In this post we will see how to connect a DHT11 or DHT22 Temperature and Humidity sensor and configure RPi-Monitor to present and draw the outputs.
This article will also explain another capability of RPi-Monitor 2.x: the dual-axis.
Adafruit created a very good tutorial explaining how to use DHT11 or DHT22 . This tutorial is available at this address: http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/wiring.
Electronic assembly
This electronic assembly is quite simple and will need:
Software installation
Thanks to Adafruit ( again ;-) ) the installation is quite simple and can be done with two command lines.
Download Adafruit_DHT form Adafruit's github repository and copy is in /usr/bin as follow:
Warning: Be sure to use Linux linefeed format with line ending with LF (and not CR/LF like in Windows).
Let's now use this information and add humidity graphs on existing temperature graph.
We first have to extract the data. This is done like this:
As the unit are different than the one existing on the initial axis, we will add a second axis for the percentage of humidity. This is the purpose of the two last lines of the configuration bellow.
The first line is defining the usage of axis number 2 for the humidity.
The last line is defining how this graph should be drawn: On the right, starting from 0 up to 100.
graph_options can have other usefull option. They are described in the documentation of javascriptrrd.
After restarting RPi-Monotor with the command:
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Photo from Flickr    cc-by-nc-nd by Ham Hock |
Adafruit created a very good tutorial explaining how to use DHT11 or DHT22 . This tutorial is available at this address: http://learn.adafruit.com/dht-humidity-sensing-on-raspberry-pi-with-gdocs-logging/wiring.
Electronic assembly
This electronic assembly is quite simple and will need:
- 1 x DHT11 or 1 x DHT22
- 1 x 4.7k resistor
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| Schema extracted from Adafruit but using GPIO #27 instead of GPIO #4 |
Software installation
Thanks to Adafruit ( again ;-) ) the installation is quite simple and can be done with two command lines.
Download Adafruit_DHT form Adafruit's github repository and copy is in /usr/bin as follow:
wget http://goo.gl/oadpl -O Adafruit_DHT
sudo cp Adafruit_DHT /usr/bin/
To test the electronic assembly and the software installation execute the following command (for DHT11):
pi@raspberrypi~ $ sudo Adafruit_DHT 11 27
Using pin #17Data (40): 0x28 0x0 0x18 0x0 0x40
Temp = 24 *C, Hum = 40 %
You should see the information about temperature and humidity displayed as shown upper.
Note: The DHT11 and DHT22 sensors will only respond every second so if you are not getting data, be sure to wait few seconds before trying again.
Note: The DHT11 and DHT22 sensors will only respond every second so if you are not getting data, be sure to wait few seconds before trying again.
RPi-Monitor configuration
Warning: Be sure to use Linux linefeed format with line ending with LF (and not CR/LF like in Windows).
Let's now use this information and add humidity graphs on existing temperature graph.
We first have to extract the data. This is done like this:
As the unit are different than the one existing on the initial axis, we will add a second axis for the percentage of humidity. This is the purpose of the two last lines of the configuration bellow.
The first line is defining the usage of axis number 2 for the humidity.
The last line is defining how this graph should be drawn: On the right, starting from 0 up to 100.
graph_options can have other usefull option. They are described in the documentation of javascriptrrd.
After restarting RPi-Monotor with the command:
service rpimonitor restartYou will see a new curve in Temperature graph as shown in the screenshot bellow:
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| Graph with 2 Y axis: °C in left axis and % humidity (fixed from 0% to 100%) on right axis |