Potentiometer Wiring and Pinout: Identification, Calculations, and Testing

A three-terminal mechanical potentiometer contains two fixed end terminals and a movable wiper. It can operate as a voltage divider, where the wiper provides a position-dependent voltage, or as an adjustable two-terminal resistance when the exact device permits rheostat operation. Correct design requires identifying the terminal view, accounting for load resistance and source impedance, and checking element voltage, power, wiper current, taper, and environmental ratings.

Catalog

Figure 1. Potentiometer Wiring

Identify the Potentiometer Terminals

End Terminals and Wiper

A mechanical potentiometer contains a resistive track with one terminal at each end. A movable contact, called the wiper, travels across the track as the shaft rotates. The three terminals can therefore be described as End A, Wiper, and End B without assigning fixed electrical roles.

The nominal total resistance, R_T, is measured between End A and End B. Rotation changes the resistance from End A to the wiper, R_AW, and from the wiper to End B, R_WB. For an unloaded device in good condition:

R_AW + R_WB ≈ R_T

Small differences can result from end resistance, contact resistance, meter accuracy, and manufacturing tolerance. The end-to-end resistance itself should remain nearly constant during rotation. The Vishay application note distinguishes total resistance, end resistance, contact resistance, electrical travel, and mechanical travel [1].

Multimeter Pin Test

Identify the terminals with power removed and the potentiometer disconnected from other components. Parallel circuit paths can otherwise produce misleading resistance readings.

• Set the multimeter to a resistance range above the marked potentiometer value.

• Measure all three terminal pairs. The pair that remains close to the marked total resistance while the shaft rotates is the two end terminals.

• The remaining terminal is the wiper. Measure from the wiper to each end while rotating the shaft. One reading should rise as the other falls.

For a 10 kΩ linear potentiometer near its electrical midpoint, the two wiper-to-end measurements may each be near 5 kΩ. They are not expected to be exact because the mechanical midpoint may not equal the electrical midpoint, and the track has tolerance and conformity error.

Dual-gang, switched, and tapped potentiometers have more terminals. In those cases, isolate one gang using the circuit diagram in the exact datasheet. Physical position alone is not a dependable way to identify every terminal.

Figure 2. Generic Three-Terminal Potentiometer Identification

Rotation Direction and Terminal View

A datasheet pinout is valid only from its stated viewing direction, such as the shaft side, terminal side, or PCB side. Mirroring that view reverses the apparent terminal order.

For an output that rises during clockwise rotation, connect the intended ground end temporarily and measure between that end and the wiper. The wiper-to-ground resistance should increase as the shaft turns clockwise. If it decreases, exchange the two end-terminal connections. The wiper connection does not need to move.

This measurement is safer than assuming that the left terminal is ground or that terminal 2 is always physically centered.

For the Vishay P10 only, the manufacturer circuit diagram identifies terminal 2 as the wiper and terminals 1 and 3 as the resistive-element ends. Do not transfer this numbering to another potentiometer without checking its datasheet. [5]

Choose the Wiring Mode

Voltage Divider Connection

A voltage divider uses all three terminals:

• Connect End A to V_IN

• Connect End B to the circuit reference or ground

• Take V_OUT from the wiper

The wiper divides the track into an upper resistance and a lower resistance. Swapping End A and End B reverses the direction in which the output changes, but it does not change the nominal end-to-end resistance.

The receiving circuit loads the wiper. A low input resistance changes the divider ratio and may prevent the output from following the expected position. The output can also stop short of the supply rails because of end resistance, limited electrical travel, and load current.

Rheostat Connection

A potentiometer used as an adjustable two-terminal resistance is commonly described as a rheostat connection. Connect the wiper and either one of the end terminals. The selected end determines whether resistance rises or falls for a given rotation direction.

The unused end may be left open. For devices whose datasheet permits this connection, the otherwise unused end may be tied to the wiper. If wiper-to-track contact is interrupted, this arrangement can provide a resistance path through the remaining track instead of leaving the external circuit open; it does not remove the need to check wiper current and partial-track power.

