PIC16F887 DHT-11 LCD Example Using XC8

DHT11 converts the surrounding temperature and humidity to serial digital data for any micro-processor. It uses only one serial data wire. It able to convert between 0 and 50 degree Celsius in temperature, and 0 to 90RH for humidity. It's suitable for air conditioning system, agricultural application, etc.

DHT-11 Sensor

Prototyping Board

It contains 5 bytes (40 bits) of digital data. They are 1 byte of humidity, 1 byte of temperature, and 1 byte of check sum. For more information about decoding its data byte please check this post.

DTH-11 Sensor

 

TC1604A-01 16x4 Character LCD Module

In this example, I use an 8-bit PIC micro-controller PIC16F887, a DHT-11 sensor module, and a 16x2 character LCD to read and display the environmental data. I use the Microchip MPLABX IDE v6.15 and its XC8 C compiler v2.36 (free version).

/*
 * File:   main.c
 * Author: Admin
 *
 * Created on December 26, 2023, 9:03 PM
 * PIC16F887 DHT-11 Sensor and LCD Example
 * MPLABX IDE v6.15 XC8 v2.36
 */
 
#include <xc.h>
#include "config.h"
#include "LCD4Bits.h"
#include <stdio.h>
 
#define _XTAL_FREQ 8000000UL
 
#define DATA_PIN    RD0
#define DATA_DIR    TRISD0
 
uint8_t data[5];
void readDHT11(void){
    for(uint8_t i=0;i<5;i++) data[i]=0;  
    DATA_DIR=0;
    DATA_PIN=1;
    __delay_ms(10);
    DATA_PIN=0;
    __delay_ms(18);
    DATA_PIN=1;
    __delay_us(30);
    DATA_PIN=0;
    DATA_DIR=1;
    __delay_us(10);
    while(DATA_PIN==0);
    __delay_us(10);
    while(DATA_PIN==1);
    __delay_us(10);
 
    //Start of Transmission  
    for(uint8_t i=0;i<5;i++) {
        for(uint8_t j=0;j<8;j++){
        __delay_us(5);
        while(DATA_PIN==0);
        __delay_us(50);
        if(DATA_PIN==1) { data[i]|=(1<<7-j); while(DATA_PIN==1);}
    }
       __delay_us(10);
    }
    /*CRC Calculation - the last byte data[4] is check sum*/
    uint8_t crc = data[0]+data[1]+data[2]+data[3];
    if(crc!=data[4]) {for(uint8_t i=0;i<4;i++) data[i]=0; return;}
    __delay_us(10);
}
 
 
void main(void) {
    OSCCONbits.IRCF=7;
    char msg[8];
    PORTA=0;
    TRISA=0;
    lcdInit();
    lcdString("Temperature:");
    __delay_ms(1000);
    while(1){
        readDHT11();
        sprintf(msg,"%2dRH",data[0]);
        lcdXY(1,2); lcdString(msg);
        sprintf(msg,"%2d%cC",data[2],223);
        lcdXY(8,2); lcdString(msg);
        __delay_ms(500);
    }
    return;
}
 

I use its 8MHz internal oscillator clock source leaving the XTAL1 and XTAL2 pin opened.

Dashboard

Running Program

Running Program

 

Simulating Program

Proteus VSM can be used for circuit design and simulation. Click here to download its source file.

PIC16F84A Simple Frequency Meter With LCD Using XC8

Frequency meter can be made using a conventional digital ICs with a big size, and complicated circuit connection. A small 8-bit micro-controller could do this job using a low level Assembly language or even a higher level C language.

In this example, I use an 8-bit PIC16F84A micro-controller to count external TTL input pulse. The total count will update for every seconds.

Simulating Program

I use RA4/T0CKI (Timer0 External Clock Input) pin to count external TTL pulse. Since Timer0 is only 8-bit wide the maximum counting is only 255 counts. So I add Timer0 Interrupt to increase the maximum counts. I use XC8 built-in delay function to create a precise 1000 ms (1 second) delay before the summation of external pulse is evaluated. A 16x2 character LCD is suitable for this example.

#include <stdio.h>
#include <xc.h>
 
#define _XTAL_FREQ 4000000UL
 
#include "LCD4Bits.h"
 
void tmr0Init(void){
    PORTA=0;
    TRISA4=1;
    T0CS=1;
    T0SE=0;
    PSA=1;
    OPTION_REGbits.PS=0;
    T0IE=1;
    GIE=1;
    T0IF=0;
}
 
long TMR0H=0;
 
void interrupt T0_ISR(void){
    if(T0IF){
        TMR0H+=1;
        T0IF=0;
    }
}
 
int main(void){
    unsigned char freq[10];
    uint32_t temp=0;
    PORTB=0;
    TRISB=0;
    lcdInit();
    tmr0Init();
    lcdXY(4,1);
    lcdString("PIC16F84A");
    lcdXY(1,2);
    lcdString("Frequency Meter");
    __delay_ms(1000);
    lcdCommand(CLEAR_SCREEN);
    __delay_ms(5);
    lcdXY(4,1);
    lcdString("Frequency:");
    TMR0H=0;
    TMR0=0;
    while(1){
        __delay_ms(1000);
        temp=(TMR0H<<8)+TMR0;
        lcdXY(6,2);
        sprintf(freq,"%uHz ",temp);
        lcdString(freq);
        TMR0H=0;
        TMR0=0;
    }
    return 0;
} 

I can not test it on bread-board because this chip was burn out. And I only have some newer PIC chips. So this program can only be tested using a simulator like Proteus. We can use another PIC chip like the PIC16F628A, and CCS PICC compiler. 

