Project Title: Digital Thermometer with LCD Using PIC16F877A

1. Introduction

In this project, you’ll build a digital thermometer using the PIC16F877A microcontroller and the LM35 temperature sensor. The measured temperature will be displayed on a 16×2 LCD in Celsius format.

Real-world applications include:

• Home automation
• Weather monitoring systems
• Environmental control units in HVAC

2. Learning Objectives

Through this project, you will learn to:

• Read analog sensor data using the ADC module of a PIC microcontroller.
• Display real-time data on an LCD.
• Perform voltage-to-temperature conversion based on sensor output.
• Understand embedded C programming using MPLAB X and XC8 compiler.

3. Tools and Components

Microcontroller and Peripherals:

• 1x PIC16F877A Microcontroller
• 1x 16×2 LCD Display
• 1x LM35 Temperature Sensor

Support Components:

• 1x 10kΩ Potentiometer (for LCD contrast)
• 1x 10kΩ Resistor (pull-up for MCLR if needed)
• 1x 20 MHz Crystal Oscillator
• 2x 22pF Ceramic Capacitors

Additional Items:

• Breadboard and jumper wires
• MPLAB X IDE and XC8 Compiler
• PICkit 3/4 Programmer

4. Background and Definitions

PIC16F877A
A popular 40-pin 8-bit microcontroller featuring:

• Multiple I/O ports
• 10-bit ADC with selectable input channels
• Compatible with standard external oscillators

LM35 Sensor
An analog sensor that provides:

• 10mV output per 1°C temperature increase
• Linear voltage-temperature relationship

16×2 LCD Module
A character display module that shows:

• 2 lines of 16 characters each
• Interfaced in either 4-bit or 8-bit mode (this project uses 4-bit)

5. Step-by-Step Guide

Wiring Instructions

LCD Connections (using 4-bit mode):

• VSS → GND
• VDD → +5V
• V0 → Middle pin of potentiometer (contrast adjustment)
• RS → RC0
• RW → GND
• EN → RC1
• D4 → RC2
• D5 → RC3
• D6 → RC4
• D7 → RC5

LM35 Sensor:

• V+ → +5V
• Output → RA0 (Analog channel 0)
• GND → GND

Crystal Oscillator Setup:

• Crystal connected between pins 13 (OSC1) and 14 (OSC2)
• One 22pF capacitor from each pin to ground

Embedded C Code (MPLAB X with XC8 Compiler)

#include <xc.h>
#include <stdio.h>

// Configuration bits
#pragma config FOSC = HS, WDTE = OFF, PWRTE = OFF, BOREN = ON, LVP = OFF, CPD = OFF, WRT = OFF, CP = OFF

#define _XTAL_FREQ 20000000

// LCD control pins
#define RS RC0
#define EN RC1
#define LCD PORTC

void lcd_cmd(char cmd);
void lcd_init();
void lcd_data(char data);
void lcd_print(const char *str);

void ADC_Init();
unsigned int ADC_Read(unsigned char channel);

void main() {
    char buffer[16];
    unsigned int adc_value;
    float temperature;

    TRISA = 0x01;  // RA0 as input (AN0)
    TRISC = 0x00;  // PORTC as output
    ADC_Init();
    lcd_init();

    while (1) {
        adc_value = ADC_Read(0);
        temperature = adc_value * 0.488; // Convert ADC value to Celsius

        lcd_cmd(0x80);
        lcd_print("Temp: ");
        sprintf(buffer, "%.2f C", temperature);
        lcd_print(buffer);

        __delay_ms(1000);
    }
}

void lcd_cmd(char cmd) {
    RS = 0;
    LCD = (LCD & 0x0F) | (cmd & 0xF0);
    EN = 1; __delay_ms(2); EN = 0;
    LCD = (LCD & 0x0F) | ((cmd << 4) & 0xF0);
    EN = 1; __delay_ms(2); EN = 0;
}

void lcd_data(char data) {
    RS = 1;
    LCD = (LCD & 0x0F) | (data & 0xF0);
    EN = 1; __delay_ms(2); EN = 0;
    LCD = (LCD & 0x0F) | ((data << 4) & 0xF0);
    EN = 1; __delay_ms(2); EN = 0;
}

void lcd_init() {
    lcd_cmd(0x02);
    lcd_cmd(0x28);
    lcd_cmd(0x0C);
    lcd_cmd(0x06);
    lcd_cmd(0x01);
}

void lcd_print(const char *str) {
    while (*str) {
        lcd_data(*str++);
    }
}

void ADC_Init() {
    ADCON0 = 0x01; // Channel 0, ADC ON
    ADCON1 = 0xC0; // Right justified
}

unsigned int ADC_Read(unsigned char channel) {
    ADCON0 &= 0xC5;
    ADCON0 |= channel << 3;
    __delay_ms(2);
    GO_nDONE = 1;
    while (GO_nDONE);
    return ((ADRESH << 8) + ADRESL);
}

6. Testing and Debugging Tips

If the LCD does not show any text:

• Adjust the contrast via the potentiometer
• Confirm RS/EN and data pin connections are correct
• Check the initialization sequence in code

If the temperature seems inaccurate:

• Ensure your VDD is a stable 5V
• Confirm the LM35 output is properly routed to RA0
• Recalculate the scaling factor if using a different reference voltage

If the microcontroller is unresponsive:

• Verify crystal oscillator connections and power supply
• Check your programmer’s connection and hex upload

7. Project Extensions and Enhancements

• Add a push-button to toggle between Celsius and Fahrenheit.
• Log the temperature values on an SD card using SPI.
• Use a Bluetooth module (e.g., HC-05) to send data to a mobile app.
• Upgrade to a graphical OLED or TFT for dynamic data visualization.