DHT11 is a temperature and humidity sensor with calibrated digital signal output . Its precision humidity is ±5%RH, temperature is ±2℃, measuring range humidity is 5~95%RH, and temperature is -20~+60℃.
The sensor contains a resistive humidity sensing element and an NTC temperature measurement device.
The three pins + and - are connected to VCC and GND respectively. The middle pin DATA is a data line through which a response signal can be sent to the sensor and 40-bit temperature and humidity data can be returned.
| Supply voltage | DC：3.3-5.5V |
|---|---|
| Working range (temperature) | -20~+60℃ |
| Measuring range (humidity) | 5~95%RH |
| Temperature accuracy | ±2℃ |
| Humidity accuracy | ±5%RH |
| Repeatability | Temperature: ±1℃; Humidity: ±1%RH |
| hysteresis(temperature) | ±0.3℃ |
| Hysteresis (humidity) | ±0.3%RH |
1. Wiring method:
2. Pin description
| pin | name | Comment |
|---|---|---|
| 1 | VDD | Power supply 3-5.5VDC |
| 2 | DATA | Serial data, single bus |
| 3 | NC | empty legs |
| 4 | GND | Ground, negative pole of power supply |
-
First, the Raspberry Pi pulls the data up and enters the idle state (IdleState).
-
Then pull the data line low for at least 18ms to notify DHT11 that it needs to collect data (Star MCU), and then give up control of the bus.
-
Then the data line will be pulled high by DHT11 (20-40us) , and then DHT11 will send a 80us low level and 80us high level data start signal to notify the Raspberry Pi to receive data.
-
Then a 40-bit 0,1 pulse signal will be sent
-
The 0 pulse includes 50us low level and 26us high level
-
And 1 pulse consists of 50us low level and 70us high level.
-
After the data is sent, the data bus is pulled high for a long time, and the bus enters idle mode again.
-
3. Raspberry Pi connection practice
Pin diagram
The pins selected for this connection are:
BCM18 ——>pi 12
VCC5V ——>pi 4
GND GND ——>pi 6
DHT11 connection:
Black wire - VCC - breadboard - pole
White wire - GND - breadboard + pole
Red line——DATA——Breadboard e port
Raspberry Pi connection
Black wire - VCC 5V - Raspberry Pi Pi4 - Breadboard - Extreme
White wire - GND GND - Raspberry Pi Pi6 - breadboard + pole
Purple line - BCM 18 - Raspberry Pi Pi12 - Breadboard port a
Raspberry Pi merged with DHT11
4. Test
Test code:
import RPi.GPIO as GPIO
import time
#温湿度
def delayMicrosecond(t): # 微秒级延时函数
start,end=0,0 # 声明变量
start=time.time() # 记录开始时间
t=(t-3)/1000000 # 将输入t的单位转换为秒，-3是时间补偿
while end-start<t: # 循环至时间差值大于或等于设定值时
end=time.time() # 记录结束时间
tmp=[] # 用来存放读取到的数据
data = 18 # DHT11的data引脚连接到的树莓派的GPIO引脚，使用BCM编号
a,b=0,0
def DHT11():
GPIO.setup(data, GPIO.OUT) # 设置GPIO口为输出模式
GPIO.output(data,GPIO.HIGH) # 设置GPIO输出高电平
delayMicrosecond(10*1000) # 延时10毫秒
GPIO.output(data,GPIO.LOW) # 设置GPIO输出低电平
delayMicrosecond(25*1000) # 延时25毫秒
GPIO.output(data,GPIO.HIGH) # 设置GPIO输出高电平
GPIO.setup(data, GPIO.IN) # 设置GPIO口为输入模式
a=time.time() # 记录循环开始时间
while GPIO.input(data): # 一直循环至输入为低电平
b=time.time() # 记录结束时间
if (b-a)>0.1: # 判断循环时间是否超过0.1秒，避免程序进入死循环卡死
break # 跳出循环
a=time.time()
while GPIO.input(data)==0: # 一直循环至输入为高电平
b=time.time()
if (b-a)>0.1:
break
a=time.time()
while GPIO.input(data): # 一直循环至输入为低电平
b=time.time()
if (b-a)>=0.1:
break
for i in range(40): # 循环40次，接收温湿度数据
a=time.time()
while GPIO.input(data)==0: #一直循环至输入为高电平
b=time.time()
if (b-a)>0.1:
break
delayMicrosecond(28) # 延时28微秒
if GPIO.input(data): # 超过28微秒后判断是否还处于高电平
tmp.append(1) # 记录接收到的bit为1
a=time.time()
while GPIO.input(data): # 一直循环至输入为低电平
b=time.time()
if (b-a)>0.1:
break
else:
tmp.append(0) # 记录接收到的bit为0
#while True循环输出
while True:
GPIO.setmode(GPIO.BCM) # 设置为BCM编号模式
GPIO.setwarnings(False)
del tmp[0:] # 删除列表
time.sleep(1) # 延时1秒
DHT11()
humidity_bit=tmp[0:8] # 分隔列表，第0到7位是湿度整数数据
humidity_point_bit=tmp[8:16]# 湿度小数
temperature_bit=tmp[16:24] # 温度整数
temperature_point_bit=tmp[24:32] # 温度小数
check_bit=tmp[32:40] # 校验数据
humidity_int=0
humidity_point=0
temperature_int=0
temperature_point=0
check=0
for i in range(8): # 二进制转换为十进制
humidity_int+=humidity_bit[i]*2**(7-i)
humidity_point+=humidity_point_bit[i]*2**(7-i)
temperature_int+=temperature_bit[i]*2**(7-i)
temperature_point+=temperature_point_bit[i]*2**(7-i)
check+=check_bit[i]*2**(7-i)
humidity=humidity_int+humidity_point/10
temperature=temperature_int+temperature_point/10
check_tmp=humidity_int+humidity_point+temperature_int+temperature_point
if check==check_tmp and temperature!=0 and temperature!=0: # 判断数据是否正常
print("Temperature is ", temperature,"C\nHumidity is ",humidity,"%")# 打印温湿度数据
a={"Temperature":temperature,"Humidity":humidity}
else:
print("error")
time.sleep(1)
GPIO.cleanup()Test Results:
