RaspberryPi Humidity and Temperature Sensor (obsolete)
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Schematics
Remember that the Pi revisions have different pinouts! This will work for Revison 2, that is board revision 0004[1]
Configure the Pi
Update the OS
This not necessary, but generally a good idea.
apt-get update apt-get ugrade
Install missing packages
If you have already installed them, you can skip this step.
apt-get install bc apt-get install gnuplot
Install DHT11 driver
Since there seems to be no kernel module, do this:
apt-get install git
git clone git://git.drogon.net/wiringPi cd wiringPi git pull origin cd wiringPi ./build
Create a file hum_temp.c with this content:
#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}; 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 checksum 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("Humidity: %d.%d%% Temperature: %d.%dC (%.1f *F)\n",dht11_val[0],dht11_val[1],dht11_val[2],dht11_val[3],farenheit); } else { printf("Invalid Data!!\n"); } } int main(void) { //printf("Interfacing Temperature and Humidity Sensor (DHT11) With Raspberry Pi\n"); if(wiringPiSetup()==-1) { exit(1); } dht11_read_val(); return 0; }
gcc -o sensor hum_temp.c -L/usr/local/lib -lwiringPi
./sensor Humidity: 46.0% Temperature: 22.0C (71.6 *F)
Code
This is how I read the device and generate a nice plot using GNUplot:
TBD
You might want to use a cronjob like this:
*/15 * * * * /home/pi/Development/temperature/readHumidityAndTemperature.sh > /dev/null 2>&1
Resulting graph
- More like this
- Links
- Where I got the ideas from:
- http://www.messtechniklabor.de/artikel-h0000-temperatur_und_luftfeuchtigkeit_messen.html
- http://www.tortosaforum.com/raspberrypi/dht11driver.htm
- http://www.frank-buss.de/raspberrypi/index.html
- http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/overview
- http://www.geeetech.com/wiki/index.php/Electric_thermometer_by_using_DHT11_sensor_module
- Where I learned to use xticks: http://psy.swansea.ac.uk/staff/carter/gnuplot/gnuplot_time.htm
- Nice to know: How to setup timezones: dpkg-reconfigure tzdata
- About various methods of connecting 1-wire devices: http://www.fhemwiki.de/wiki/Raspberry_Pi_und_1-Wire and http://blog.gegg.us/2013/03/4-different-methods-of-1-wire-access-on-raspberry-pi/
- Where this will be used: Tomat-O-Mat
- More about Raspberry Pi on this website
- Where I got the ideas from:
- Footnotes: