RaspberryPi Humidity and Temperature Sensor (obsolete)

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Schematics

RaspberryPiDHT11.png
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
#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.%d *C (%.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 = 45.0 % Temperature = 22.0 *C (71.6 *F)

Check setup

Check whether there is now our sensor device:

cd /sys/bus/w1/devices
ls -1
10-000802ad5087[2]
w1_bus_master1

See it's content (values):

cd 10-000802ad5087[3]
cat w1_slave
39 00 4b 46 ff ff 03 10 9c : crc=9c YES
39 00 4b 46 ff ff 03 10 9c t=28562[4]

Code

This is how I read the device and generate a nice plot using GNUplot:

#!/bin/bash
#set -x
#
# Script: readTemperature.sh
# Author: Heiko Kretschmer
# Purpose: Reading the temperature and generating a nice plot
#
#

#
# Globals
#
GDEVICEID="10-000802ad5087"
GDEVICESPATH="/sys/bus/w1/devices"
GDEVICEVALUEFILE="w1_slave"
GTIMESTAMPFORMAT="%Y-%m-%d_%H:%M"
GTIMESTAMP="`date +${GTIMESTAMPFORMAT}`"
GTIMESTAMPTIME="`date '+%H:%M'`"
GTIMESTAMPDATE="`date '+%Y-%m-%d'`" # ISO 8601 date format
GTIMESTAMPDATEHUMANREADABLE="`date '+%A, %Y-%m-%d'`"
GFOLDERBASE="/home/pi/Development/temperature"
GFOLDERLOGS="${GFOLDERBASE}/logs"
GFOLDERGRAPHS="${GFOLDERBASE}/graphs"
GFOLDERTMP="${GFOLDERBASE}/tmp"
GFILELOG="${GFOLDERLOGS}/readTemperature_${GTIMESTAMPDATE}.log"
GFILEGRAPH="${GFOLDERGRAPHS}/readTemperature_${GTIMESTAMPDATE}.svg"
GFILEPLOTCOMMANDS="${GFOLDERTMP}/readTemperature-plot.cmd"

#
# Main
#

# Init
test ! -d "${GFOLDERLOGS}" && mkdir "${GFOLDERLOGS}"
test ! -d "${GFOLDERGRAPHS}" && mkdir "${GFOLDERGRAPHS}"
test ! -d "${GFOLDERTMP}" && mkdir "${GFOLDERTMP}"

# Get the temperature
VALUERAW="`cat \"${GDEVICESPATH}/${GDEVICEID}/${GDEVICEVALUEFILE}\" | grep t= | cut -d= -f2`"
VALUE="`echo \"scale = 3; ${VALUERAW} / 1000\" | bc`"
#echo Temperature: ${VALUE}

# Write it into the log (one logfile per day to get nice graphs)
echo -e "${GTIMESTAMPTIME}\t${VALUE}" >> "${GFILELOG}"

# Generate the graph
test -f "${GFILEPLOTCOMMANDS}" && rm "${GFILEPLOTCOMMANDS}"
echo "reset" >> "${GFILEPLOTCOMMANDS}"
echo "set key inside right top vertical Right noreverse enhanced autotitles columnhead nobox" >> "${GFILEPLOTCOMMANDS}"

# Set time format for X axis
echo "set timefmt \"%H:%M\"" >> "${GFILEPLOTCOMMANDS}"
echo "set xdata time" >> "${GFILEPLOTCOMMANDS}"
echo "set format x \"%H:%M\"" >> "${GFILEPLOTCOMMANDS}"

# Setup line style (#1) for the temperature line
echo "set style line 1 lc rgb '#8b1a0e' pt 1 ps 1 lt 1 lw 2" >> "${GFILEPLOTCOMMANDS}" # http://www.gnuplotting.org/tag/grid/
echo "set style data lines" >> "${GFILEPLOTCOMMANDS}"

# Set X tics (one tic per hour, rotate that tick-labels by 90 deg and move em a bit)
echo "set xtics \"01:00\" rotate by 90 offset 0,-2 out nomirror" >> "${GFILEPLOTCOMMANDS}"

# Setup Grid (with line style #12)
echo "set style line 12 lc rgb '#E0E0E0' lt 0 lw 1" >> "${GFILEPLOTCOMMANDS}" # http://www.gnuplotting.org/tag/grid/
echo "set grid back ls 12" >> "${GFILEPLOTCOMMANDS}" # http://www.gnuplotting.org/tag/grid/

# Setup Title
echo "set title \"Temperature on ${GTIMESTAMPDATEHUMANREADABLE}\"" >> "${GFILEPLOTCOMMANDS}"

# Label X and Y Axis
echo "set ylabel \"°C\"" >> "${GFILEPLOTCOMMANDS}"
echo "set xlabel \"Time\" offset 0,-0.5" >> "${GFILEPLOTCOMMANDS}"

# Setup Y range
echo "set yrange [ 0.000 : ] noreverse nowriteback" >> "${GFILEPLOTCOMMANDS}"

# Set output file type to svg and plot it into file
echo "set term svg size 640,480" >> "${GFILEPLOTCOMMANDS}"
echo "set output \"${GFILEGRAPH}\"" >> "${GFILEPLOTCOMMANDS}"
echo "plot \"${GFILELOG}\" using 1:2 title 'Temperature' with l ls 1" >> "${GFILEPLOTCOMMANDS}"
cat "${GFILEPLOTCOMMANDS}" | gnuplot

You might want to use a cronjob like this:

*/15 * * * *    /home/pi/Development/temperature/readTemperature.sh > /dev/null 2&>1

Resulting graph

And this is how it looks:
RaspberryPiDHT11TemperaturePlotExample.svg
RaspberryPiDHT11HumidityPlotExample.svg


  1. Raspberry Board Revision Check
  2. This will differ, since this is the UID of my device.
  3. This will differ, since this is the UID of my device.
  4. This is the temperature in degrees celsius (multiplied by 1000), therefore I have 28.562°C in my living room. OMG! It's frickin' hot!