A Temperature Controlled Lamp By PIC16F84A Using ds18B20

PIC16F84A was a popular embedded controller in the last decades. It comes with only basic MCU components without ADC/DAC, hardware PWM etc.

Some temperature sensor such as LM35 or PTC have only analog output, need an ADC module of MCU to the convert temperature data.

DS18B20 is a digital temperature sensor, interface to the MCU only one digital pin. But the communication protocol is such complex.

CCS PICC compiler has a built in library for DS1920 digital thermometer.  The ds1920 has a similar data format with DS18B20.

In this case, I use ds18B20 which nearly identical to ds18S20. But ds18B20 has more precise floating point number.

The driver file touch.c is a ready to use library come with CCS PICC after the installation. It has reset(), read(), and write() function to

process the one-wire bus data.

Schematic diagram

PIC16F84A reads the temperature data from ds18B20 one-wire

thermometer, displays the data to the LCD.

The relay controls the ON/OFF lamp from PIN_A0.

The relay works around 30 degree Celsius.

Source Code written in CCS PICC, could be downloaded here:

#include <16F84A.h>
#fuses XT
#use delay(clock=4000000)

#define LCD_ENABLE_PIN  PIN_B3                                       
#define LCD_RS_PIN      PIN_B1                                        
#define LCD_RW_PIN      PIN_B2                                       
#define LCD_DATA4       PIN_B4                                       
#define LCD_DATA5       PIN_B5                                      
#define LCD_DATA6       PIN_B6                                      
#define LCD_DATA7       PIN_B7

#include <lcd.c>
#include <touch.c>
#include <string.h>
#include <stdlib.h>

#define RELAY PIN_A0
#define TEMP 30
void main() {
   byte buffer[2];
   lcd_init();
   set_tris_a(0x00);
   output_a(0x00);
  
   while (TRUE) {
     if(touch_present()) {
        touch_write_byte(0xCC);
        touch_write_byte (0x44);
        output_high(TOUCH_PIN);
        delay_ms(2000);

        touch_present();
        touch_write_byte(0xCC);
        touch_write_byte (0xBE);
        buffer[0] = touch_read_byte();
        buffer[1] = touch_read_byte();
       
        buffer[0]=(buffer[1]<<5)|(buffer[0]>>3);
       
        lcd_gotoxy(1,1);
        LCD_PUTC("TEMPERATURE:");
       
        lcd_gotoxy(1,2);
        printf(LCD_PUTC,"%c",(buffer[1]&0b11111000)?'-':' ');
        if(buffer[1]&0b11111000) buffer[0]=-buffer[0];
        lcd_gotoxy(2,2);
        printf(LCD_PUTC,"%d.%c C",buffer[0]/2,((buffer[0])&0x01)?'5':'0');
        delay_ms (500);
        lcd_putc("          ");
       
        if((buffer[0]/2)>TEMP) output_high(RELAY);
        else output_low(RELAY);
     }
  }
}