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Built-in project · Arduino Uno R3

Knob on A0 dims the LED on pin 9, on an Arduino Uno

A potentiometer across 5 V with its wiper on A0 sets the brightness of an LED on pin 9; the serial monitor shows the reading and the brightness. The whole build, an Arduino Uno and 3 more parts, runs here in your browser on the firmware below; open it in the editor to change the wiring or the code and run it again.

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Knob on A0 dims the LED on pin 9 · Arduino Uno R3live0.000 s 0.00x
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The circuit itself, running here on the simulator. Press what can be pressed; click anything else to open it in the editor.

The code

The firmware exactly as the editor opens it. Change a line there and press Run: it compiles in the browser.

sketch.ino · Arduino Uno R3
// A knob dims an LED: the potentiometer on A0, the LED on pin 9.
//
//   potentiometer: one end -> 5V, the other end -> GND, the middle -> A0
//   pin 9 -> 220 ohm -> LED -> GND
//
// The middle leg (the wiper) slides between the two ends, so A0 sees
// anything from 0 V to 5 V and analogRead() gives 0 to 1023. analogWrite()
// takes 0 to 255, so map() scales one range onto the other.
//
// Drag the knob and watch the LED and the numbers.

const int KNOB = A0;
const int LED = 9;

int shown = -1;

void setup() {
  pinMode(LED, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: knob on A0, LED on pin 9");
}

void loop() {
  int reading = analogRead(KNOB);
  int brightness = map(reading, 0, 1023, 0, 255);
  analogWrite(LED, brightness);
  if (abs(reading - shown) > 8) {
    shown = reading;
    Serial.print("reading ");
    Serial.print(reading);
    Serial.print("  brightness ");
    Serial.println(brightness);
  }
  delay(20);
}

Parts list

5 parts, plus the jumper wires. Every one is in the editor's parts bin.

How it is wired

5 connections, pin by pin, read from the circuit itself. Each line is one set of pins joined together, by a jumper wire or a breadboard strip.

  • Ground: Arduino Uno R3 pin GND; LED, red pin C; Potentiometer pin 3
  • Arduino Uno R3 pin 9; Resistor, 220 Ω pin 1
  • Arduino Uno R3 pin 5V; Potentiometer pin 1
  • Arduino Uno R3 pin A0; Potentiometer pin 2
  • Resistor, 220 Ω pin 2; LED, red pin A

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