This circuit measures temperature in Celsius and displays it on an alphanumeric LCD. When temperature rise to 40C an alarm is activated and the electromechanical 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. Key '4' is used to turn on or off the buzzer alarm.
The MCU is the ATMEL AT89C51. The LM35 is an TO-92 package temperature sensor. It senses heat from 0C to 100C. The output provides 10mV/C. We use the simple analog to digital converter, ADC0804 to convert the analog signal to digital data. The 8-bit digital data is tied to PORT1. This data is processed by microcontroller and the temperature is displayed on lcd connected to PORT2. The control pins of lcd are connected to PORT0. Some bits of the PORT0 also control the relays and buzzer. The ULN2003 chip is used to drive the relays. Pin 1 to 7 are the inputs and 10 to 16 are respective outputs. Pin 8 is ground and pin 9 is connected to the output of 7808 voltage regulator. The 7805 voltage regulator drives rest of the circuit. I used a standard buzzer driven by LM555 timer/oscillator chip. The 555 circuit is a multivibrator having output for driving the buzzer. We may use any IR receiver module and connect the output to pin 10 of microcontroller. The relay connected to pin 13 of ULN2003 turns on when temperature rises above 40C.
You may download all files in zip format. The file contains the images of completed project, hex file, circuit diagram and pcb file.
Source
You may download all files in zip format. The file contains the images of completed project, hex file, circuit diagram and pcb file.
Source