AVR Tutorials
The Best AVR Microcontroller Tutorials on the Web

ATMega16 Microcontroller Digital LM35 LCD Thermometer

The ATMega16 LCD LM35 Digital Thermometer

In this ATMega16 AVR project we will be designing and implementing a Digital Thermometer with the aid of a Atmel AVR ATMega16 microcontroller, a LM35 temperature sensor/transducer and an alphanumeric LCD module.


Note: Although this AVR project was designed around the ATMega16 the project could have utilized another microcontroller such as an ATMega32, etc. The microcontroller must contain an Analog-to-Digital Converter (ADC) though.


ATMega16 LCD Digital Thermometer Operation & Hardware Description
Our LCD Digital Thermometer circuit and C program is given below. When the circuit is powered up the current air temperature will be displayed on the LCD.


The figure below gives the circuit diagram for the ATmega16 LCD Digital Thermometer.

ATMega16 AVR Microcontroller LCD Digital Thermometer Circuit

Important Note: In order for the LM35 LCD Digital Thermometer unit to work correctly the internal oscillator of the ATMega16 AVR microcontroller must be enabled and set to 4MHz.

Software for the ATMega16 LCD Digital Thermometer
Below is the AVR C implementation of the entire code for the ATMega16 based LCD Digital Thermometer. The code was implemented and built using AVR Studio 5. Be reminded that the internal clock of the ATMega16 microcontroller should be enabled and programmed to operate at 4MHz for the AVR C code to operate correctly. A video of the LCD Digital Thermometer in operation is presented at the end of this page.

/*
 * Digital_Thermometer.c
 *
 * Author:  AVR Tutorials
 * Website: AVR-Tutorials.com
 *
 * Written in AVR Studio 5
 * Compiler: AVR GNU C Compiler (GCC)
 */ 
 
#define F_CPU     4000000UL
#include <avr/delay.h>
#include <avr/io.h>
#include <string.h>
#include <avr/interrupt.h>
 
/*Global Variables Declarations*/
 
/*LCD function declarations */
void LCD_send_command(unsigned char cmnd);
void LCD_send_data(unsigned char data);
void LCD_init();
void LCD_goto(unsigned char y, unsigned char x);
void LCD_print(char *string);
 
/*ADC Conversion Complete Interrupt Service Routine (ISR)*/
ISR(ADC_vect);
 
#define LCD_DATA_PORT     PORTB
#define LCD_DATA_DDR      DDRB
#define LCD_DATA_PIN      PINB
 
#define LCD_CNTRL_PORT    PORTC
#define LCD_CNTRL_DDR     DDRC
#define LCD_CNTRL_PIN     PINC
 
#define LCD_RS_PIN                5
#define LCD_RW_PIN                6
#define LCD_ENABLE_PIN    7
#define SET_HOUR          3
#define SET_MINUTE                4
 
int main(void)
{
        unsigned char i; 
 
    LCD_init();
        LCD_goto(1,2);
        LCD_print("Temperature is");
 
 
        LCD_CNTRL_PORT = (1<<SET_HOUR | 1<<SET_MINUTE);
 
        DDRA = 0x00;                     // Configure PortA as input
 
        ADCSRA = 0x8F;                   // Enable the ADC and its interrupt feature
                                        // and set the ACD clock pre-scalar to clk/128
        ADMUX = 0xE0;                    // Select internal 2.56V as Vref, left justify 
                                        // data registers and select ADC0 as input channel 
 
        sei();                           // Enable Global Interrupts
        ADCSRA |= 1<<ADSC;            // Start Conversion
 
        while(1);
}
 
/* This function sends a command 'cmnd' to the LCD module*/
void LCD_send_command(unsigned char cmnd)
{
        LCD_DATA_PORT = cmnd;
        LCD_CNTRL_PORT &= ~(1<<LCD_RW_PIN);
        LCD_CNTRL_PORT &= ~(1<<LCD_RS_PIN);
 
        LCD_CNTRL_PORT |= (1<<LCD_ENABLE_PIN);
        _delay_us(2);
        LCD_CNTRL_PORT &= ~(1<<LCD_ENABLE_PIN);
        _delay_us(100);
}
 
/* This function sends the data 'data' to the LCD module*/
void LCD_send_data(unsigned char data)
{
        LCD_DATA_PORT = data;
        LCD_CNTRL_PORT &= ~(1<<LCD_RW_PIN);
        LCD_CNTRL_PORT |= (1<<LCD_RS_PIN);
 
        LCD_CNTRL_PORT |= (1<<LCD_ENABLE_PIN);
        _delay_us(2);
        LCD_CNTRL_PORT &= ~(1<<LCD_ENABLE_PIN);
        _delay_us(100);
}
 
void LCD_init()
{
        LCD_CNTRL_DDR = 0xFF;
        LCD_CNTRL_PORT = 0x00;
        LCD_DATA_DDR = 0xFF;
        LCD_DATA_PORT = 0x00;
 
        _delay_ms(10);
        LCD_send_command(0x38);
        LCD_send_command(0x0C);
        LCD_send_command(0x01);
        _delay_ms(10);
        LCD_send_command(0x06);
}
 
/* This function moves the cursor the line y column x on the LCD module*/
void LCD_goto(unsigned char y, unsigned char x)
{
        unsigned char firstAddress[] = {0x80,0xC0,0x94,0xD4};
 
        LCD_send_command(firstAddress[y-1] + x-1);
        _delay_ms(10);      
}
 
void LCD_print(char *string)
{
        unsigned char i=0;
 
        while(string[i]!=0)
        {
                LCD_send_data(string[i]);
                i++;
        }
}
 
/*ADC Conversion Complete Interrupt Service Routine (ISR)*/
ISR(ADC_vect)
{     
        char tempC, tempF, display;
        float tempff;
 
        tempC = ADCH;                 // Output ADCH to PortD
        tempff = (float)tempC;
        tempff = (tempff*9)/5 + 32;   
        tempF = tempff;
 
        LCD_goto(2,4);    
        itoa(tempC/10,display,10);
        LCD_print(display);
        itoa(tempC%10,display,10);
        LCD_print(display);
        LCD_send_data(0xDF);
        LCD_print("C   ");
        itoa(tempF/10,display,10);
        LCD_print(display);
        itoa(tempF%10,display,10);
        LCD_print(display);
        LCD_send_data(0xDF);
        LCD_print("F");
        _delay_ms(500);
        ADCSRA |= 1<<ADSC;            // Start Conversion
}

Video demonstrating the ATMega16 LCD Digital Thermometer

AVR Tutorials hopes this AVR project on the ATMega16 LCD LM35 Digital Thermometer was benificial to you and looks forward to your continued visits for all your AVR microcontroller projects needs.