Formally announcing the success of my latest project ‘A DIGITAL THERMOMETER using the famous temperature sensor from National Semiconductor LM35. This is actually a small circuit in which the temperature sensor senses the temperature and the circuit converts the temperature into an equivalent voltage which can be read by connecting the circuit to a Digital Multimeter [DMM].This can sense the room temperature and can be connected to a DMM for the output. This circuit converts temperature into a corresponding voltage i.e., for every degree of the temperature increase the output increases by 1 mV VDC. It uses a 3 lead LM 35 Temperature Sensor.

Connect the output wires to the DMM and set the multimeter for the DC measurement at 200 mV. The output displayed here will be the direct digital conversion of the actual temperature of the room.

This Thermometer finds numerous applications in our daily life, for example, we can measure our body temperature very accurately using this circuit the display reads 37 degree Celsius . Which is more or less perfect, it can sense temperatures form -55 Degree Celsius to +150 Degree Celsius.

Here is the link to the datasheet of the National Semiconductor LM 35 Temperature sensor

A sneak peek into the datasheet of the sensor :


Precision Centigrade Temperature Sensors

General Description

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling. The LM35 does not require any external calibration or trimming to provide typical accuracies of ±1⁄4°C at room temperature and ±3⁄4°C over a full −55 to +150°C temperature range. Low cost is assured by trimming and calibration at the wafer level. The LM35’s low output impedance, linear output, and precise inherent calibration make interfacing to readout or control circuitry especially easy. It can be used with single power supplies, or with plus and minus supplies. As it draws only 60 μA from its supply, it has very low self-heating, less than 0.1°C in still air. The LM35 is rated to operate over a −55° to +150°C temperature range, while the LM35C is rated for a −40° to +110°C range (−10° with improved accuracy). The LM35 series is available packaged in hermetic TO-46 transistor packages, while the LM35C, LM35CA, and LM35D are also available in the plastic TO-92 transistor package. The LM35D is also available in an 8-lead surface mount small outline package and a plastic TO-220 package.


  • Calibrated directly in ° Celsius (Centigrade)
  • Linear + 10.0 mV/°C scale factor
  • 0.5°C accuracy guarantee able (at +25°C)
  • Rated for full −55° to +150°C range
  • Suitable for remote applications
  • Low cost due to wafer-level trimming Operates from 4 to 30 volts
  • Less than 60 μA current drain
  • Low self-heating, 0.08°C in still air
  • Nonlinearity only ±1⁄4°C typical
  • Low impedance output, 0.1 W for 1 mA load


  •  R1        9.1 K Ohm
  • R2        1 K Ohm
  • R3        18 K Ohm
  • D1        IN4148
  • D2        IN4148
  • IC1        LM 35
  • Battery  9 V battery with a battery snapper

DSC01538 1


  1. ranga2004ngarajan

    April 9, 2013 at 9:57 pm

    Nice! Is it possible to find a casing for this?! That will make it complete wont it?!

    • Yes surely there can be a casing made for this, but i wanted to continue with this project more longer in fact i wanted to add a display screen for this, like SSD [Seven Segment Display] so that there is no need to connect the circuit to a Digital Multimeter to read the temperature.

      Once its done, then there can be a casing done for this, just like the way i have created for the LED lamp.

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