Pi3基础学习套件 Lesson17：DHT11温湿度模块

概述

在本课中，我们将学习如何驱动DHT11温湿度传感器模块。

所用器件

1 * Raspberry Pi

1 * Breadboard

1 * DHT11

Jumper wires

1 * T-Extension Board

1 * 40-Pin Cable

工作原理

DHT11是一款复合型数字温湿度传感器，包含校准过的温度和湿度输出信号。模块只有三个引脚：VCC、GND和DATA，这个模块采用单总线协议（OneWire protocol）进行通信，通信过程开始于DATA线向DHT11发送开始信号，DHT11接收信号并返回应答信号，然后主机接收应答信号并开始接收40位温湿度数据（8位湿度整数部分+ 8位湿度小数部分+ 8位温度整数部分+ 8位温度小数部分+ 8位校验和）。

                                                           DHT11

模块原理图如下

我们需要将DHT11接到Raspberry Pi的GPIO口上，具体连接如下图所示

实物接线

没画

软件

For C language users ,please take following steps:

1)  在/home/pi下新建一个.c源文件（文件名随意）

cd   ~

sudo  nano  dht11.c

2) 往新建的文件中写入一下代码

#include < wiringPi.h >
#include < stdio.h >
#include < stdlib.h >
#include < stdint.h >
#include < string.h >
#include < errno.h >

#define MAXTIMINGS  85
#define DHTPIN      15  //DHT connect to TxD
int dht11_dat[5] ={0,0,0,0,0};//store DHT11 data

void read_dht11_dat()
{
    uint8_t laststate = HIGH;
    uint8_t counter = 0;
    uint8_t j = 0,i;
    float f;//fahrenheit

    dht11_dat[0] = dht11_dat[1] = dht11_dat[2] = dht11_dat[3] = dht11_dat[4] = 0;

    //pull pin down to send start signal
    pinMode( DHTPIN, OUTPUT );
    digitalWrite( DHTPIN, LOW );
    delay( 18 );
    //pull pin up and wait for sensor response
    digitalWrite( DHTPIN, HIGH );
    delayMicroseconds( 40 );
    //prepare to read the pin
    pinMode( DHTPIN, INPUT );

    //detect change and read data
    for ( i = 0; i < MAXTIMINGS; i++ ) { counter = 0; while ( digitalRead( DHTPIN ) == laststate ) { counter++; delayMicroseconds( 1 ); if ( counter == 255 ) { break; } } laststate = digitalRead( DHTPIN ); if ( counter == 255 ) break; //ignore first 3 transitions if ( (i >= 4) && (i % 2 == 0) )
        {
            //shove each bit into the storage bytes
            dht11_dat[j / 8] <<= 1; if ( counter > 16 )
                dht11_dat[j / 8] |= 1;
            j++;
        }
    }
    //check we read 40 bits(8bit x 5) +verify checksum in the last byte
    //print it out if data is good
    if ( (j >= 40) &&
         (dht11_dat[4] == ( (dht11_dat[0] + dht11_dat[1] + dht11_dat[2] + dht11_dat[3]) & 0xFF) ) )
    {
        f = dht11_dat[2] * 9. / 5. + 32;
        printf( "Humidity = %d.%d %% Temperature = %d.%d C (%.1f F)\n",
            dht11_dat[0], dht11_dat[1], dht11_dat[2], dht11_dat[3], f );
    }
    else
    {
        printf( "Data not good, skip\n" );
    }
}


void print_info()
{
    printf("\n");
    printf("|***************************|\n");
    printf("|           DHT11 test      |\n");
    printf("| --------------------------|\n");
    printf("| DHT11 connect to GPIO14   |\n");
    printf("| --------------------------|\n");
    printf("|                     OSOYOO|\n");
    printf("|***************************|\n");
    printf("Program is running...\n");
    printf("Press Ctrl+C to end the program\n");
}


int main( void )
{
    if ( wiringPiSetup() == -1 )
    {
        fprintf(stderr,"Can't init wiringPi: %s\n",strerror(errno));
        exit(EXIT_FAILURE);
    }
    print_info();
    while ( 1 )
    {
        read_dht11_dat();
        delay(1000);//wait ls to refresh
    }