Do not tie End A directly to End B and then use the wiper as the second terminal. That connection places the two track sections in parallel. The resistance approaches zero at both ends and reaches approximately R_T / 4 near the midpoint, which produces a nonmonotonic control response.

Some potentiometric position sensors are designed only for high-impedance voltage-divider service. The Murata SV Series application note specifies at least 1 MΩ connection impedance for the wiper and warns against a rheostat connection because that series has relatively high contact resistance [2]. This restriction applies to the named series, not to every mechanical potentiometer.

Figure 3. Voltage Divider and Rheostat Connections

Wiring Mode Decision Table

Connection	Terminals Used	Controlled Quantity	Main Load Concern
Voltage divider	Both ends and wiper	Output-voltage ratio	Wiper load changes the ratio
Rheostat, unused end open	Wiper and one end	Series resistance or current	Circuit current passes through the wiper
Rheostat, unused end tied to wiper	Wiper tied to one end, opposite end used	Series resistance with an alternate full-track path during some wiper-contact interruptions	Wiper current and product suitability

Calculate the Electrical Result

Ideal Divider Output

Let R_U be the resistance from V_IN to the wiper and R_D the resistance from the wiper to ground. For an unloaded divider:

V_OUT = V_IN × R_D / (R_U + R_D)

Here, V_IN and V_OUT are in volts, while R_U and R_D can use any common resistance unit. Near the ground end, R_D approaches its minimum value and V_OUT approaches 0 V. Near the input end, R_U approaches its minimum value and V_OUT approaches V_IN.

An ideal linear taper produces approximately half the input voltage at half electrical travel. A mechanical shaft position marked as halfway may not represent exact half electrical travel.

Loading Error and Source Impedance

If a resistive load R_LOAD is connected from the wiper to ground, it appears in parallel with R_D. The loaded output becomes:

V_OUT = V_IN × (R_D ∥ R_LOAD) / [R_U + (R_D ∥ R_LOAD)]

where:

R_D ∥ R_LOAD = (R_D × R_LOAD) / (R_D + R_LOAD)

A receiving circuit referenced to another voltage, or one containing active input bias, cannot automatically be represented by R_LOAD.

The wiper also has a position-dependent Thevenin source resistance:

R_SOURCE = R_U ∥ R_D

For a uniform linear track, the maximum occurs near mid-travel:

R_SOURCE,max = R_T / 4

A buffer can isolate the divider when the load produces excessive ratio error. ADC inputs require a separate acquisition-time check because their internal sampling capacitor must settle through the source resistance. Microchip AN693 explains that the required acquisition time depends on source impedance and the converter's internal input network [3]. The acceptable value must come from the selected ADC or microcontroller datasheet.

Worked 5 V Divider Example

Consider a calculated design scenario with these known values:

• V_IN = 5.0 V

• R_T = 10 kΩ, linear taper

• Midpoint values R_U = R_D = 5 kΩ

• R_LOAD = 100 kΩ

Without the load:

V_OUT = 5.0 × 5000 / (5000 + 5000) = 2.50 V

With the 100 kΩ load:

R_D ∥ R_LOAD = 5 kΩ ∥ 100 kΩ = 4.762 kΩ

V_OUT = 5.0 × 4.762 / (5 + 4.762) = 2.439 V

The error relative to the ideal midpoint is:

(2.439-2.500) / (2.500)×100=-2.44%

Figure 4. Loaded 5 V Divider Example

The example shows that a load ten times the total potentiometer resistance still creates a visible ratio error. The maximum unloaded source resistance is 10 kΩ/4=2.5 kΩ. Both figures should be checked against the accuracy and settling requirements of the receiving circuit.

Check the Datasheet Ratings

Resistance Value and Taper

At a fixed applied voltage, a lower total resistance increases divider current and total-element dissipation but reduces source impedance; a higher resistance reduces standing current but increases sensitivity to load resistance, leakage, noise pickup, and ADC acquisition requirements.

