. |
Potentiometer vs Rheostat
| Potentiometer | Rheostat |
|---|---|
| Three terminals. | Usually two terminals. |
| Acts as a voltage divider. | Acts as a variable resistor. |
| Typically handles small currents. | Designed for higher currents. |
| Used for signal adjustment. | Used for current control. |
Choosing the Right Potentiometer
- Select the correct resistance value.
- Choose a linear or logarithmic taper depending on the application.
- Ensure the power rating is suitable.
- Choose the correct shaft type and mounting style.
- Consider environmental protection for harsh conditions.
Key Points
- A potentiometer is a three-terminal variable resistor.
- It operates as an adjustable voltage divider.
- Linear potentiometers are used for control circuits.
- Logarithmic potentiometers are preferred for audio volume controls.
- Potentiometers are widely used in electronic equipment for manual adjustment and calibration.