Over heat indicator

LM35 are precision integrated circuit senser,whose output voltage is linearly proportional to celsius(centigrade) it provides an output of 10mV/Degree celsius.It has a low cost,low output impedence,linear output.It draws a very small current,of the order,of 70uA from its supply and therefore its self heating is small.

The following circuit is a over heat indicator using LM35.The L.E.D is used to get a direct indication of the temperature level sensed by the LM35.

If the temperature crosses the preset value,the base-emitter voltage of the transister exceeds the limit and transistor starts conducting.The L.E.D gradually begins to illuminate.

Caution must be maintained,not exceed the temperature over 150 degree celsius other wise the sensers may get damaged.