When I read the analogue voltage with code written in the Arduino IDE (using ESP32 Board v1.0.6) I get a reasonable result, but when I attempt to do the same thing in MicroPython (using UIFlow_StickC_Plus-v1.9.3-plus.bin) with the same circuit I get a value of 0.

Example output:

           Aref   width  val     V
Arduino:  3.30V 4095.00 1840 1.48V 
MicroPy:  3.30V 4095.00    0 0.00V

In both instances I have attempted to set the appropriate width and attenuation for the ADC, and to set shared pin 25 to be floating.

Can anyone suggest what might be the fault in my MicroPython code?

Arduino IDE code:

void setup() {
  Serial.begin(9600);
  analogReadResolution(12);
  analogSetWidth(12);
  analogSetAttenuation(ADC_11db);
}

void loop() {
  float adcVoltage = 3.3;
  float adcMax = 4095.0;
  int value = analogRead(36);
  float voltage = value * (adcVoltage / adcMax);
  Serial.print(adcVoltage);
  Serial.print("V ");
  Serial.print(adcMax);
  Serial.print(" ");
  Serial.print(value);
  Serial.print(" ");
  Serial.print(voltage);
  Serial.print("V ");
  Serial.println("");
  delay(500);
}

Micropython code:

import time
from machine import Pin, ADC


def main():
    Pin(25, mode=Pin.IN, pull=None)
    adc = ADC(Pin(36, mode=Pin.IN))

    adc.atten(ADC.ATTN_11DB)
    adc.width(ADC.WIDTH_12BIT)

    adc_voltage = 3.3
    adc_max = 4095.0

    while True:
        value = adc.read()
        voltage = value * (adc_voltage / adc_max)
        print("%4.2fV %7.2f %d %4.2fV" % (
            adc_voltage, adc_max, value, voltage))
        time.sleep(0.5)


main()