[51 microcontroller STC89C52] Use of DHT11 temperature and humidity sensor

1. Overview of DHT11

Data transfer logic

A complete data transmission of the module is 40 bits, with the high bit first

Data Format

8bit humidity integer data + 8bit humidity decimal data + 8bit temperature integer data + 8bit temperature decimal data + 8bit checksum

Communication process sequence diagram

2. Check whether the module exists

According to the following sequence diagram, perform communication initialization and check whether the module exists and whether the function is normal.

Sequential logic analysis

a : dht = 1

b ：dht = 0

Delay at least 18ms

c： dht = 1

Stuck point d: while(dht)

Card e point: while(!dht)

Stuck point f: while(dht)

 Code

void DHT11_Start()

{

dht = 1;

dht = 0;

//Delay 30ms

Delay30ms();

dht = 1;

    //Stuck point d: while(dht); stuck point e: while(!dht); stuck point f: while(dht)

while(dht);

while(!dht);

while(dht);

}

3. Read temperature and humidity data

Timing analysis of DHT11 transmitting 0

Timing analysis of DHT11 transmission 1

Code

char dates[5];

void Read_Data_From_DHT()

{

int i;//wheel

int j;//How many times to read in each round

char tmp;

char flag;

DHT11_Start();

for(i=0;i<5;i++){      

for(j=0;j<8;j++){

while(!dht);//Waiting for stuck g point

Delay40us();//Valid data are all high level, the duration is different, 40us reading, low level 0, high level 1

if(dht == 1){

flag = 1;

while(dht);

}else{

flag = 0;

} 

tmp = tmp << 1;

tmp |= flag;

}

datas[i] = tmp;

}

}

4. Serial port printing

#include "reg52.h"

#include "intrins.h"

sbit ledOne = P3^7;

sbit dht = P3^3;//The data of the module is inserted in p3.3

char dates[5];

sfr AUXR = 0x8E;

void UartInit(void) //9600bps@11.0592MHz

{

AUXR = 0x01;

SCON = 0x40; //Configure serial port working mode 1, REN disables reception

TMOD &= 0xF0;

TMOD |= 0x20; //Timer 1 working mode bit 8-bit automatic reloading

TH1 = 0xFD;

TL1 = 0xFD; //Initial value of 9600 baud rate

TR1 = 1;//Start the timer

}

void sendByte(char data_msg)

{

SBUF = data_msg;

while(!IF);

IF = 0;

}

void sendString(char* str)

{

while( *str != ''){

sendByte(*str);

str++;

}

}

void Delay30ms() //@11.0592MHz

{

unsigned char i, j;

i = 54;

j = 199;

do

{

while (--j);

} while (--i);

}

void Delay40us() //@11.0592MHz

{

unsigned char i;

_nop_();

i = 15;

while (--i);

}

void Delay1000ms() //@11.0592MHz

{

unsigned char i, j, k;

_nop_();

i = 8;

j = 1;

k = 243;

do

{

do

{

while (--k);

} while (--j);

} while (--i);

}

void DHT11_Start()

{

dht = 1;

dht = 0;

//Delay 30ms

Delay30ms();

dht = 1;

//Stuck point d: while(dht1); stuck point e: while(!dht); stuck point f: while(dht)

while(dht);

while(!dht);

while(dht);

}

void Read_Data_From_DHT()

{

int i;//wheel

int j;//How many times to read in each round

char tmp;

char flag;

DHT11_Start();

for(i= 0;i < 5;i++){

for(j=0;j<8;j++){

while(!dht);//Waiting for stuck g point

Delay40us();//Valid data are all high level, the duration is different, 40us reading, low level 0, high level 1

if(dht == 1){

flag = 1;

while(dht);

}else{

flag = 0;

} 

tmp = tmp << 1;

tmp |= flag;

}

datas[i] = tmp;

}

}

void main()

{

ledOne = 1;

UartInit();

Delay1000ms();

Delay1000ms();

while(1){

Delay1000ms();

Read_Data_From_DHT();

sendString("H:"); //Humidity

sendByte(datas[0]/10 + 0x30);

sendByte(datas[0]%10 + 0x30);

sendByte('.');

sendByte(datas[1]/10 + 0x30);

sendByte(datas[1]%10 + 0x30);

sendString("rn");

sendString("T:"); //Temperature

sendByte(datas[2]/10 + 0x30);

sendByte(datas[2]%10 + 0x30);

sendByte('.');

sendByte(datas[3]/10 + 0x30);

sendByte(datas[3]%10 + 0x30);

sendString("rn");

        //The decimal part of the humidity is 0; the decimal part of the temperature can only display 1 decimal digit, and the code needs to be modified.

}

}