Arduino 10K NTC Thermistor: LCD Thermometer Alarm | ShillehTek

Project Overview

Arduino 10K NTC Thermistor LCD Thermometer: Build an Arduino Nano (or UNO-compatible) thermometer using a 10K NTC thermistor, then display live temperature in C and F on a 16x2 LCD with an over-temperature LED and buzzer alarm.

A thermistor is one of the most affordable temperature sensors: its resistance drops as temperature rises. With a simple 10K/10K voltage divider into an Arduino analog pin and the Steinhart-Hart equation, you can get surprisingly accurate readings.

• Time: About 1 hour
• Skill level: Beginner
• What you will build: An LCD thermometer with a high-temperature alarm, built around a 10K NTC thermistor.

Parts List

From ShillehTek

• 10K NTC Thermistor (MF52-103) - the temperature sensor used in the voltage divider.
• Arduino Nano V3 - reads the analog divider voltage and drives the LCD, LEDs, and buzzer (or any Arduino UNO-compatible board).
• LCD1602 16x2 Display Module - displays temperature in C and F.
• Metal Film Resistor Kit - provides the 10K fixed divider resistor and current-limiting resistors for the LEDs.
• KY-006 Passive Piezo Buzzer - audible over-temperature alarm output.
• 830-Point Breadboard and jumper wires - for quick prototyping and wiring.

External

• Green and red LEDs - visual normal and alarm indicators.
• 10K potentiometer - LCD contrast control (to LCD V0).
• 9V battery (optional) - standalone power option.

Note: This build assumes a 5V Arduino and a 10K fixed resistor paired with a 10K NTC thermistor in a voltage divider feeding A0.

Step-by-Step Guide

Step 1 - Understand the Voltage Divider

Goal: Know how a resistor becomes a thermometer.

What to do: Build the sensing circuit using two components in series between 5V and GND: the thermistor on top, a fixed 10K resistor on the bottom, with the junction feeding analog pin A0.

//              Analog pin A0
//                    |
// 5V |-----/\/\/\----+----/\/\/\-----| GND
//           ^                ^
//    10K thermistor     10K resistor

As temperature rises, the NTC resistance drops, the divider voltage shifts, and the ADC reading changes. The code converts that change into degrees.

Expected result: You can explain why A0 voltage tracks temperature.

Step 2 - Wire the Full Circuit

Goal: Divider, LCD, LEDs, and buzzer connected.

What to do: Wire the thermistor divider into A0. Connect the LCD in 4-bit parallel mode with RS to D2, E to D3, and D4 to D7 to Arduino pins D4 to D7 (use the contrast potentiometer on LCD V0). Wire a green LED to D8 and a red LED to D9 through series resistors. Wire the buzzer to D13.

Expected result: A complete breadboard circuit matching the schematic.

Step 3 - Upload the Steinhart-Hart Sketch

Goal: Convert resistance to accurate degrees.

What to do: Upload the sketch below (by Muhammad Ansar / embeddedlab786). It averages 50 ADC samples for stability, computes thermistor resistance, then applies the Steinhart-Hart equation with standard 10K NTC coefficients. Above 100 F, the red LED and buzzer activate; otherwise the green LED stays on.

Code:

#include <LiquidCrystal.h>
LiquidCrystal lcd(2, 3, 4, 5, 6, 7); // Arduino pins to LCD

#define ThermistorPin A0
long ADC_Value;
float R1 = 10000; // fixed divider resistor
float logR2, R2, T;

// Steinhart-Hart coefficients for a 10K NTC
float c1 = 0.001129148, c2 = 0.000234125, c3 = 0.0000000876741;
float temp_c, temp_f;

#define G_led 8
#define R_led 9
#define buzzer 13

void setup() {
  pinMode(ThermistorPin, INPUT);
  pinMode(R_led, OUTPUT);
  pinMode(G_led, OUTPUT);
  pinMode(buzzer, OUTPUT);

  lcd.begin(16, 2);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("   Welcome To   ");
  lcd.setCursor(0, 1);
  lcd.print("Temperature NTC");
  delay(2000);
  lcd.clear();
}

void loop() {
  ADC_Value = 0;
  for (int i = 0; i < 50; i++) {   // average 50 samples
    ADC_Value = ADC_Value + analogRead(ThermistorPin);
    delay(1);
  }
  ADC_Value = ADC_Value / 50;

  R2 = R1 * (1023.0 / (float)ADC_Value - 1.0); // thermistor resistance
  logR2 = log(R2);
  temp_c = (1.0 / (c1 + c2*logR2 + c3*logR2*logR2*logR2)); // Kelvin
  temp_c = temp_c - 273.15;                    // to Celsius
  temp_f = (temp_c * 9.0) / 5.0 + 32.0;        // to Fahrenheit

  lcd.setCursor(0, 0);
  lcd.print("  Temperature   ");
  lcd.setCursor(0, 1);
  lcd.print(temp_c, 1);
  lcd.write(0xdf); // degree symbol
  lcd.print("C  ");
  lcd.setCursor(9, 1);
  lcd.print(temp_f, 1);
  lcd.write(0xdf);
  lcd.print("F  ");

  if (temp_f > 100) {
    digitalWrite(buzzer, HIGH);
    digitalWrite(G_led, LOW);
    digitalWrite(R_led, HIGH);
    delay(300);
  } else {
    digitalWrite(G_led, HIGH);
    digitalWrite(R_led, LOW);
  }

  digitalWrite(buzzer, LOW);
  delay(500);
}

Expected result: A welcome screen, then live C and F readings updating about twice per second.

Step 4 - Test the Alarm

Goal: Verify the whole chain.

What to do: Pinch the thermistor between your fingers and watch the temperature climb. Warm it past 100 F (37.8 C) and the red LED should light with the buzzer chirping. Let it cool and the green LED returns. Adjust the temp_f > 100 threshold for your application.

Expected result: Accurate readings and a working over-temperature alarm.

Conclusion

You turned a 10K NTC thermistor into a calibrated Arduino LCD thermometer using a simple divider and the Steinhart-Hart equation, complete with visual and audible alarms. This same pattern is useful for enclosures, incubators, aquariums, and other low-cost temperature monitoring projects.

Reference credit: photos and original guide credited to Hackster.io and Muhammad Ansar (embeddedlab786).

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