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I have an esp32 WROOM-32 connected to a MQ9 gas sensor to GPIO35. Both are powered separately. measuring the output from the sensor directly using a multi-meter shows a constant reading of 0.145 V but the readings on esp32 shows 3.3V and if fluctuates too much.

The circuit: MQ-9 AO -> voltage divider (using 1k and 2.2k ohm) -> ESP32 (GPIO35)

Sample Code:

void setup() { 
  Serial.begin(9600); 
  analogReadResolution(11);  
  analogSetWidth(11);               // 11Bit resolution
  analogSetAttenuation(ADC_0db);
} 
void loop() { 
 int ADC = analogRead(35);
 float volt = (ADC * 3.3) / 2045;
 Serial.print("Volt : ");
 Serial.println(volt);
 Serial.print("Analog : ");
 Serial.println(ADC);
 Serial.println("");
 delay(1000);
}

Image of the error: Readings and Fluctuation

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  • 2
    please do not post a picture of text ... post the text instead, same as the code Commented Jul 23, 2023 at 14:57
  • the circuit description does not say anything about a ground connection Commented Jul 23, 2023 at 14:59

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