The LM35 temperature sensor is a widely trusted choice for anyone who need accurate, linear, and calibration-free temperature measurement. Its simple analog output, low power consumption, and broad operating range make it ideal for embedded, industrial, and environmental applications. This article explores its features, wiring practices, applications, and practical considerations for achieving reliable temperature readings.
What Is the LM35 Temperature Sensor?
The LM35 is a precision analog temperature sensor that outputs a voltage directly proportional to temperature in degrees Celsius. With a fixed scale factor of 10 mV/°C, it provides a simple, linear relationship between temperature and output voltage. Because the LM35 is factory-calibrated and operates with minimal self-heating, it integrates easily into both basic and advanced measurement systems.
LM35 Pinout
| Pin Number | Pin Name | Description |
|---|---|---|
| 1 | Vcc | Supply voltage input, typically +5V |
| 2 | Analog Out | Voltage increases by 10 mV for every 1°C. Outputs 0V at 0°C when using a single supply. Negative temperature output requires a negative supply rail. |
| 3 | Ground | Connect to system ground |
LM35 Sensor Features
| Feature | Description |
|---|---|
| Input Voltage | −2V to 35V (commonly operates at 5V) |
| Temperature Range | −55°C to +150°C |
| Linear Output | 10 mV/°C for straightforward analog-to-digital conversion |
| Accuracy | ±0.5°C at room temperature |
| Current Consumption | Less than 60 µA, ideal for low-power systems |
| Overall Design | Compact, low-cost IC suitable for embedded or remote sensing |
| Available Packages | TO-92, TO-220, TO-CAN, SOIC |
Equivalent or Alternative Temperature Sensors
Here are common LM35 alternatives and how they differ:
• DS18B20 – A digital 1-Wire sensor offering high accuracy, strong noise immunity, and long-cable reliability. Ideal for harsh or electrically noisy environments.
• DS1620 – A digital sensor with built-in thermostat and control features for temperature-regulated systems.
• LM94022 – A low-voltage analog sensor optimized for battery-powered or ultra-low-power applications.
Applications of the LM35 Temperature Sensor
Environmental Monitoring
Used in weather stations, smart agriculture, and indoor climate systems to monitor ambient indoor or outdoor temperature with reliable precision.
Thermal Management
Integrated into electronic circuits to prevent overheating by controlling cooling fans, triggering alarms, or initiating automatic thermal shutdown when temperatures rise beyond safe limits.
Battery Monitoring Systems
Helps ensure safe charging and discharging in lithium-ion and lead-acid batteries by tracking battery temperature and preventing damage caused by thermal runaway.
HVAC Systems
Enhances the efficiency of heating, ventilation, and air-conditioning equipment by providing accurate temperature data for regulating airflow, compressor operation, and energy-saving modes.
Home Automation and IoT Devices
Commonly used in smart thermostats, sensor nodes, and IoT-based temperature monitoring systems due to its simplicity and compatibility with microcontrollers.
Industrial Process Control
Supports temperature regulation in manufacturing, storage facilities, and laboratory environments where stable and accurate temperature measurement is essential.
How to Use the LM35 in Practical Circuits?
The LM35 provides an analog output proportional to temperature and requires only three basic connections:
• Connect +5V to the Vcc pin.
• Connect Ground to the system ground.
• Read the analog voltage from pin 2 using a microcontroller ADC such as Arduino, ESP32, STM32, or PIC.
Output Behavior
• 0°C → 0V
• Each 1°C increase → +10 mV
• Sub-zero measurements require a negative supply rail.
Conversion Formula:
Temperature (°C) = Vout (mV) ÷ 10
Advantages and Limitations of the LM35
Advantages
• No external calibration needed
• Very low power usage (<60 µA)
• High accuracy (±0.5°C at room temperature)
• Linear, predictable output
• Wide range: −55°C to +150°C
Limitations
• Requires an ADC for digital systems
• Can pick up noise over long wires
• Needs extra circuitry for negative temperatures
• Less durable than digital sensors in harsh conditions (e.g., DS18B20)
LM35 vs LM34 Comparison
| Feature | LM35 | LM34 |
|---|---|---|
| Output Scale | 10 mV/°C | 10 mV/°F |
| Measurement Unit | Celsius | Fahrenheit |
| Temperature Range | −55°C to +150°C | −50°F to +300°F |
| Accuracy | ±0.5°C | ±1°F |
| Best Use Cases | Global applications, scientific use, industrial control | U.S.-based consumer devices or systems requiring Fahrenheit output |
Conclusion
The LM35 remains a dependable analog temperature sensor due to its linear output, accuracy, and straightforward integration into electronic systems. Its simplicity makes it a practical choice for many measurement tasks, while an understanding of its wiring needs and limitations ensures optimal performance. When required, several digital and low-voltage alternatives offer enhanced features for specialized applications.
Frequently Asked Questions [FAQ]
How accurate is the LM35 compared to digital temperature sensors?
The LM35 offers ±0.5°C accuracy at room temperature, but digital sensors like the DS18B20 generally provide higher precision and stronger noise immunity. For long-distance wiring or harsh environments, digital sensors typically maintain accuracy better than analog types like the LM35.
Can the LM35 run on 3.3V power instead of 5V?
Yes. The LM35 works with supply voltages as low as 4V for full-range operation, but it can still measure moderate temperatures when powered at 3.3V. The output scale remains 10 mV/°C, but the maximum readable temperature will be limited by the available supply voltage.
Why is my LM35 temperature reading noisy or unstable?
Unstable readings often result from electrical interference or grounding issues. Keep analog lines away from switching components, ensure proper grounding, and use a decoupling capacitor on the supply line.
How do you measure below 0°C with the LM35?
The LM35 needs a negative supply voltage to represent sub-zero temperatures. Without a negative rail, the sensor outputs 0V for any temperature below 0°C.
Can the LM35 be used for surface or liquid temperature measurement?
Yes, if installed correctly. For surfaces, use thermal adhesive or a metal interface to improve heat transfer. For liquids, place the LM35 inside a waterproof metal probe or sealed enclosure to prevent damage while ensuring good thermal conductivity.