The LM35D is a precision integrated-circuit temperature sensor whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. Unlike thermistors which require complex linearization formulas, the LM35D is factory-calibrated and provides a straightforward output of 10mV per degree Celsius. This makes it incredibly easy to interface with the Analog-to-Digital Converter (ADC) of any microcontroller.

Key Features

• Linear Scale Factor: Direct output of +10.0 mV/°C, making calculations simple ( 250mV = 25°C).
• High Precision: Guaranteed accuracy of 0.5°C at room temperature.
• Low Self-Heating: Draws very low current (approx. $60\mu A$), ensuring the sensor doesn't heat itself up and skew readings.
• No Calibration Needed: Comes pre-calibrated from the factory for the Celsius scale.
• Wide Voltage Range: Operates reliably on standard 4V to 30V power supplies.

Pin Configuration (Module Version)

Most LM35D modules come with a 3-pin header for easy "Plug and Play" connectivity:

1. VCC: Power Supply (4V - 30V).
2. OUT: Analog Output Signal (Connect to MCU Analog Pin).
3. GND: Ground.

Calculation Formula

To convert the analog voltage read by your microcontroller into a temperature reading, use the following logic:

Temperature (°C) = V_out (in mV 10)

Example: If your Arduino reads an input of 220mV, the temperature is 22°C.

 
Common Applications

• Ambient Room Monitoring: Simple thermometers for home automation.
• Overheat Protection: Monitoring heat sinks in power supplies or motor drivers.
• Incubators & Greenhouses: Maintaining stable temperatures for plants or biological samples.
• Battery Management: Monitoring temperature during charging cycles.

Pro Tips for Accuracy

• Stable Power: Use a stable 5V reference. If your power supply fluctuates, your analog readings will also drift.