End-to-end resistance tolerance does not directly become the same percentage of unloaded divider-ratio error because both track sections belong to the same element. It still affects divider current, source impedance, loading, and power. Taper conformity, end resistance, and wiper contact behavior affect the relationship between position and output.

Taper letters are series-specific, as shown by two official datasheets: [5], [6]

Manufacturer and Series	Code A	Code B
Vishay P10	Linear	Not listed as the standard P10 taper
Bourns PTB	Audio	Linear

This comparison concerns code meaning only. It does not compare power, service life, or other performance because the two series use different formats and specifications.

Voltage, Power, and Wiper Current

Three limits require separate checks. The power rating limits heating in the resistive element. Maximum working or limiting element voltage can restrict the applied voltage even when V²/R is below the power rating. Wiper current limits the moving contact, especially in rheostat service.

For a voltage applied across the full track, let V_T be the DC voltage—or the RMS voltage for a resistive AC calculation—across the element:

P_T = V_T² / R_T

The following values are from the Vishay P10 resistance-element table. They apply to this series and the stated resistance values. [5]

P10 Total Resistance	Maximum Power at 70 °C	Maximum Working Voltage	Maximum Wiper Current
1 kΩ	0.5 W	22.4 V	22.4 mA
10 kΩ	0.5 W	70.7 V	7.1 mA

The same 0.5 W power entry does not produce the same allowable current for both resistances. Operation above 70 °C must follow the P10 derating curve. A rheostat also uses only part of the track at many settings, so the full-element power number should not be assigned to a small active segment. Use the resistance-specific wiper-current and operating data provided by the manufacturer.

These beginner wiring procedures are for low-voltage electronics. A potentiometer with a high element-voltage entry is not automatically suitable for hazardous or mains-connected controls. Insulation, enclosure, spacing, approvals, failure protection, and user-accessible metal parts require a separate safety design.

Mechanical Life and Environment

Mechanical travel can exceed electrical travel. The Vishay P10, for example, specifies 290° ± 5° mechanical travel and 250° ± 15° electrical travel. Its datasheet also lists IP67 sealing and 10,000-cycle mechanical life [5]. These are product-specific specifications, not general values for rotary potentiometers.

Electrical travel affects how much shaft movement produces a changing output. Sealing and cycle life influence suitability for dusty panels, exposed controls, calibration points, or frequently adjusted interfaces. Temperature, vibration, contamination, shaft loading, soldering process, and panel mounting can also alter reliability.

Check the terminal style and mechanical drawing before laying out a PCB or panel. A correct schematic cannot compensate for a mirrored footprint, an unsupported shaft, or a housing that allows cleaning fluid and debris to reach the track.

Build Practical Circuits

Microcontroller ADC Input

For a ratiometric measurement, connect the potentiometer across a supply or reference rail that is also used by the ADC as its conversion reference, provided that the rail or external reference source is designed to supply the potentiometer current. Do not assume that a dedicated VREF input pin can source this current. In the ideal case, a proportional change in that supply changes both the wiper voltage and the ADC full-scale reference, so the reported position remains nearly constant.

Figure 5. Ratiometric ADC Connection

The reference source must be able to supply the potentiometer current.

Keep the wiper voltage within the ADC input range under every operating condition. The grounds must share the same reference. For the 10 kΩ example, the worst-case source resistance is approximately 2.5 kΩ at mid-travel, but that number alone does not prove compatibility. Channel-switching rate, sampling capacitance, acquisition time, leakage, and any external filter also affect settling.

A capacitor from the ADC input to ground can reduce high-frequency noise, but it also changes response time and charging current. Choose its value using the ADC input model and required control bandwidth. A voltage follower may be used when the input load or sampling process produces unacceptable error.

