Overview of DHT11
DHT11 is a single wire digital humidity and temperature sensor, which provides humidity and temperature values serially.
It can measure the relative humidity in perce
It has 4 pins of which 2 pins are used for supply, 1 is not used and the last one is used for data.
The data is the only pin used for communication. Pulses of different TON and TOFF are decoded as logic 1 or logic 0 or start pulse or end of a frame.
For more information about the DHT11 sensor and how to use it, refer to the topic DHT11 sensor in the sensors and modules topic.
DHT11 Temperature and Humidity Sensor
Connection Diagram of DHT11 to PIC18F4550
DHT11 Interfacing with PIC18F4550
The above circuit diagram shows the interfacing of PIC18F4550 with the DHT11 sensor.
In that, a DHT11 sensor is connected to RA0 (PORTA).
Programming Steps
First, initialize the LCD16x2_8-bit library.
Define pin no. to interface DHT11 sensor, in our program we define RA0 (Pin no.2)
Send the start pulse to the DHT11 sensor by making low to high on the data pin.
Receive the response pulse from the DHT11 sensor.
After receiving the response, receive 40-bit data serially from the DHT11 sensor.
Display this received data on LCD16x2 along with error indication.
DHT11 Code for PIC18F4550
/*
* DHT11 Interfacing with PIC18F4550
* http://www.electronicwings.com
*/
#include <pic18f4550.h>
#include <xc.h>
#include <stdio.h>
#include "Configuration_Header_File.h"
#include "LCD_16x2_8-bit_Header_File.h"
#define Data_Out LATA0 /* assign Port pin for data*/
#define Data_In PORTAbits.RA0 /* read data from Port pin*/
#define Data_Dir TRISAbits.RA0 /* Port direction */
#define _XTAL_FREQ 8000000 /* define _XTAL_FREQ for using internal delay */
void DHT11_Start();
void DHT11_CheckResponse();
char DHT11_ReadData();
void main()
{
char RH_Decimal,RH_Integral,T_Decimal,T_Integral;
char Checksum;
char value[10];
OSCCON = 0x72; /* set internal oscillator with frequency 8 MHz*/
LCD_Init(); /* initialize LCD16x2 */
ADCON1=0x0F; /* this makes all pins as a digital I/O pins */
while(1)
{
DHT11_Start(); /* send start pulse to DHT11 module */
DHT11_CheckResponse(); /* wait for response from DHT11 module */
/* read 40-bit data from DHT11 module */
RH_Integral = DHT11_ReadData(); /* read Relative Humidity's integral value */
RH_Decimal = DHT11_ReadData(); /* read Relative Humidity's decimal value */
T_Integral = DHT11_ReadData(); /* read Temperature's integral value */
T_Decimal = DHT11_ReadData(); /* read Relative Temperature's decimal value */
Checksum = DHT11_ReadData(); /* read 8-bit checksum value */
/* convert humidity value to ascii and send it to display*/
sprintf(value,"%d",RH_Integral);
LCD_String_xy(0,0,value);
sprintf(value,".%d ",RH_Decimal);
LCD_String(value);
LCD_Char('%');
/* convert temperature value to ascii and send it to display*/
sprintf(value,"%d",T_Integral);
LCD_String_xy(1,0,value);
sprintf(value,".%d",T_Decimal);
LCD_String(value);
LCD_Char(0xdf);
LCD_Char('C');
sprintf(value,"%d ",Checksum);
LCD_String_xy(1,8,value);
/* check addition of humidity and temperature value equals to checksum */
if(Checksum != (RH_Integral + RH_Decimal + T_Integral + T_Decimal))
LCD_String_xy(0,8,"Error");
else
LCD_String_xy(0,8,"No Error");
MSdelay(500);
}
}
char DHT11_ReadData()
{
char i,data = 0;
for(i=0;i<8;i++)
{
while(!(Data_In & 1)); /* wait till 0 pulse, this is start of data pulse */
__delay_us(30);
if(Data_In & 1) /* check whether data is 1 or 0 */
data = ((data<<1) | 1);
else
data = (data<<1);
while(Data_In & 1);
}
return data;
}
void DHT11_Start()
{
Data_Dir = 0; /* set as output port */
Data_Out = 0; /* send low pulse of min. 18 ms width */
__delay_ms(18);
Data_Out = 1; /* pull data bus high */
__delay_us(20);
Data_Dir = 1; /* set as input port */
}
void DHT11_CheckResponse()
{
while(Data_In & 1); /* wait till bus is High */
while(!(Data_In & 1)); /* wait till bus is Low */
while(Data_In & 1); /* wait till bus is High */
}
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