51 MCU DHT11 temperature and humidity sensor

DHT11 is a temperature and humidity sensor with calibrated digital signal output. The accuracy is +-5%RH, the temperature is +-2℃, the range is 20-90%RH, and the temperature is 0~50℃.

1. Circuit connection analysis

1. Pin diagram

2. Wiring Diagram

The DHT11 device uses a simplified single bus communication. A single bus has only one data line, and the data exchange and control in the system are all completed by the single bus. The single bus usually requires an external pull-up resistor of about 5.1kΩ, so that when the bus is idle, its state is high. Since they are master-slave junctions, the slave can only respond when the host calls the slave. Therefore, the host must strictly follow the single bus sequence when accessing the device. If the sequence is confused, the device will not respond to the host.

2. Data Collection and Analysis

1. Total data timing

After the user host (MCU) sends a start signal, DHT11 switches from low power mode to high speed mode. After the host start signal ends, DHT11 sends a response signal, sends out 40-bit data, and triggers a signal collection.

2. The host sends a start signal

The I/O port of the microcontroller connected to the DATA pin of DHT11 outputs a low level, and the low level retention time cannot be less than 18ms, and then waits for DHT11 to make a response signal.

3. Detect the slave response signal

When the DATA pin of DHT11 detects a low level external signal, it waits for the low level of the external signal to end. After a delay, the DATA pin of DHT11 is in the output state, outputs a low level for 80 microseconds as a response signal, and then outputs a high level for 80 microseconds to notify the peripheral device to prepare to receive data.

4. Receive data

(1) Data judgment rules

The format of the bit data "0" is: 50 microseconds of low level and 26-28 microseconds of high level, and the format of the bit data "1" is: 50 microseconds of low level plus 70 microseconds of high level.

When receiving data, you can first wait for the low level to pass, that is, wait for the data line to be pulled high, and then delay for 60us, because 60us is greater than 28us and less than 70us, and then detect whether the data line is high at this time. If it is high, the data is judged to be 1, otherwise it is 0.

(2) Data format

40 bits of data are transmitted at a time, high bit first out

8-bit humidity integer data + 8-bit humidity decimal data + 8-bit temperature integer data + 8-bit temperature decimal data + 8-bit check bit.

(3) Data correction

Determine whether the result of "8-bit humidity integer data + 8-bit humidity decimal data + 8-bit temperature integer data + 8-bit temperature decimal data" is equal to the 8-bit check bit. If it is equal, the data is received correctly, otherwise the data should be discarded and received again.

3. Driver

#include

#include

#define uchar unsigned char

#define uint unsigned int

sbit Data=P3^6; //define data line

uchar rec_dat[9]; //Received data array for display

void DHT11_delay_us(uchar n)

{

    while(--n);

}

void DHT11_delay_ms(uint z)

{

   uint i,j;

   for(i=z;i>0;i--)

      for(j=110;j>0;j--);

}

void DHT11_start()

{

   Data=1;

   DHT11_delay_us(2);

   Data=0;

   DHT11_delay_ms(20); //delay more than 18ms

   Data=1;

   DHT11_delay_us(30);

}

uchar DHT11_rec_byte() //Receive a byte

{

   uchar i,dat=0;

  for(i=0;i<8;i++) //Receive 8 bits of data from high to low

   {          

      while(!Data); Wait for 50us low level to pass

      DHT11_delay_us(8); // Delay 60us, if it is still high, the data is 1, otherwise it is 0 

      dat<<=1; // Shift to receive 8-bit data correctly, shift directly when the data is 0

      if(Data==1) //When data is 1, add 1 to dat to receive data 1

         dat+=1;

      while(Data); //Wait for the data line to be pulled low    

    }  

    return dat;

}

void DHT11_receive() //Receive 40 bits of data

{

    uchar R_H,R_L,T_H,T_L,RH,RL,TH,TL,revise; 

    DHT11_start();

    if(Data==0)

    {

        while(Data==0); //Wait for high     

        DHT11_delay_us(40); //Delay 80us after pulling high

        R_H=DHT11_rec_byte(); //Receive high eight bits of humidity  

        R_L=DHT11_rec_byte(); //Receive the lower eight bits of humidity  

        T_H=DHT11_rec_byte(); //Receive high eight bits of temperature  

        T_L=DHT11_rec_byte(); //Receive the lower eight bits of temperature

        revise=DHT11_rec_byte(); //Receive correction bit

        DHT11_delay_us(25); //End

        if((R_H+R_L+T_H+T_L)==revise) //correction

        {

            RH=R_H;

            RL=R_L;

            TH=T_H;

            TL=T_L;

        } 

        /*Data processing, convenient display*/

        rec_dat[0]='0'+(RH/10);

        rec_dat[1]='0'+(RH%10);

        rec_dat[2]='R';

        rec_dat[3]='H';

        rec_dat[4]=' ';

        rec_dat[5]=' ';

        rec_dat[6]='0'+(TH/10);

        rec_dat[7]='0'+(TH%10);

        rec_dat[8]='C';

    }

}

/* LCD1602 is used here to display the collected data. The LCD1602 driver is explained in detail in the blogger's 51 microcontroller series blog*/

void main()

{

   uchar i;   

   lcd_init(); //lcd1602 initialization

   while(1)

   {   

       DHT11_delay_ms(1500); //After DHT11 is powered on, it needs to wait for 1S to get past the unstable state. No instructions can be sent during this period.

       DHT11_receive();

       lcd_write_command(0x80); //Start displaying from the first position of the first line of lcd1602

       for(i=0;i<9;i++)

       lcd_write_data(rec_dat[i]); //display data                      

   }

}