On the ESP32, some pins are connected to the integrated ADC of the microcontroller. An ADC is an analog to digital converter that returns a digital value proportional to the measured voltage.
On the ESP32, pins 36, 39, 34 and 35 can be analog inputs with MicroPython. The resolution of the measurements is 12 bits, so the measurements are between 0 and 4095.
Unlike the Arduino, the analog inputs on the ESP32 must not exceed a voltage of 3.3V. This could damage or even destroy the inputs of the ADC. It is, therefore, necessary to check that you do not use a supply voltage of 5V to measure the value of a sensor. There are solutions to limit the input voltage of the ADC.
The voltage of analog input is measured using the sub-module
ADC of the
machine . As for PWM, a physical pin is associated with the
from machine import Pin, ADC # Pin definitions adc_pin = Pin(36, mode=Pin.IN) adc = ADC(adc_pin) adc.atten(ADC.ATTN_11DB)
Do not forget to import the ADC sub-module. You will note that for the ESP32, you must also specify attenuation of 11 dB (with
ADC.ATTN_11DB ) to read a voltage over the range of 0 to 3.3V.
You can also create an
ADC by specifying the number of the analog channel you want to use.
from machine import ADC adc = ADC(0) # Select the ADC_0 ()
On the ESP32, the analog channels are assigned to the pins disorderly. It is, therefore, better to use the definition by pin number.
Once you have configured an analog input in MicroPython, you only need to use the function
read() to read the analog value.
from machine import Pin, ADC adc = ADC(Pin(36, mode=Pin.IN)) print(adc.read())
It will be necessary to use a cross product to have the value measured in volt:
We will use PWM and ADC with MicroPython to control the brightness of an external LED.
Electrical schematic :
Remember putting a resistor in series with the LED to prevent it from burning (330 Ω, for example)
To read the position of the potentiometer alone:
from machine import Pin, ADC import time # Create an ADC object linked to pin 36 adc = ADC(Pin(36, mode=Pin.IN)) while True: # Read ADC and convert to voltage val = adc.read() val = val * (3.3 / 4095) print(round(val, 2), "V") # Keep only 2 digits # Wait a bit before taking another reading time.sleep_ms(100)
For reading the position of the potentiometer and changing the brightness:
from machine import Pin, ADC, PWM import time def map(x, in_min, in_max, out_min, out_max): """ return linear interpolation like map() fonction in Arduino""" return (x - in_min) * (out_max - out_min) // (in_max - in_min) + out_min if __name__ == "__main__": # Create a PWM object linked to pin 23 pwm_led = PWM(Pin(23,mode=Pin.OUT)) pwm_led.freq(1_000) # Create an ADC object linked to pin 36 adc = ADC(Pin(36, mode=Pin.IN)) adc.atten(ADC.ATTN_11DB) while True: val = adc.read() pwm_value = map(x=val, in_min=0, in_max=4095, out_min=0,out_max=1023) pwm_led.duty(pwm_value) time.sleep_ms(10)