ESP32 ADC – Read Analog Values with Arduino IDE

Let us learn how to read analog inputs with the ESP32 using Arduino IDE. Analog reading is useful to read values from variable resistors like potentiometers, or analog sensors.

Analog Inputs (ADC)

Reading an analog value with the ESP32 means you can measure varying voltage levels between 0 V and 3.3 V.

The voltage measured is then assigned to a value between 0 and 4095, in which 0 V corresponds to 0, and 3.3 V corresponds to 4095. Any voltage between 0 V and 3.3 V will be given the corresponding value in between.

ADC is Non-linear

Ideally, you would expect a linear behavior when using the ESP32 ADC pins. However, that doesn’t happen. What you’ll get is a behavior as shown in the following chart:

This behavior means that your ESP32 is not able to distinguish 3.3 V from 3.2 V. You’ll get the same value for both voltages: 4095.

The same happens for very low voltage values: for 0 V and 0.1 V you’ll get the same value: 0. You need to keep this in mind when using the ESP32 ADC pins.

analogRead() Function

Reading an analog input with the ESP32 using the Arduino IDE is as simple as using the analogRead() function. It accepts as argument, the GPIO you want to read:

analogRead(GPIO);

The ESP32 supports measurements in 18 different channels. Only 15 are available in the DEVKIT V1 DOIT board (version with 30 GPIOs).

Grab your ESP32 board pinout and locate the ADC pins. These are highlighted with a red border in the figure below.

These analog input pins have 12-bit resolution. This means that when you read an analog input, its range may vary from 0 to 4095.

Other Useful Functions

There are other more advanced functions to use with the ADC pins that can be useful in other projects.

Read Analog Values from a Potentiometer with ESP32

Components Required

• ESP32 DOIT DEVKIT V1 Board 
• Potentiometer
• Breadboard
• Jumper wires

Schematic

Wire a potentiometer to your ESP32. The potentiometer middle pin should be connected to GPIO 34. You can use the following schematic diagram as a reference.

 Code

We’ll program the ESP32 using Arduino IDE, so make sure you have the ESP32 add-on installed before proceeding:

In case you don,t have the Arduino IDE installed install it from here.

// Potentiometer is connected to GPIO 34 (Analog ADC1_CH6) 
const int potPin = 34;
// variable for storing the potentiometer value
int potValue = 0;
void setup() {
  Serial.begin(115200);
  delay(1000);
}
void loop() {
  // Reading potentiometer value
  potValue = analogRead(potPin);
  Serial.println(potValue);
  delay(500);
}

const int potPin = 34;
In the setup(), initialize serial communication at a baud rate of 115200.
Serial.begin(115200);
In the loop(), use the analogRead()function to read the analog input from the potPin.
potValue = analogRead(potPin)
Finally, print the values read from the potentiometer in the serial monitor.
Serial.println(potValue);

The maximum value you’ll get is 4095 and the minimum value is 0.

Wow!! You Learnt It.

In this article, you’ve learned how to read analog inputs using the ESP32 with the Arduino IDE. In summary:

• The ESP32 DEVKIT V1 DOIT board (version with 30 pins) has 15 ADC pins you can use to read analog inputs.
• These pins have a resolution of 12 bits, which means you can get values from 0 to 4095.
• To read a value in the Arduino IDE, you simply use the analogRead() function.
• The ESP32 ADC pins don’t have a linear behavior. You’ll probably won’t be able to distinguish between 0 and 0.1V, or between 3.2 and 3.3V. You need to keep that in mind when using the ADC pins.

Amith G Nair

Experience as a product developer, innovation coach, and electronics lecturer,a seasoned professional driven by passion for designing projects.expertise extends to 3D modelling, hardware designing, and web development using HTML, WordPress, and Django.

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