DHT11.py

#!/usr/bin/python3
#-*- coding:utf-8 -*-
import RPi.GPIO as GPIO
import time

DHT11_DATA_LEN = 5

class DHT11(object):
	"""docstring for DHT11"""
	def __init__(self, datapin=24, powerpin=25):
		GPIO.setmode(GPIO.BOARD)
		self.pin = datapin
		GPIO.setwarnings(False)
		count=0

	def _read_data(self):
		self.data=[]
		# reset        
		GPIO.setup( self.pin , GPIO.OUT)
		GPIO.output( self.pin , GPIO.LOW)
		time.sleep(0.03) # 必须大于18ms
		GPIO.setup( self.pin , GPIO.IN)
		count=0
		while GPIO.input( self.pin ) == GPIO.HIGH:
			continue
		while GPIO.input( self.pin ) == GPIO.LOW:
			continue
		# 固定拉高80us，可用来做基准
		while GPIO.input( self.pin ) == GPIO.HIGH:
			count += 1
			continue
		base = count / 2
		# Get data
		while len(self.data)< DHT11_DATA_LEN*8:
			i = 0
			# 检测50us以上的低位
			while GPIO.input( self.pin ) == GPIO.LOW:
				continue
			# 此时电平为高，持续26-28us表示0，否则持续70us表示1
			while GPIO.input( self.pin ) == GPIO.HIGH:
				i += 1
				if i > 100: #防止死循环
					break
			if i < base:
				self.data.append(0)
			else:
				self.data.append(1)
		#print("DHT11 get data: ", self.data)


	def _cal(self):
		res=[]
		for i in range( DHT11_DATA_LEN ): # 5个数据分别为 湿度（整数，小数）；温度（整数，小数），校验
			res.append(0)
			for j in range(8):
				res[i] += self.data[i*8+j]<<(7-j)
		#print("DHT11 res: ", res)
		if res[0]+res[2]!=res[4]:  # 数据校验
			print("DHT11: data check error!")
			return -1, -1
		else:
		#    print("humidity: %d, temperature: %d C" %(res[0], res[2]))
			return res[0],res[2]

	def get(self):
		for i in range(5):
			self._read_data()
			(h, t)=self._cal()
			if h>0:
				break
			time.sleep(0.2) 
		return h,t

	def __exit__(self):
		GPIO.cleanup()