Calculated LED Rheostat Example

A small LED circuit can demonstrate rheostat operation, but the potentiometer must not replace the fixed current-limiting resistor. Consider this calculated example:

• Supply voltage, V_S = 5.0 V

• Fixed resistor, R_F = 330 Ω

• Vishay P10 linear potentiometer, R_POT = 0 to 1 kΩ

• Vishay TLUR5400 red LED

The modeled 0–1 kΩ adjustment range is idealized because the P10 specifies typical end resistance and finite electrical travel; the realized endpoint resistance and active shaft span are therefore product-specific. [5]

The TLUR5400 datasheet lists a typical forward voltage of 2 V and a maximum of 3 V at the 20 mA test condition, together with a 20 mA DC absolute-maximum forward current at 25 °C ambient unless otherwise specified. The following estimate assumes V_F = 2.0 V, even though the calculated current is below that test current. It is a design estimate, not a measured result or guaranteed current. [4]

I_LED = (V_S - V_F) / (R_F + R_POT)

At the minimum potentiometer resistance:

I_LED ≈ (5.0 - 2.0) / 330 = 9.1 mA

At R_POT = 1 kΩ:

I_LED ≈ 3.0 / 1330 = 2.26 mA

Figure 6. Calculated 5 V LED Rheostat Example

Potentiometer dissipation is:

P_POT = I_LED²R_POT

Under the constant-V_F assumption, potentiometer dissipation is highest near R_POT = 330 Ω and is approximately 6.8 mW. The Vishay P10 datasheet lists a 0.5 W maximum power rating at 70 °C and a maximum wiper current of 22.4 mA for the 1 kΩ element. Under the stated V_F = 2.0 V assumption, the highest calculated circuit current is 9.1 mA. The P10 table provides the 22.4 mA value for the 1 kΩ element, but the datasheet does not explicitly describe this LED circuit as a manufacturer-approved rheostat application. [5]

Final hardware should be checked with maximum supply voltage and the LED's actual forward-voltage behavior. A driver with PWM provides more efficient and predictable control for high-power LEDs.

Passive Audio Level Control

A passive volume control uses the potentiometer as a signal divider. Connect the audio source to one end, signal ground to the other, and the wiper to the amplifier input. The amplifier input resistance should be high relative to the potentiometer so that loading does not distort the intended attenuation curve.

Audio controls commonly use a logarithmic or audio taper because equal shaft increments then provide a response closer to perceived loudness. The taper letter must be verified in the exact datasheet. Stereo equipment normally uses a dual-gang part with a channel-tracking specification.

This connection attenuates a small signal. It is not intended to drive a loudspeaker directly. DC bias, source resistance, input resistance, and coupling-capacitor requirements depend on the surrounding amplifier circuit.

Recommended Wiring Test and Troubleshooting Method

The following is a recommended validation procedure, not author-reported experimental data.

For E-E-A-T traceability, an actual test record must identify the potentiometer manufacturer and part number; nominal resistance and taper; supply voltage; load resistance; ambient temperature; DMM model and its stated resistance/voltage accuracy; shaft position; end-to-end resistance; both wiper-to-end resistances; and loaded and unloaded wiper voltage.

Pre-Power Resistance Checks

Complete these checks before applying power:

• Confirm that the end-to-end resistance remains nearly constant through the full rotation.

• Confirm that each wiper-to-end resistance changes smoothly and in the opposite direction to the other.

• Verify that the selected ground end gives the required clockwise response.

• Inspect for solder bridges, an unintended connection between both end terminals, and a mirrored PCB footprint.

• Measure resistance from the supply node to ground and check for an unexpected short.

Apply power with a current-limited low-voltage source. Measure the wiper voltage at both electrical endpoints and near the midpoint, first without the intended load and then with it connected. The difference between those two measurements reveals loading that a resistance-only test cannot show.

