Key Engineering Takeaways
- •A potentiometer is an adjustable voltage divider constructed with a curved resistive carbon track and a sliding wiper contact.
- •Pin 1 connects to VCC (+5V/3.3V), Pin 3 connects to GND (0V), and center Pin 2 (Wiper) outputs a variable voltage.
- •Linear Taper (marked "B", e.g., B10K) changes resistance proportionally with dial angle; used for sensor dials and robotics positions.
- •Logarithmic / Audio Taper (marked "A", e.g., A10K) matches human ear perception; used for audio volume controls.
- •Never connect the wiper directly between power rails without a series load, or turning the dial to the end will create a dead short.
Prerequisites
- • Voltage Dividers and Ohm's Law
Required Hardware / Tools
- • 10kΩ Rotary Potentiometer (B10K)
- • ESP32 / Arduino
- • Breadboard and Jumper Wires
- • Digital Multimeter
Anatomy of a 3-Terminal Potentiometer
A **Potentiometer** (colloquially called a "pot") is a 3-terminal variable resistor.
Inside the metal housing:
- A fixed **resistive carbon/cermet track** stretches between **Outer Pin 1** and **Outer Pin 3** (total resistance, e.g. 10 kΩ, remains fixed).
- A conductive metal **Wiper arm (Center Pin 2)** slides physically along the carbon track as you turn the rotary shaft.
- The wiper divides the track into two variable resistors (R_1 + R_2 = R_total), forming an ideal, mechanically adjustable **Voltage Divider**!
Wiring as an Adjustable Voltage Divider (0V - 5V Output)
To feed a smooth variable voltage into an analog ADC input pin:
1. Connect **Pin 1 to +5.0V (or +3.3V)**.
2. Connect **Pin 3 to Ground (0V)**.
3. Connect **Center Pin 2 (Wiper) to your microcontroller ADC pin** (e.g. Pin A0 on Arduino, or GPIO34 on ESP32).
As you rotate the knob from full counter-clockwise to full clockwise, the voltage on Pin 2 glides smoothly and linearly from **0.00V → +5.00V**!
Potentiometer Tapers: Linear (B) vs Logarithmic / Audio (A)
Always check the letter code stamped on the metal casing before using a potentiometer:
### 1. Linear Taper ("B" Prefix - e.g. B10K):
Resistance changes uniformly and proportionally with rotation (50% rotation = 50% resistance = 2.5V).
- **Use For**: Robotic arm joint angle inputs, speed dials, joystick controls, and lab voltage adjustments.
### 2. Logarithmic / Audio Taper ("A" Prefix - e.g. A10K):
Resistance changes exponentially to match the logarithmic response of the human ear to sound pressure.
- **Use For**: Audio volume knobs and guitar tone controls.
Reading Potentiometer Angle in Microcontroller Firmware
Read the potentiometer voltage and map it directly to a motor speed (0-255) or servo angle (0°-180°):
read_potentiometer.ino
cpp
const int POT_PIN = A0;
void setup() {
Serial.begin(115200);
}
void loop() {
// Read 10-bit raw ADC value (0 to 1023)
int rawADC = analogRead(POT_PIN);
// Calculate real voltage (for 5.0V reference)
float voltage = (rawADC / 1023.0) * 5.0;
// Map to servo angle (0 to 180 degrees)
int servoAngle = map(rawADC, 0, 1023, 0, 180);
Serial.print("Raw: "); Serial.print(rawADC);
Serial.print(" | Voltage: "); Serial.print(voltage, 2);
Serial.print("V | Angle: "); Serial.println(servoAngle);
delay(50);
}Frequently Asked Questions
What is a Trimpot (Trimmer Potentiometer)?
A Trimpot is a miniature potentiometer designed to be adjusted with a tiny screwdriver during factory calibration and then left fixed (e.g., setting LCD contrast or motor driver current limits).
Tags:#Potentiometer#Variable Resistor#ADC#Linear Taper#Audio Taper#Analog Input