Chapter 8

Until now, Arduino has lived in a binary world.

  • HIGH or LOW

  • ON or OFF

  • Pressed or Released

But the real world is not binary.

Light intensity, temperature, distance, pressure — these things change gradually.
To sense them, Arduino needs to move beyond digital logic.

That’s where analog input comes in.

🌊 What Is an Analog Signal?

An analog signal is a signal that can take many values, not just two.

Examples:

  • brightness of light

  • temperature of a room

  • position of a knob

  • sound amplitude

Instead of asking:

“Is this HIGH or LOW?”

Arduino now asks:

“How much voltage is here?”

🔌 Analog Pins on Arduino

On the Arduino Uno, analog input pins are labeled:

A0, A1, A2, A3, A4, A5

These pins are connected to an internal circuit called the ADC
(Analog-to-Digital Converter).

🧠 What the ADC Actually Does

The ADC:

  • measures the voltage on an analog pin

  • converts it into a number Arduino can understand

On Arduino Uno:

  • input range: 0V to 5V

  • resolution: 10-bit

That means:

0V → 0
5V → 1023

Every voltage in between maps to a value between 0 and 1023.

🔢 analogRead() Basics

To read an analog value we use:

int sensorValue = analogRead(A0);

This returns a number between 0 and 1023,
depending on the voltage present at pin A0.
Similarly, we can obtain inputs from other analog pins!

🧪 Hardware Time: Reading a Potentiometer

Components Required:

  • Breadboard
  • Male to Female Jumper Wires
  • Arduino UNO
  • 10k Potentiometer

A potentiometer is the easiest analog sensor to understand.

It is a variable voltage divider.
Check this article to learn more about potentiometer.

Now,

Connect the three pins of the potentiometer in the given way!


One end → 5V
Other end → GND
Middle pin → A0

Once done, upload the code given below to Arduino.

Code:


void setup() {
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(A0);
  Serial.println(value);
  delay(200);
}

Paste and hit Upload!
Open the serial monitor on the top right corner.

Turn the knob and watch the numbers change.

This is analog input in its purest form.


Try rotating the potentiometer and observe how the analog value changes in the Serial Monitor.

Why didn't we use pinMode() here?

You might be wondering why we didn’t explicitly set pin A0 as INPUT using pinMode().

That’s because analog pins are input-only by default.
When you use analogRead(), Arduino automatically routes that pin to the internal ADC (Analog-to-Digital Converter).

In simple terms:

  • digital pins need direction to be specified
  • analog pins are already meant for reading voltages

So no extra configuration is required here.

🧠 What You Should Notice

  • The values change smoothly

  • Small turns → small number changes

  • Big turns → big number changes

This is fundamentally different from digital input.

⚠️ Important Things to Remember

  • Analog pins do not output voltage (by default)

  • They only measure voltage

  • Input voltage must stay between 0–5V

  • Exceeding this can damage the ADC

This why we require a voltage divider!!

🧰 Common Beginner Mistakes

  • Connecting sensors directly without a voltage divider

  • Expecting analog pins to “output analog voltage”

  • Forgetting to connect GND

  • Confusing analogRead() with PWM

These are normal mistakes. You’re learning how the real world behaves.

Many sensors that you will use will use the ADC logic!

📌 What Comes Next

Now that we can read levels, the next step is to use those levels meaningfully.

👉 Next Chapter — Using Potentiometers & Mapping Values

This is where raw numbers become control.
Next Post Coming Soon!!