Potentiometer / Rheostat / Trimmer
Resistor
A three-terminal resistor with an adjustable wiper that allows manual control of resistance. Used for volume controls, tuning, and adjustable circuit parameters.
Schematic symbol
Potentiometer / rheostat
How potentiometer / rheostat / trimmer appears in a circuit diagram.
Types & variants
Key specs
Resistance range
Ohm (Ω)Min to max resistance between the two outer terminals (e.g., 0-10kΩ).
Tolerance
%How far the actual value can stray from the marked value (typically ±10-20%).
Power rating
Watt (W)Max power it can handle (typically 0.1-2W for trimmers, 0.5-5W for potentiometers).
Taper
Linear/LogarithmicLinear (B) = equal resistance change per angle. Logarithmic (A) = exponential change, ideal for audio volume.
Temperature coefficient
ppm/°CHow much resistance changes with temperature (lower = more stable).
Markings
Through-hole: Printed resistance value (e.g., '10K'). Trimmers often have tiny markings. SMD: 3-digit code (e.g., '103' = 10kΩ). Taper marked as 'A' (log) or 'B' (linear).
Standard values
Common: 100Ω, 1k, 10k, 100k, 1M. Audio pots typically 10k-100k logarithmic. Trimmers: 100Ω-100k multi-turn.
How to choose
1) Determine required resistance range. 2) Choose linear (B) for most uses, logarithmic (A) for audio volume. 3) Pick power rating > max expected power. 4) Consider physical size and mounting (rotary/slide). 5) Use trimmers for calibration adjustments.
Pinout & package
3 terminals: outer two (fixed resistance), middle (wiper). Packages: rotary, slide, trimmer (PCB mount). SMD versions available. Non-polar.
Example circuits
- Volume control in audio circuits
- Voltage divider for adjustable reference
- Light dimmer circuit
- Position sensor with variable resistor
- Brightness control for LED
Common failures
Wiper contact wear causing scratchy sound or intermittent connection. Dirt/debris on track causing erratic behavior. Mechanical failure (broken shaft). Open circuit from overheating.
How to test
Measure resistance between outer terminals (should match marked value). Move wiper: resistance between wiper and each outer terminal should vary smoothly. Should never be open or short.
Substitutes
Fixed resistor + switch for stepped adjustment. Digital potentiometer for electronic control. Rheostat for high-current applications.