In this project, we made a temperature-controlled thermometer with LM35 sensor using PIC16F877 microcontroller integration. A / D converter feature of PIC 16F877 was used for thermometer application. The LCD screen is used as the output unit in the circuit. The main feature of the application, however, is to operate the fan or heater depending on the temperature at the temperature values below or above the temperature (20C-25C) in a certain band range.
Circuit and Operation: LM 35 temperature sensor is used for analog input for A / D converter. These processed signals are printed to the output unit LCD as the temperature value.
This value is compared with the previously determined temperature range (room temperature), if the temperature is below the specified temperature values, a voltage of 5V is seen at the end of the C port of the microcontroller (RC6). This voltage value transmits the transistor connected to the RC6 pin and closes the contacts of the transistor-connected relay, and the controller is activated, while the LCD displays the ime cold pin text with the temperature value.
When the temperature value goes above the band values, this time pin 7 of the C port (RC7) shows a 5-volt output, and with the help of the transistor at the output, it closes the contacts of the other relay and the fan is activated. The LCD display also shows ”hot“. If the temperature value is a value in the band, the circuit only serves as a thermometer, no device will operate and the LCD will display ında normal alı with the temperature value.
SCHEMATIC CIRCUIT DIAGRAM:
Print circuit board and top view
When the circuit is viewed, it is seen that very few elements are required. This requires a simple design that is in print mode.