LM35 Sensor Heater Control PIC16F877 Thermometer

In this project, we made a temperature-controlled thermometer using the PIC16F877 microcontroller IC. The A/D converter feature of the PIC 16F877 was used for the thermometer application. LCD screen is used as the output unit in the circuit. But the main feature of the application is to operate the fan or heater connected to the outputs according to the temperature value at the temperature values below or above the temperature in a certain band range (20C-25C).

Circuit and Operation: The LM35 temperature sensor is used for the analog input required for the A/D converter. The analog signals coming from the LM 35 temperature sensor are converted into digital signals by the A/D converter and can be processed by the microcontroller.

These processed signals are written to the LCD, which is the output unit, as a temperature value.

This value is compared with the previously determined temperature range (room temperature).

This voltage value turns the transistor connected to the RC6 pin into conduction, closes the contacts of the relay connected to the transistor, and the heater becomes active, while the “cold” text is observed on the LCD screen along with the temperature value.

When the temperature value rises above the band values, this time pin 7 (RC7) of the C port shows a 5 volt output and with the help of the transistor in its output, the contacts of the other relay are closed and the fan becomes active. On the LCD screen, “hot” text is seen.

If the temperature value is in the band gap, the circuit acts only as a thermometer, no device works, and “normal” is observed on the LCD along with the temperature value.

LM35 Thermometer PCB Schematic

PIC16F877 Thermometer pic assembly asm and hex code > authors: Abdülaziz Pekdoğan, Murat Denli