硬件准备
需要以下硬件:
传感器电路及原理
DHT11传感器外观
![](http://learn.adafruit.com/system/products/images/000/000/386/medium225/dht11_MED.jpg?1342023044)
参数
- 湿度测量范围:20%~90%RH(0-50℃温度补偿);
- 温度测量范围:0~+50℃;
- 湿度测量精度:±5.0%RH
- 温度测量精度:±2.0℃
- 响应时间:<5s;
电路图
DHT11一共4根引脚,左边第一根接电源5V (Pin 1),第二根为数据接口,接 Pin 7,第三根不接,第四根接地;在Pin 1和Pin7 之间还需要并联10K的电阻,以保持读数稳定。
![](http://learn.adafruit.com/system/assets/assets/000/001/860/original/dht11wiring.gif?1345831788)
安装好的样子:
![](http://ww3.sinaimg.cn/bmiddle/6bc40342jw1e2rx17tlckj.jpg)
读取温度和湿度的代码
数据读取流图:
![](http://1.bp.blogspot.com/-_sMwYSZMGLw/UJpY2RYIA9I/AAAAAAAAAS0/rJ9ZQwZ3IfM/s640/DHT11+timing+diagram.jpg)
#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#define MAX_TIME 85
#define DHT11PIN 7
int dht11_val[5]={0,0,0,0,0};
int errors=0;
void dht11_read_val()
{
uint8_t lststate=HIGH;
uint8_t counter=0;
uint8_t j=0,i;
float farenheit;
for(i=0;i<5;i++)
dht11_val[i]=0;
pinMode(DHT11PIN,OUTPUT);
digitalWrite(DHT11PIN,LOW);
delay(18);
digitalWrite(DHT11PIN,HIGH);
delayMicroseconds(40);
pinMode(DHT11PIN,INPUT);
for(i=0;i<MAX_TIME;i++)
{
counter=0;
while(digitalRead(DHT11PIN)==lststate){
counter++;
delayMicroseconds(1);
if(counter==255)
break;
}
lststate=digitalRead(DHT11PIN);
if(counter==255)
break;
// top 3 transistions are ignored
if((i>=4)&&(i%2==0)){
dht11_val[j/8]<<=1;
if(counter>16)
dht11_val[j/8]|=1;
j++;
}
}
// verify cheksum and print the verified data
if((j>=40)&&(dht11_val[4]==((dht11_val[0]+dht11_val[1]+dht11_val[2]+dht11_val[3])& 0xFF)))
{
//farenheit=dht11_val[2]*9./5.+32;
printf("%d.%d\t%d.%d\n", dht11_val[0],dht11_val[1],dht11_val[2],dht11_val[3]);
exit(1);
}
else {
errors = errors + 1;
if (errors > 5) {
printf("0.0\t0.0");
exit(2);
}
}
}
int main(void)
{
if(wiringPiSetup()==-1)
exit(1);
while(1)
{
dht11_read_val();
delay(3000);
}
return 0;
}
执行gcc sensor.c -o sensor -lwiringPi
,运行sensor
后输出:
root@raspberrypi2 /home/hugo/projects/dht11 # ./sensor
44.0 18.0
记录曲线图
这里我使用cosm.com的服务,注册申请好账号后,可以建立一个data feed和两个data stream,分别是温度和湿度,相应的Tag ID为1,和2,利用下来的脚本就可以上传数据了
#!/bin/bash
####################################################
LOCATION=<填你的程序路径> #home/hugo/projects/dht11
API_KEY='<填你的api_key>'
FEED_ID='<填你的feed_id>'
####################################################
COSM_URL=http://api.cosm.com/v2/feeds/$FEED_ID?timezone=+8
VAL=`$LOCATION/sensor`
t=`echo $VAL|awk '{print $2}'`
h=`echo $VAL|awk '{print $1}'`
STR=`awk 'BEGIN{printf "{\"datastreams\":[ {\"id\":\"1\",\"current_value\":\"%.1f\"}, {\"id\":\"2\",\"current_value\":\"%.1f\"} ] } ",'$t', '$h'}'`
echo $STR
echo $STR > $LOCATION/cosm.json
curl -v --request PUT --header "X-ApiKey: $API_KEY" --data-binary @$LOCATION/cosm.json $COSM_URL
然后可以使用如下格式的图片引用把曲线图嵌入任何网页:
<img src="https://api.cosm.com/v2/feeds/119331/datastreams/2.png?width=340&height=180&colour=%23f15a24&duration=2days&title=室内湿度&show_axis_labels=false&detailed_grid=true&scale=&timezone=8"/>
下面是我的曲线图:
![](https://api.cosm.com/v2/feeds/119331/datastreams/2.png?width=340&height=180&colour=%23f15a24&duration=2days&title=室内湿度&show_axis_labels=false&detailed_grid=true&scale=&timezone=8)
![](https://api.cosm.com/v2/feeds/119331/datastreams/1.png?width=340&height=180&colour=%23f15a24&duration=2days&title=室内温度&show_axis_labels=false&detailed_grid=true&scale=&timezone=8)
参考
- http://www.rpiblog.com/2012/11/interfacing-temperature-and-humidity.html
- http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/wiring