Let's now test how to Input analog value signals.

There are in total 18 x 12 bits ADC input channels, versus only 1 X 10bits ADC on NodeMCU.

GPIO ADC Channel

• GPIO 0 ==> ADC2_CH1

• GPIO 2 ==> ADC2_CH2

• GPIO 4 ==> ADC2_CH0

• GPIO 12 => ADC2_CH5

• GPIO 13 => ADC2_CH4

• GPIO 14 => ADC2_CH6

• GPIO 15 => ADC2_CH3

• GPIO 25 => ADC2_CH8

• GPIO 26 => ADC2_CH9

• GPIO 27 => ADC2_CH7

• GPIO 32 => ADC1_CH4

• GPIO 33 => ADC1_CH5

• GPIO 34 => ADC1_CH6

• GPIO 35 => ADC1_CH7

• GPIO 36 => ADC1_CH0

• GPIO 37 => ADC1_CH1

• GPIO 38 => ADC1_CH2

• GPIO 39 => ADC1_CH3

To read the analog input, you will the same as have done with Arduino and ESP8266:

int analog_value = analogRead(36);

It's very important to note that, the ESP32 ADCs have 12bits of resolution (versus 10bits on ESP8266 and Arduino), so the total range of ADCs reading go to 4,095 (instead 1,027 on Arduinos and ESP8266) when a maximum of 3.3V is applied to its inputs.

For input, let's use a 10K ohm potentiometer, connecting it from 3.3V and GND. Let's use its variable output to be the input for ESP32 ADC pins. The Above diagram shows the potentiometer connected to GPIO 36 that is the ADC1 Channel 0. Try also other inputs on your board.

Run the simple code below:

/****************************************************** 
* ESP32 Analog Input Test 
* Analog Input: ADC_1_0 pin ==> GPIO36 (VP).
* 
* MJRoBot.org 6Sept17
*****************************************************/
//Analog Input
#define ANALOG_PIN_0 36
int analog_value = 0;

void setup()
{
  Serial.begin(115200);
  delay(1000); // give me time to bring up serial monitor
  Serial.println("ESP32 Analog IN Test");
}

void loop()
{
  analog_value = analogRead(ANALOG_PIN_0);
  Serial.println(analog_value);
  delay(500);
}