Blue Potentiometer Pinout: 3296W & 3386P Trimpot Wiring Guide

The middle pin on any standard blue PCB-mount potentiometer—whether it is a multi-turn Bourns 3296W or a single-turn 3386P trimpot—is always the wiper (Pin 2). Pin 1 is the counter-clockwise (CCW) fixed terminal, and Pin 3 is the clockwise (CW) fixed terminal. When viewing a top-adjust 3296W trimpot from the top with the pins pointing downward, Pin 1 is on the left, the wiper is in the center, and Pin 3 is on the right.

Blue trimpots are ubiquitous on Arduino sensor modules (like the LM393 sound sensor or IR obstacle avoidance boards), DAC feedback loops, and DIY audio preamps. However, cheap clone manufacturing and worn-off silkscreen markings frequently lead to wiring errors. Below is the definitive bench reference for identifying, interpreting, and wiring these components.

Blue Potentiometer Pinout & Physical Layout Reference

The electrical function of the pins never changes, but the physical orientation depends entirely on the package style. The two most common blue trimpots you will encounter are the 3296W (multi-turn, top-adjust) and the 3386P / 3362P (single-turn, top or side-adjust).

Schematic Symbols and Regional Standards

When reading a schematic to determine how the blue trimpot should be wired, you must recognize which drawing standard the engineer used. The physical component remains identical, but the symbol on the page changes depending on the region and the CAD software's default library.

For a deeper look at how these symbols translate to actual circuit behavior, the All About Circuits guide on potentiometers provides an excellent breakdown of the internal resistive track mechanics.

Rows and Markings People Get Wrong

Even when you know the standard pinout, real-world bench conditions introduce variables that cause wiring mistakes. Here are the most common failure points when working with blue trimpots.

1. Faded or Missing Silkscreen Markings

On unbranded clone 3296W trimpots (often found in bulk AliExpress sensor kits), the white '1', '2', and '3' ink rubs off after a few turns of a flathead screwdriver. If you cannot read the pins, do not guess. Use this 60-second multimeter sweep test:

1. Set your digital multimeter (DMM) to the Ohms (Ω) setting.
2. Place probes on the two outer pins. Note the reading (e.g., 10.2 kΩ). This is your total track resistance. Leave the probes here for step 3.
3. Move one probe to the middle pin. Turn the adjustment screw 10 full rotations counter-clockwise.
4. If the resistance drops to near zero (typically < 3Ω for genuine Bourns components, but up to 20Ω on cheap clones), the probe you moved was on Pin 3 (CW), and the stationary probe is on the Wiper (Pin 2).
5. If the resistance stays near the total track value, you moved the probe from Pin 1 to Pin 3, meaning the middle pin is confirmed as the wiper.

2. Misinterpreting Resistance Codes

Blue trimpots use a 3-digit EIA resistance code stamped on the top. A common error is reading '103' as 103 ohms.

• 102 = 10 × 10² = 1,000 Ω (1 kΩ)
• 103 = 10 × 10³ = 10,000 Ω (10 kΩ) — The standard for Arduino 10-bit ADC inputs
• 104 = 10 × 10⁴ = 100,000 Ω (100 kΩ) — Common in audio op-amp feedback loops
• 502 = 50 × 10² = 5,000 Ω (5 kΩ)

3. The 'Floating Wiper' Noise Issue

When wiring a blue trimpot as a variable resistor (rheostat) rather than a voltage divider, beginners often connect only to Pin 1 and Pin 2 (the wiper), leaving Pin 3 floating. As the wiper vibrates or oxidizes, it can momentarily lift off the carbon track, creating an open circuit (infinite resistance) that causes massive voltage spikes or audio pops.

The Fix: Always tie the unused outer pin (Pin 3) directly to the wiper (Pin 2). If the wiper lifts, the current simply flows through the remaining fixed track, limiting the maximum resistance to the pot's rated value (e.g., 10kΩ) instead of spiking to infinity. For more on conditioning analog signals for microcontrollers, see this SparkFun tutorial on voltage dividers.

Practical Wiring for Sensor Modules and Microcontrollers

How you wire the blue trimpot depends entirely on what you are trying to achieve. Here are the two standard configurations you will use on the bench.

Configuration A: Voltage Divider (Analog Sensor Input)

This is how the blue trimpot is wired on 95% of Arduino and ESP32 sensor modules (like photocell or sound detector boards).

• Pin 1 (CCW): Connect to GND (0V).
• Pin 3 (CW): Connect to VCC (3.3V or 5V, matching your microcontroller's logic level).
• Pin 2 (Wiper): Connect to the Analog Input (e.g., A0 on Arduino, GPIO34 on ESP32).

Bench Note: If you are using an ESP32, remember that its ADC is notoriously non-linear at the extremes (near 0V and 3.3V). Keep your voltage divider output between 0.2V and 3.0V for accurate 12-bit readings.

Configuration B: Current Limiting (Rheostat)

Used for adjusting LED brightness or setting the current limit on a bench power supply.

• Pin 1 (CCW): Connect in series with your load (e.g., the anode of an LED).
• Pin 2 (Wiper): Connect to your voltage source.
• Pin 3 (CW): Jumper directly to Pin 2 (Wiper) to prevent open-circuit failures.