analogRead() and ADC conversion in Arduino - Mini Project: Build & Apply

Reading Analog Sensor Values with analogRead()

📖 Scenario: You have a temperature sensor connected to an Arduino analog pin. You want to read the sensor's voltage using the analog-to-digital converter (ADC) and convert it into a digital value.

🎯 Goal: Build a simple Arduino program that reads an analog sensor value using analogRead(), stores it, and prints the digital value to the Serial Monitor.

📋 What You'll Learn

Create a variable to store the analog pin number

Create a variable to store the analog reading

Use analogRead() to read the sensor value

Print the analog reading to the Serial Monitor

💡 Why This Matters

🌍 Real World

Reading analog sensors like temperature, light, or potentiometers is common in electronics projects to get real-world data.

💼 Career

Understanding ADC and analogRead() is essential for embedded systems and hardware interfacing jobs.

1

Set up the analog pin variable

Create an integer variable called sensorPin and set it to A0 to represent the analog pin where the sensor is connected.

Arduino

// Create an integer variable called sensorPin and set it to A0
// Your code here

Hint

Use int sensorPin = A0; to assign the analog pin.

2

Create a variable to store the analog reading

Create an integer variable called sensorValue to store the value read from the analog pin.

Arduino

int sensorPin = A0;
// Create an integer variable called sensorValue
// Your code here

Hint

Initialize sensorValue to 0 before reading the sensor.

3

Read the analog value from the sensor

Inside the loop() function, use analogRead(sensorPin) to read the sensor value and store it in sensorValue.

Arduino

int sensorPin = A0;
int sensorValue = 0;

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

void loop() {
  // Use analogRead to read sensorPin and store in sensorValue
  // Your code here
}

Hint

Use sensorValue = analogRead(sensorPin); inside loop().

4

Print the analog reading to the Serial Monitor

Add a Serial.println(sensorValue); statement inside the loop() function to display the analog reading on the Serial Monitor.

Arduino

int sensorPin = A0;
int sensorValue = 0;

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

void loop() {
  sensorValue = analogRead(sensorPin);
  // Print sensorValue to Serial Monitor
  // Your code here
}

Hint

Use Serial.println(sensorValue); to print the value.

Practice

1. What does the analogRead() function do on an Arduino?

easy

A. It writes a voltage level to an analog pin.

B. It sends a digital signal to an output pin.

C. It resets the Arduino board.

D. It reads an analog voltage and converts it to a number between 0 and 1023.

Solution

1. Step 1: Understand the purpose of analogRead()

   The function analogRead() reads the voltage on an analog pin and converts it to a number.

2. Step 2: Know the range of values returned

   The returned value ranges from 0 (0 volts) to 1023 (maximum reference voltage, usually 5V or 3.3V).

3. Final Answer:

   It reads an analog voltage and converts it to a number between 0 and 1023. -> Option D

4. Quick Check:

   analogRead() returns 0-1023 [OK]

Hint: Remember: analogRead() maps voltage to 0-1023 [OK]

Common Mistakes:

• Thinking analogRead() writes voltage
• Confusing analogRead() with digitalWrite()
• Assuming analogRead() returns voltage directly
• Believing analogRead() resets the board

2. Which of the following is the correct syntax to read an analog value from pin A0?

easy

A. int sensorValue = analogRead(A0);

B. int sensorValue = digitalRead(A0);

C. analogRead(int A0);

D. int sensorValue = analogWrite(A0);

Solution

1. Step 1: Identify the correct function for analog input

   The function to read analog input is analogRead(), not digitalRead() or analogWrite().

2. Step 2: Check the syntax for reading from pin A0

   The correct syntax is int sensorValue = analogRead(A0); which stores the read value in an integer variable.

3. Final Answer:

   int sensorValue = analogRead(A0); -> Option A

4. Quick Check:

   Use analogRead(pin) to read analog input [OK]

Hint: Use analogRead(pin) to get analog input value [OK]

Common Mistakes:

• Using digitalRead() for analog pins
• Calling analogRead() with wrong syntax
• Using analogWrite() instead of analogRead()
• Trying to pass pin as int inside analogRead()

3. What will be the output of this Arduino code snippet if the analog voltage on pin A1 is 2.5V and the reference voltage is 5V?

int sensorValue = analogRead(A1);
Serial.println(sensorValue);

medium

A. 1023

B. 512

C. 256

D. 0

Solution

1. Step 1: Understand the ADC conversion formula

   The analogRead() converts voltage to a value between 0 and 1023 based on the formula: value = (input voltage / reference voltage) * 1023.

2. Step 2: Calculate the expected value for 2.5V input

   value = (2.5 / 5) * 1023 = 0.5 * 1023 = 511.5, which rounds to 512.

3. Final Answer:

   512 -> Option B

4. Quick Check:

   Half of 1023 is about 512 [OK]

Hint: Multiply voltage ratio by 1023 for analogRead() value [OK]

Common Mistakes:

• Using 1023 directly without scaling
• Confusing digitalRead() output with analogRead()
• Rounding errors ignoring half values
• Assuming analogRead() returns voltage in volts

4. Identify the error in this Arduino code that reads an analog value and prints it:

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

void loop() {
  int val = analogRead(0);
  Serial.print(val);
  delay(1000);
}

medium

A. Serial.begin() must be called inside loop(), not setup().

B. delay() cannot be used with Serial.print().

C. analogRead() should use A0 instead of 0 for clarity and correctness.

D. The variable val must be declared as float, not int.

Solution

1. Step 1: Check the analogRead() argument

   Using 0 instead of A0 can work but is discouraged; A0 is the correct constant for analog pin 0.

2. Step 2: Verify other code parts

   Serial.begin() is correctly in setup(), delay() works fine with Serial.print(), and int is suitable for analogRead() values.

3. Final Answer:

   analogRead() should use A0 instead of 0 for clarity and correctness. -> Option C

4. Quick Check:

   Use A0 for analog pin 0 [OK]

Hint: Use A0 constant for analog pin 0 [OK]

Common Mistakes:

• Using numeric 0 instead of A0 for analogRead()
• Moving Serial.begin() to loop() causing repeated starts
• Thinking delay() stops Serial.print()
• Declaring analogRead() result as float unnecessarily

5. You want to measure a sensor voltage that ranges from 0V to 3.3V using Arduino's analogRead() with a 5V reference. How can you correctly convert the analogRead() value to the actual voltage?

hard

A. Voltage = (analogRead() / 1023.0) * 5.0

B. Voltage = (analogRead() / 1023.0) * 3.3

C. Voltage = (analogRead() / 5.0) * 3.3

D. Voltage = analogRead() * 3.3 / 1023

Solution

1. Step 1: Understand the reference voltage and sensor range

   The Arduino ADC uses 5V as reference, so analogRead() maps 0-5V to 0-1023.

2. Step 2: Calculate voltage from analogRead() value

   To get voltage, multiply the fraction (analogRead()/1023) by 5.0 (the reference voltage), not 3.3.

3. Final Answer:

   Voltage = (analogRead() / 1023.0) * 5.0 -> Option A

4. Quick Check:

   Use reference voltage (5V) in conversion formula [OK]

Hint: Multiply analogRead ratio by reference voltage (5V) [OK]

Common Mistakes:

• Using sensor max voltage (3.3V) instead of reference voltage (5V)
• Dividing by 5 instead of 1023
• Multiplying analogRead() directly without division
• Confusing sensor voltage range with ADC reference