Symptom-Based Fault Diagnosis

Symptom	Likely Cause	Test and Corrective Action
Output decreases clockwise	End terminals are reversed	Exchange End A and End B while leaving the wiper connection unchanged
Output stays near one rail	Wiper is open, shorted to an end, or connected to the wrong PCB pad	Power down, measure both wiper-to-end resistances, and trace the wiper pad
Resistance falls at both shaft extremes	Both end terminals are tied together	Remove the end-to-end short and use one end plus the wiper for rheostat service
Loaded midpoint voltage is lower than expected	Receiving input resistance is too low	Measure the load resistance, calculate the loaded divider, or add a buffer
ADC value settles slowly or changes after channel switching	Source resistance and filter capacitance exceed the available acquisition time	Check the ADC input model, extend acquisition time, reduce resistance, change the filter, or buffer the wiper
Output jumps or becomes noisy during rotation	Worn or contaminated contact, poor solder joint, intermittent wiring, or unsuitable load current	Inspect joints, measure resistance during slow rotation, and replace the device if discontinuities remain
Potentiometer becomes warm	Element power, wiper current, or applied voltage exceeds the selected part's operating limit	Remove power and calculate all three limits using worst-case conditions and derating
Output does not reach exactly 0 V or VIN	End resistance, limited electrical travel, or load current	Compare the measured endpoint values with the datasheet and loaded-divider calculation

Conclusion

Reliable potentiometer wiring starts by identifying the two end terminals and wiper, then assigning their roles from the intended circuit instead of physical position alone. Divider applications require loading and source-impedance checks, while rheostat applications require separate checks for current, voltage, partial-track power, and product suitability. A power-off resistance test followed by current-limited endpoint and midpoint voltage measurements can expose pinout, loading, and wiring faults before the circuit enters service.

Technical References

[1] Vishay Intertechnology, Potentiometers and Trimmers Application Note, Document 51001, Revision 02-Aug-2013.

[2] Murata Manufacturing Co., Ltd., SV Series Product Application Note, Document DM-SA16-033, Revision 1.2, February 2018.

[3] Microchip Technology Inc., AN693: Understanding A/D Converter Performance Specifications, DS00693A, 2000.

[4] Vishay Intertechnology, TLUR5400, TLUR5401 Red LED Datasheet, Document 83055, Revision 2.3, 06-Sep-2022.

[5] Vishay Intertechnology, P10 Potentiometer Datasheet, Document 51030, Revision 13-Mar-2026.

[6] Bourns, Inc., PTB Series Low Profile Slide Potentiometer Datasheet, Revision 08/20.

Frequently Asked Questions [FAQ]

1. Should an ADC's Internal Pull-Up or Pull-Down Be Enabled When Reading a Potentiometer?

Usually not. The internal resistor becomes an additional load, shifts the divider ratio, and can make the position response nonlinear. Disable it unless that loading is intentional. If the design needs a defined state during a fault, use an external network sized so the calculated loading error remains acceptable.

2. How Can Software Reduce Small ADC Fluctuations Without Hiding a Hardware Fault?

First check grounding, acquisition time, contact condition, and any analog filter. Then apply modest averaging, low-pass filtering, or a small deadband. Retain separate diagnostics for abrupt jumps, impossible values, and an open-wiper indication so filtering does not conceal a connection fault.

3. What Changes When the Wiper Signal Runs Through a Long Cable?

Cable resistance and capacitance, shared-ground error, electromagnetic interference, and electrostatic discharge can affect the reading. Route the signal with its reference return, add shielding or protection where the environment calls for it, and use a receiver-side filter or buffer when the source-impedance and settling checks justify one. Validate the circuit with the actual cable length and operating environment.

4. How Can a Controller Detect an Open Potentiometer Wiper?

An intentional high-value pull-up or pull-down at the receiver can move an open wiper toward a diagnostic region. Select the resistor with the loaded-divider calculation, then verify normal endpoints and each expected fault state. Firmware can add range, rate-of-change, and persistence checks, but the threshold must allow for component tolerance and noise.

5. How Should a Dual-Gang Audio Potentiometer Be Evaluated for Channel Matching?

Use the exact datasheet's channel-tracking specification, then compare both gang outputs at the same shaft positions with equal source and load conditions. Check several positions across the usable control range because total-resistance tolerance alone does not establish channel tracking.