This circuit measures temperature in Celsius scale and displays it on an alphanumeric LCD screen. When temperature rise to 40 C an alarm is activated and at the same time a relay is also activated which drives a fan to keep the temperature at a level.
Another feature of this circuit is that you can use the keys “1,2,3,4” of a Philips TV IR remote to turn on or off three relays, The key ‘4’ is used to turn on or off the over temperature alarm. Hardware The brain of this circuit is AT89C51 microcontroller. LM35 is a 3 pin chip which is easily available in TO-92 package. LM35 can sense temperature from 0 C to 100 C but it gives analogue output the microcontroller does not understand analogue data, so ADC0804 (analogue to digital converter) is used to convert it to digital form. This digital data is given to port 1 of microcontroller.This data is processed by microcontroller and temperature is displayed on lcd connected to port 2.The control pins of lcd are connected to port 0. port 0 also controls the relays and alarm.
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