What is a potentiometer? How a knob talks to your Arduino

#What it is

A potentiometer ("pot" for short) is a resistor with a sliding contact you move by turning a knob. It has three legs. Put 5 V and GND on the two outer legs, and the middle leg — the wiper — gives any voltage in between, depending on where the knob is. Read that voltage on an analog pin and your Arduino knows the knob's position. See it in 3D.

#How it works inside

Inside is a curved track of resistive material, 10 kΩ from one end to the other, joined to the two outer legs. A small metal brush, joined to the middle leg, slides along the track as you turn the knob (through about 270°).

The brush splits the track into two parts, and together they form a voltage divider: the wiper gets a share of the 5 V that matches how far along the track it is.

The whole track is always between 5V and GND, so a small current flows through it all the time: 5 V ÷ 10,000 Ω = 0.5 mA. That is tiny — safe even if you turn the knob all the way.

#The pins

Which outer leg gets 5V and which gets GND only decides the direction: swap them and turning right makes the number go down instead of up.

#How to wire it to an Arduino

This is the wiring of the potentiometer project:

1. Push the pot into the breadboard, each leg in its own row.
2. 5V → the first outer leg.
3. The middle leg → A0.
4. The other outer leg → GND.
5. To see the result: pin 9 (a ~ PWM pin) → a yellow LED's long leg, its short leg → a 220 Ω resistor → GND.

#Example code

The exact code of the knob project:

const int KNOB = A0;
const int LED = 9;   // a ~ pin: it can dim

void setup() {
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(KNOB);                // 0 … 1023
  int brightness = map(reading, 0, 1023, 0, 255); // 0 … 255
  analogWrite(LED, brightness);
  Serial.print("knob ");
  Serial.print(reading);
  Serial.print("  ->  LED ");
  Serial.println(brightness);
  delay(100);
}

• analogRead(KNOB) measures the wiper's voltage and gives 0 (0 V) to 1023 (5 V).
• map(reading, 0, 1023, 0, 255) scales that range to the one analogWrite() wants.
• analogWrite(LED, brightness) dims the LED with PWM — read PWM explained.

Play in 3DRun the code · press the parts · turn it around

#Common mistakes

• The middle leg on 5V or GND. The reading is stuck at 1023 or 0. The wiper must go to the analog pin.
• Reading a digital pin. analogRead() only works on A0–A5.
• Dimming on a pin without ~. analogWrite() on pin 7 or 13 is only fully on or off. Use 3, 5, 6, 9, 10 or 11.
• Numbers jump by one or two. Normal — tiny noise. Ignore small changes, or average a few readings.

#Check yourself

#Questions people ask

#What does a potentiometer do in an Arduino project?

It turns a knob position into a voltage between 0 and 5 V. analogRead() turns that into 0–1023, which you can use to set brightness, speed, an angle or a threshold.

#What value potentiometer should I use with Arduino?

10 kΩ is the standard choice. Anything from about 1 kΩ to 100 kΩ works; very small values waste current and very large ones give noisier readings.

#Why does my potentiometer only work in half the turn, or jump?

Usually a loose leg on the breadboard, or the wiper wired to an outer pin. Push all three legs in firmly and check that the middle one goes to A0.

#Is a potentiometer the same as a variable resistor?

Almost. A potentiometer has three legs and gives a voltage; if you use only the wiper and one outer leg, it becomes a variable resistor (sometimes called a rheostat).

#Where it is used

Turn it in the potentiometer project, then see the same divider idea at work with light in the night light.

Last updated 2026-10-29