Resource Usage

 

This program require 69.5% of program memory, and 89.7% of data memory. Click here to download this example.

 

Internal Oscillator of PIC18F1220

 

Introduction

Clock source of PIC18F1220 is driven from external source or internal source. Using external crystal, clocking frequency is broad but it needs additional clocking circuitry and components.

Oscillator type

External Crystal Oscillator

External clock source are Low Power (LP), Crystal/Resonator (XT), and High Speed (HS) crystal oscillator. Its frequency ranges from 32kHz to 20MHz.

Crystal oscillator and its capacitors value used

Internal RC Oscillator

Internal oscillator is an inside RC oscillator that can be set in program. Its frequency ranges from 31kHz to 8MHz. To use this feature, programmer need to work with PIC18F1220 configuration bits, Oscillator Control Register, and Oscillator Tuning Register.

Clock diagram of PIC18F1220

Using internal oscillator save components requirement, and on-board design space.

Setting Up in Program

Setting configuration bits of PIC18F1220 is a priority for internal oscillator.

Configuration Bits

There are up to 13 configuration registers in PIC18F1220. However CONFIGH1H (address 300001h) contains setting for internal oscillator.

CONFIG1H Configuration Register

However in XC8 programmer use “#pragma config” directive. Programmer can select only internal oscillator only, or with I/O function on RA6 and RA7.

Registers Setting

There are two registers in SFR relate to internal oscillator.

Oscillator Tuning Registers – OSCTUNE

This register make a frequency tuning of internal oscillator between its lowest frequency and its highest frequency.

Oscillator Tuning Registers – OSCTUNE

Oscillator Control Register – OSCCON

This register set system clock mode, switch between discrete frequency of internal oscillator, and status checking.

Oscillator Control Register – OSCCON

Programming Example

We want to test selected 4MHz internal oscillator. LED connects to RA7 blinks at a specific rate. A push button connects to RA0 toggles an output LED on RA6 whenever it’s pressed.

Schematic Diagram

Since internal oscillator is used, there is no requirement to add external crystal oscillator.

Schematic Diagram

C Programming

Port A is multiplexed with analog input function. User needs to disable this feature to make this port as a solely digital I/O.

C

/*

 * PIC18F1220 internal RC oscillator

 * and its I/O

 */

#include <xc.h>

#include "config.h"

​

#define _XTAL_FREQ  4000000

​

void main(void){

    /*Select 4MHz internal oscillator*/

    OSCCONbits.IRCF=0x06;

    /*Clear IO*/

    PORTA=0x00;

    LATA=0x00;

    /*Disable analog input function*/

    ADCON1=0x7F;

    /*RA0 digital input*/

    TRISA=0x01;

    while(1){

        RA7^=1;

        LATA6=RA0;

        __delay_ms(250);

    }

}

Configuration bits contain setting for this controller especially internal oscillator setting. We choose internal oscillator with I/O function on both RA6 and RA7.

C

// PIC18F1220 Configuration Bit Settings

​

// CONFIG1H

#pragma config OSC = INTIO2     // Oscillator Selection bits (Internal RC oscillator, port function on RA6 and port function on RA7)

#pragma config FSCM = ON        // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor enabled)

#pragma config IESO = ON        // Internal External Switchover bit (Internal External Switchover mode enabled)

​

// CONFIG2L

#pragma config PWRT = OFF       // Power-up Timer Enable bit (PWRT disabled)

#pragma config BOR = ON         // Brown-out Reset Enable bit (Brown-out Reset enabled)

// BORV = No Setting

​

// CONFIG2H

#pragma config WDT = OFF        // Watchdog Timer Enable bit (WDT disabled (control is placed on the SWDTEN bit))

#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

​

// CONFIG3H

#pragma config MCLRE = ON       // MCLR Pin Enable bit (MCLR pin enabled, RA5 input pin disabled)

​

// CONFIG4L

#pragma config STVR = ON        // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)

#pragma config LVP = ON         // Low-Voltage ICSP Enable bit (Low-Voltage ICSP enabled)

​

// CONFIG5L

#pragma config CP0 = OFF        // Code Protection bit (Block 0 (00200-0007FFh) not code-protected)

#pragma config CP1 = OFF        // Code Protection bit (Block 1 (000800-000FFFh) not code-protected)

​

// CONFIG5H

#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot Block (000000-0001FFh) not code-protected)

#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)

​

// CONFIG6L

#pragma config WRT0 = OFF       // Write Protection bit (Block 0 (00200-0007FFh) not write-protected)

#pragma config WRT1 = OFF       // Write Protection bit (Block 1 (000800-000FFFh) not write-protected)

​

// CONFIG6H

#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)

#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot Block (000000-0001FFh) not write-protected)

#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)

​

// CONFIG7L

#pragma config EBTR0 = OFF      // Table Read Protection bit (Block 0 (00200-0007FFh) not protected from table reads executed in other blocks)

#pragma config EBTR1 = OFF      // Table Read Protection bit (Block 1 (000800-000FFFh) not protected from table reads executed in other blocks)

​

// CONFIG7H

#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot Block (000000-0001FFh) not protected from table reads executed in other blocks)

​

Click here to download this programming example package.