ITP Notebook

Lab: Analog Input with an Arduino

September 17, 2020

Physical Computing

Lab Guide

In this lab I learned how to read analog input using an Arduino. I wired two circuits, to digitally control LEDs using variable resistors.

Reading a Potentiometer

For the first circuit, I connected a rotary potentiometer to the A0 pin and a 220Ω resistor in series with an LED to the D9 pin. The potentiometer also needed to be connected to pulldown resistor in series with ground.

The potentiometer and LED connected to the Arduino The potentiometer and LED connected to the Arduino

The following code reads the pot’s value and writes a brightness value to the LED.

const int ledPin = 9;
int analogValue = 0;
int brightness = 0;

void setup() {
  pinMode(ledPin, OUTPUT);

void loop() {
    // read the pot value
    analogValue = analogRead(A0);
    //divide by 4 to fit in a byte
    brightness = analogValue / 4;
    // PWM the LED with the brightness value
    analogWrite(ledPin, brightness);

With the code uploaded, rotating the potentiometer controls the brightness of the LED.

Rotating the potentiometer changes the LED's voltage

Reading Force Sensing Resistors

Next I wired the breadboard to read two Force Sensing Resistors (FSRs) so that each one controls the voltage of an LED. Following the schematic, I connected FSRs to pins A1 and A2, and the LEds to pins 2 and 3.

Both LEDs illuminate faintly by default Both LEDs illuminate faintly by default

I then uploaded the following code. It controls the brightness of the two LEDs by mapping the values coming from the FSRs to the correct range.

const int leftLED = 2;
const int rightLED = 3;
int rightSensorValue = 0;
int leftSensorValue = 0;

void setup() {
  pinMode(leftLED, OUTPUT);
  pinMode(rightLED, OUTPUT);

void loop() {
  rightSensorValue = analogRead(A1);
  // map the sensor value from the input range to the output range (0-255).
  int brightness = map(rightSensorValue, 400, 900, 0, 255);
  analogWrite(leftLED, brightness);  // set the LED brightness with the result

  // same logic for the other FSR
  leftSensorValue = analogRead(A2);
  brightness = map(leftSensorValue, 400, 900, 0, 255);
  analogWrite(rightLED, brightness);

Pressing on the FSRs now changes the voltage of the LEDs.

Pressing on the FSRs changes the LED voltages