Temperature, humidity and air

NTC thermistor 10k with ESP32

Copied thermistor code often gives a temperature that moves the wrong way, and the reason is the wiring. The usual tutorial formula assumes the NTC sits on the ground side of the divider, while the tutorial's own diagram may put it on the 3.3 V side. This page uses one layout: 10 kΩ from 3V3 to the ADC pin, and the NTC from that pin to ground. Then Rt = R × V / (Vs − V).

Temperature comes from the Beta equation, using 10 kΩ at 25 °C and a Beta value such as 3950 from the part's data. Check your part's values, because 3950 is common but not universal. The NTC gets less resistive when hot, so in this layout the pin voltage falls as temperature rises. Use analogReadMilliVolts, not a raw count against 4096. The arduino-esp32 call applies calibration, and the raw value is less accurate on some chips.

A thermistor is cheap, small and fits in a probe, but accuracy depends on the ESP32 ADC, the fixed resistor and the actual 3.3 V rail. Do not expect tenths of a degree without calibration. Take a few readings and average them. Current through the divider heats the NTC very slightly, which matters only for precise work. For long wires, or where you want a digital value, a DS18B20 is easier. Use an ADC1 pin, because ADC2 conflicts with WiFi. LCD Ultra Pro can read an analog pin and scale it to a range, which gives a rough readout over a small span. The curve is not linear, so accurate degrees need the code below.

const int ADC_PIN = 4;
const float VS = 3300, R_FIXED = 10000, R0 = 10000, BETA = 3950;

float readCelsius() {
  long sum = 0;
  for (int i = 0; i < 32; i++) sum += analogReadMilliVolts(ADC_PIN);
  float mv = sum / 32.0;
  float rt = R_FIXED * mv / (VS - mv);     // NTC on the ground side
  return 1.0 / (log(rt / R0) / BETA + 1.0 / 298.15) - 273.15;
}

void setup() {
  Serial.begin(115200);
}

void loop() {
  Serial.printf("%.1f C\n", readCelsius());
  delay(1000);
}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.