5V Pin showing 20V on serial monitor

[jimmy747]

Hello everybody, I just don't get this. I wanted to verify that my TDS sensor was in fact receiving 5V. So. I connected PIN 5V of my ESP32 and ran the following program. Why does it say 20V on the serial monitor? Thank you.

int SensorValue =0;
#define VoltageSensorPin 34

void setup() {
    Serial.begin(9600);
    pinMode(34, INPUT);
  }

void loop() {
  
    SensorValue = analogRead(VoltageSensorPin);

    float voltage = SensorValue * (5.0 / 1023.0);
    Serial.println(voltage);
 
    delay(1000);
  }

[jremington]

@jimmy747

float voltage = SensorValue * (5.0 / 1023.0);

The aboving scaling is completely wrong for the ESP32, which (by the way) has a lousy, nonlinear ADC, not really suitable for use with your TDS meter.

Try something like this, depending on what you have set for the analog reference (default 3.3V, I think):

float voltage = SensorValue * (3.3 / 4096.0);

DO NOT expose any I/O pins to 5V! Use a 2:1 voltage divider to measure 5V (2 10K resistors in series). You may already have trashed the ADC input.

[jimmy747]

oh crap I hope not. ok thank you.