Design of temperature and humidity LabView host computer monitoring system based on single chip DHT22

1. System plan
This design uses AT89C52 microcontroller as the main controller. The LCD 1602 displays the temperature and humidity. LabView communicates with the host computer. The host computer displays the temperature. At the same time, the host computer can set the upper and lower temperature limits. When the measured temperature is lower than or higher than the upper limit, the temperature Alarm, the upper computer can control the starting and shutting down of the heating equipment of the lower computer, and realize the exchange of data between the upper computer and the lower computer.

2. The hardware design
schematic diagram is as follows:

3. Microcontroller software design
1. The microcontroller code is mainly serial port initialization and serial port interrupt service routine. The first is the serial port initialization:
void uart_init()
{
TMOD |= 0x20;//Timer 1, working mode 2 8-bit automatic reloading
TH1 = 0xfd;
TL1 = 0xfd; //Set the bit rate 9600
SM0 = 0;
SM1 = 1 ;//Serial port working mode 1, 8-bit UART baud rate variable
TR1 = 1; //Start timer 1
REN = 1;
EA = 1; //Open total interrupt
ES = 1; //Open serial port interrupt
}
2 , paste the two functions of the 51 microcontroller responsible for serial port transmission:
void SendByte(unsigned char dat) //Send one byte of data, the formal parameter dat is the data to be sent.
{
SBUF = dat; //Write data to the serial port buffer
while(!TI); //Wait for the sending to complete
TI = 0;
}
void SendArray(unsigned char *Array, unsigned char Size)//Send an array through the serial port, Construct a for loop, change the index and send
{
unsigned char i;

for(i = 0; i < Size; i++)
{
SendByte(Array[i]);
}
}
Process the received data in the serial port interrupt:
void uart(void ) interrupt 4 //Serial port interrupt
{
unsigned char Res;
static unsigned char Rec_state = 0;

if(RI) //Data received
{
RI = 0; // Clear interrupt request
Res = SBUF;
if(Res == 0xFF) // Frame header received
{
Rec_state = 1;
}
else if(Rec_state == 1 && Res == 0xEE)//Received end of frame
{
Rec_state = 0;
}
else if(Rec_state == 1)
{
switch(Res)//Received data, relay control
{
case 0x02: RY2 = 0; break;
case 0x03 : RY2 = 1; break;
default : RY2 =1; break;
}
}
}
else //After sending one byte of data
{
//TI = 0;
}
}
3. Paste the DHT22 temperature and humidity reading function
unsigned char Read_Sensor(void )
{
unsigned char i;
//Host pulls low (Min=800US Max=20Ms)
DHT_PIN = 0;
Delay_N1ms(18); //Delay 18Ms

//Release bus delay (Min=30us Max=50us)
DHT_PIN = 1;
Delay_N10us(2); //Delay 30us
//The host is set to input the sensor response signal
DHT_PIN = 1;

Sensor_AnswerFlag = 0; // Sensor response flag

//Judge whether the slave has a low-level response signal. If it does not respond, it will jump out. If it responds, it will run downward
if(DHT_PIN ==0)
{
Sensor_AnswerFlag = 1; //Receive the start signal
Sys_CNT = 0;
//Judge the slave. Whether the machine sends out a low-level response signal of 80us and ends
while((!DHT_PIN))
{
if(++Sys_CNT>300) //Prevent entering an infinite loop
{
Sensor_ErrorFlag = 1;
return 0;
}
}
Sys_CNT = 0;
// Determine whether the slave sends a high level of 80us. If it does, it will enter the data receiving state
while((DHT_PIN))
{
if(++Sys_CNT>300) //Prevent entering an infinite loop
{
Sensor_ErrorFlag = 1;
return 0;
}
}
/ / The data receiving sensor sends a total of 40 bits of data
// That is, the high bits of 5 bytes are sent first and the 5 bytes are the high bits of humidity, the low bits of humidity, the high bits of temperature, the low bits of temperature, checksum
// The checksum is: high bits of humidity + low bits of humidity + temperature High bit + temperature low bit
for(i=0;i<5;i++)
{
Sensor_Data[i] = Read_SensorData();
}
}
else
{
Sensor_AnswerFlag = 0; // Sensor response not received
}
return 1;
}
4. Host computer The software design
host computer is developed with the help of LabView. The interface is relatively simple. First, the UI interface is designed on the front panel, and then the software development is completed through graphical programming on the back panel. Here is a screenshot of the front panel of the host computer:

The screenshot of the rear panel is as follows: