How to Use LM335 Temp Sensor: Examples, Pinouts, and Specs

The LM335 is a precision temperature sensor designed to provide an output voltage directly proportional to the absolute temperature in Kelvin. With its linear output and high accuracy, the LM335 is ideal for a variety of temperature measurement and control applications. It operates over a wide temperature range, making it suitable for industrial, scientific, and consumer applications.

• HVAC systems for temperature monitoring and control
• Weather stations and environmental monitoring
• Industrial process control
• Consumer electronics requiring temperature sensing
• Laboratory-grade temperature measurement systems

The LM335 is a versatile and reliable temperature sensor. Below are its key technical specifications:

The LM335 is typically available in a 3-pin TO-92 package. Below is the pinout description:

The LM335 is straightforward to use in temperature sensing applications. Below are the steps and considerations for integrating it into a circuit:

1. Power Supply: Connect the V+ pin to a DC voltage source (2.7V to 40V). Ensure the supply voltage is stable.
2. Ground: Connect the GND pin to the ground of the circuit.
3. Output: The VOUT pin provides a voltage proportional to the temperature in Kelvin. For example, at 25°C (298K), the output voltage will be approximately 2.98V.

• To improve accuracy, you can calibrate the LM335 using an external resistor (typically a 5kΩ potentiometer) connected between the VOUT pin and the V+ pin. Adjust the potentiometer to fine-tune the output voltage.

• Bypass Capacitor: Place a 0.1µF capacitor between V+ and GND to filter noise and improve stability.
• Temperature Conversion: The LM335 outputs temperature in Kelvin. To convert to Celsius, use the formula: [ T_{Celsius} = V_{OUT} - 2.73 ] where ( V_{OUT} ) is in volts.
• Arduino Compatibility: The LM335 can be interfaced with an Arduino for digital temperature monitoring.

Below is an example of how to connect the LM335 to an Arduino UNO and read temperature data:

• Connect the V+ pin of the LM335 to the 5V pin of the Arduino.
• Connect the GND pin of the LM335 to the GND pin of the Arduino.
• Connect the VOUT pin of the LM335 to an analog input pin (e.g., A0) on the Arduino.

// LM335 Temperature Sensor Example
// Reads temperature in Kelvin and converts to Celsius

const int sensorPin = A0; // LM335 output connected to analog pin A0
const float voltageRef = 5.0; // Reference voltage of Arduino (5V)

void setup() {
  Serial.begin(9600); // Initialize serial communication
}

void loop() {
  int sensorValue = analogRead(sensorPin); // Read analog value from LM335
  float voltage = (sensorValue / 1023.0) * voltageRef; // Convert to voltage
  float temperatureK = voltage * 100.0; // Convert voltage to Kelvin
  float temperatureC = temperatureK - 273.15; // Convert Kelvin to Celsius

  // Print temperature readings to Serial Monitor
  Serial.print("Temperature in Kelvin: ");
  Serial.print(temperatureK);
  Serial.print(" K, Celsius: ");
  Serial.print(temperatureC);
  Serial.println(" °C");

  delay(1000); // Wait 1 second before next reading
}

• Avoid exposing the LM335 to temperatures beyond its specified range (-40°C to +100°C).
• Use proper decoupling capacitors to minimize noise in the output signal.
• For long-distance connections, shielded cables are recommended to reduce interference.

1. No Output Voltage:

   • Check the power supply connections and ensure the input voltage is within the specified range.
   • Verify that the GND pin is properly connected to the circuit ground.

2. Inaccurate Temperature Readings:

   • Ensure the sensor is calibrated using an external resistor.
   • Check for noise in the power supply and add a bypass capacitor if necessary.
   • Verify that the sensor is not exposed to rapid temperature changes or external heat sources.

3. Fluctuating Output:

   • Add a 0.1µF capacitor between V+ and GND to stabilize the output.
   • Ensure the sensor is not placed near high-frequency noise sources.

Q: Can the LM335 measure negative temperatures?
A: Yes, the LM335 can measure temperatures below 0°C. The output voltage will still be proportional to the absolute temperature in Kelvin.

Q: How do I convert the output voltage to Fahrenheit?
A: First, convert the voltage to Celsius using the formula ( T_{Celsius} = V_{OUT} - 2.73 ). Then, convert Celsius to Fahrenheit using ( T_{Fahrenheit} = (T_{Celsius} \times 9/5) + 32 ).

Q: Can I use the LM335 with a 3.3V microcontroller?
A: Yes, the LM335 can operate with a supply voltage as low as 2.7V, making it compatible with 3.3V systems.

Q: Is the LM335 waterproof?
A: No, the LM335 is not waterproof. If you need to use it in wet environments, consider encasing it in a waterproof housing.

By following this documentation, you can effectively integrate the LM335 temperature sensor into your projects and achieve accurate temperature measurements.