PIC Microcontroller-Based Temperature Monitoring System

Overview

This project involves using a PIC16F877A microcontroller to read temperature data from an LM35 temperature sensor and display it on a 16×2 LCD. Such a system is useful in applications like home automation, industrial temperature monitoring, and weather stations.

Learning Objectives

• Understand how to interface an LM35 temperature sensor with a PIC microcontroller.
• Learn to display temperature readings on an LCD (HD44780 controller).
• Implement ADC (Analog-to-Digital Conversion) on the PIC16F877A.
• Develop C programming skills using MPLAB X IDE and XC8 compiler.
• Debug and troubleshoot microcontroller interfacing issues.

Required Tools and Components

Hardware:

• PIC16F877A Microcontroller
• LM35 Temperature Sensor
• 16×2 LCD Display (HD44780-compatible)
• 10kΩ Potentiometer (for LCD contrast adjustment)
• 4.7kΩ & 330Ω Resistors
• 22pF & 100nF Capacitors
• 20MHz Crystal Oscillator
• Breadboard & Jumper Wires
• 12V DC Adapter or Battery
• IC7805 Voltage Regulator

Software:

• MPLAB X IDE
• XC8 Compiler
• Proteus (for simulation, optional)

Background Information

LM35 Temperature Sensor

The LM35 outputs an analog voltage proportional to temperature. The output voltage follows the formula:

T (°C) = V_out × 100

Since LM35 provides 10mV per °C, a temperature of 30°C will result in 0.30V at the sensor output.

ADC in PIC16F877A

The PIC16F877A has a 10-bit ADC that converts the analog voltage to a digital value between 0 and 1023. The conversion formula is:

Digital Value = (V_in / V_ref) × 1023

With a V_ref of 5V, each ADC step represents 4.88mV.

Circuit Connections

1. LM35 Output connects to AN0 (RA0) of the PIC16F877A.
2. LCD Pins:
   • RS → RD0 (Register Select)
   • RW → RD1 (Read/Write, set to 0 for write)
   • E → RD2 (Enable)
   • D4-D7 → RD4-RD7 (4-bit data mode)
3. Oscillator: A 20MHz crystal connects to pins 13 and 14.
4. Power Supply: The microcontroller operates on +5V, regulated using an IC7805.

Source Code (XC8 for MPLAB X)

Below is the C program to read temperature from the LM35 and display it on an LCD.

#include <xc.h>
#include <stdio.h>
#define _XTAL_FREQ 20000000  // 20MHz Clock Frequency

// CONFIGURATION BITS
#pragma config FOSC = HS     // High-speed Oscillator
#pragma config WDTE = OFF    // Watchdog Timer disabled
#pragma config PWRTE = OFF   // Power-up Timer disabled
#pragma config BOREN = ON    // Brown-out Reset enabled
#pragma config LVP = OFF     // Low Voltage Programming disabled

// Function prototypes
void ADC_Init();
unsigned int ADC_Read(unsigned char);
void LCD_Init();
void LCD_Command(unsigned char);
void LCD_Char(char);
void LCD_String(const char*);
void LCD_Clear();

void main() {
    float temp;
    char buffer[16];

    ADC_Init();  // Initialize ADC
    LCD_Init();  // Initialize LCD
    
    while(1) {
        unsigned int adc_value = ADC_Read(0);  // Read from AN0 (RA0)
        temp = (adc_value * 4.88) / 10.0;  // Convert ADC value to temperature
        sprintf(buffer, "Temp: %.2f C", temp);

        LCD_Clear();
        LCD_String(buffer);
        __delay_ms(1000);
    }
}

// ADC Initialization
void ADC_Init() {
    ADCON0 = 0x41;  // ADC ON, Select AN0 (RA0)
    ADCON1 = 0x80;  // Right justified result, Vref = VDD
}

// Read ADC value from given channel
unsigned int ADC_Read(unsigned char channel) {
    ADCON0 &= 0xC5;  // Clear channel selection bits
    ADCON0 |= (channel << 3);  // Select channel
    __delay_ms(2);  // Acquisition time
    GO_nDONE = 1;  // Start conversion
    while(GO_nDONE);  // Wait for conversion to complete
    return ((ADRESH << 8) + ADRESL);  // Return 10-bit result
}

// LCD Functions
void LCD_Init() { /* LCD initialization sequence */ }
void LCD_Command(unsigned char cmd) { /* Send command to LCD */ }
void LCD_Char(char data) { /* Send character to LCD */ }
void LCD_String(const char* str) { /* Send string to LCD */ }
void LCD_Clear() { LCD_Command(0x01); }

Testing and Troubleshooting

Common Issues and Solutions:

• LCD displays garbage characters: Verify wiring and ensure proper initialization.
• LCD not turning on: Adjust the 10kΩ potentiometer for contrast.
• Temperature always reads 0°C: Check ADC configuration.
• Display flickers: Add a 1-second delay after updating the LCD.
• Incorrect temperature readings: Verify the conversion formula (ADC * 4.88) / 10.

Extensions & Improvements

• Add a Buzzer: Sound an alarm when temperature exceeds a threshold.
• Use EEPROM Storage: Store max/min temperature values.
• Wireless Transmission: Send temperature data via Bluetooth (HC-05) or WiFi (ESP8266).
• Upgrade Display: Use an OLED display instead of a 16×2 LCD.

This project is an excellent introduction to PIC microcontrollers, ADC, and LCD interfacing, offering practical applications in real-world scenarios. Let me know if you need additional details or modifications!