sensors - ESP32 Analog to Digital ADC

Question

I have a humidity analog sensor that I am trying to read. The sensor outputs a 4-20 mA signal. I converted it into a 0 - 3.3V potential with a 165 Ohm resistor.

When I measure the voltage across the resistors with a multimeter, I get the correct values. I get a voltage of around 2.9V which corresponds to about 87 % humidity which seems to be correct.

However the values of ADC are haywire. I get values between 2500 to 4095, which correspond to between 61 % and 100 % humidity. The sensor is quite accurate so its not a problem with the sensor. I am using ADC on pin 25.

My circuit is shown as an attachment. I have also attached the values of ADC measured.

#include <Arduino.h>
// Potentiometer is connected to GPIO 34 (Analog ADC1_CH6) 
const int Pin = GPIO_NUM_34;
    
void setup() {
  Serial.begin(115200);
  pinMode(Pin, ANALOG);
  delay(1000);
  analogSetAttenuation(ADC_11db);
}
    
void loop() {
  int data = analogRead(Pin);
  double vol = (data * 3.3) / 4095;
  Serial.print(data);
  Serial.print("");
  Serial.print(vol);
  Serial.print("
");
    
  delay(300);
}

question from:https://stackoverflow.com/questions/65901942/esp32-analog-to-digital-adc

Answer 1

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