Wednesday, 17 July 2013

How to - Sense temperature (LM 35)


        Hey guys, today we are going to look through something that is very common in our life - Temperature. I understand that the surrounding temperature in Malaysia is quite high, probably around 32 - 34 degree celsius due to the hot weather in Malaysia. Have you ever wonder how can you meausre the surrounding temperature ? By guessing it ? Hahaha. Well, let me introduce you to a temperature sensor - LM 35 ( Celsius)

Below are some features of LM 35 ( Celsius):

  • Calibrated directly in ° Celsius (Centigrade)
  •  Linear + 10.0 mV/°C scale factor
  •  0.5°C accuracy guaranteeable (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
Pin description of physical temperature sensor :

Well, for your information, there are 2 types of LM 35 temperature sensor :
  1. Temperature Sensor (Celsius)  
  2. Temperature Sensor (Fahrenheit) 
The price for each LM 35 temperature sensor normally range from RM 6.00 - RM 8.00. This is the prices that I normally seen.

LM 35 is a type of analog sensor. What do you understand by analog sensor ? Analog sensor is sensor which will give analog output. The voltage output range from 0V to 5V instead of just either 0V (LOW) or 5V(HIGH) which a digital sensor does. The voltage output might be for example 2.5V too.

From the features , we know that LM 35 provides "Linear + 10.0 mV/°C scale factor" . This means that for every 10 mV output voltage, it represents 1 °C. So, if the surrounding temperature is 30°C , then the output voltage measured at Vout and GND should give you approximately 300 mV. You can try it !

        I have made a pretty simple project involving the application of temperature sensor - Temperature-Controlled Automatic Fan. My article about that project was featured in Electroschematics. You can have detail information about the project there.

Read more here :
DIY Temperature-Controlled Automatic Fan

The circuit constructed

Hope you enjoy and understand better about LM 35 temperature sensor and looking forward to hear great projects from you guys .

Thank you.