    return(0);
}

键盘输入Ctrl+X再按Y保存退出，完整的代码可以通过下面的命令获取

wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_17/dht11.c

3) 编译

gcc   -Wall   -o    dht11   dht11.c   -lwiringPi

4) 运行程序

sudo    ./dht11

5) 最终结果

运行上面的程序，屏幕上首先会输出DHT11如何与Pi连接等信息，然后不停打印温湿度值。

For Python Language users

1)  在/home/pi下新建一个.py脚本文件（文件名随意）

cd   ~

sudo  nano  dht11.py

2) 往新建的文件中写入一下代码

 import RPi.GPIO as GPIO
import time

#DHT11 connect to BCM_GPIO14
DHTPIN = 14

GPIO.setmode(GPIO.BCM)

MAX_UNCHANGE_COUNT = 100

STATE_INIT_PULL_DOWN = 1
STATE_INIT_PULL_UP = 2
STATE_DATA_FIRST_PULL_DOWN = 3
STATE_DATA_PULL_UP = 4
STATE_DATA_PULL_DOWN = 5

def read_dht11_dat():
    GPIO.setup(DHTPIN, GPIO.OUT)
    GPIO.output(DHTPIN, GPIO.HIGH)
    time.sleep(0.05)
    GPIO.output(DHTPIN, GPIO.LOW)
    time.sleep(0.02)
    GPIO.setup(DHTPIN, GPIO.IN, GPIO.PUD_UP)

    unchanged_count = 0
    last = -1
    data = []
    while True:
        current = GPIO.input(DHTPIN)
        data.append(current)
        if last != current:
            unchanged_count = 0
            last = current
        else:
            unchanged_count += 1
            if unchanged_count > MAX_UNCHANGE_COUNT:
                break

    state = STATE_INIT_PULL_DOWN

    lengths = []
    current_length = 0

    for current in data:
        current_length += 1

        if state == STATE_INIT_PULL_DOWN:
            if current == GPIO.LOW:
                state = STATE_INIT_PULL_UP
            else:
                continue
        if state == STATE_INIT_PULL_UP:
            if current == GPIO.HIGH:
                state = STATE_DATA_FIRST_PULL_DOWN
            else:
                continue
        if state == STATE_DATA_FIRST_PULL_DOWN:
            if current == GPIO.LOW:
                state = STATE_DATA_PULL_UP
            else:
                continue
        if state == STATE_DATA_PULL_UP:
            if current == GPIO.HIGH:
                current_length = 0
                state = STATE_DATA_PULL_DOWN
            else:
                continue
        if state == STATE_DATA_PULL_DOWN:
            if current == GPIO.LOW:
                lengths.append(current_length)
                state = STATE_DATA_PULL_UP
            else:
                continue
    if len(lengths) != 40:
        print "Data not good, skip"
        return False

    shortest_pull_up = min(lengths)
    longest_pull_up = max(lengths)
    halfway = (longest_pull_up + shortest_pull_up) / 2
    bits = []
    the_bytes = []
    byte = 0

    for length in lengths:
        bit = 0
        if length > halfway:
            bit = 1
        bits.append(bit)
    print "bits: %s, length: %d" % (bits, len(bits))
    for i in range(0, len(bits)):
        byte = byte << 1
        if (bits[i]):
            byte = byte | 1
        else:
            byte = byte | 0
        if ((i + 1) % 8 == 0):
            the_bytes.append(byte)
            byte = 0
    print the_bytes
    checksum = (the_bytes[0] + the_bytes[1] + the_bytes[2] + the_bytes[3]) & 0xFF
    if the_bytes[4] != checksum:
        print "Data not good, skip"
        return False

    return the_bytes[0], the_bytes[2]

def main():
    print "Raspberry Pi wiringPi DHT11 Temperature test program\n"
    while True:
        result = read_dht11_dat()
        if result:
            humidity, temperature = result
            print "humidity: %s %%,  Temperature: %s C" % (humidity, temperature)
        time.sleep(1)

def destroy():
    GPIO.cleanup()

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        destroy()

键盘输入Ctrl+X再按Y保存退出，完整的代码可以通过下面的命令获取

wget http://osoyoo.com/driver/pi3_start_learning_kit_lesson_17/dht11.py

3) 运行程序

sudo  python   ./dht11.py

4) 最终结果

运行上面的脚本程序，屏幕会不停打印温湿度值。