Wednesday, March 09, 2016

Raspberry Pi Temperature & Humidity Network Monitor

Picture of Raspberry Pi Temperature & Humidity Network Monitor
Please note that there's a Git repo for code at:
If you'd like the latest fixes or would like to contribute. Thanks Jonny Ervine!

I had some issues with Kingston SD Cards, but the SanDisk cards I'm using now have run for weeks without issues, so I'm changing the parts list to reflect that.
Also, after some 49 days, 16 hours, the display flatlines, as the reading routines start returning the same number over and over again. A reboot clears it, so just reboot once a month until I figure out what's up.

Over the past summer, my vacation home had a small water leak for three months, and I realized that had I been measuring the humidity in the effected area, I'd have
seen it go to 100% for a long time and I could have dispatched someone to fix the small problem before it became a big one.
And since I've been playing with Raspberry Pi computers for a while now, and saw an inexpensive temperature/humidity sensor on AdaFruit, I had all the pieces I needed
to implement an inexpensive network-connected monitor.
The Bill Of Materials (BOM):
1) Raspberry Pi Model B
2) Case
3) SD Card
4) Temperature/Humidity sensor
5 ) Power Supply (I use PoE splitters, but any 5V 1A Micro-USB supply will work)
I used the following exact parts, but obvious substitutions can be made to match local conditions and the state of your junk box. Shipping and the availability of bundles
may effect your final price.
$35.00 RPi
$ 8.12 Case (5.99 Euros)
$ 6.99 SD Card (Sandisk, not Kingston)
$15.00 Sensor
$15.99 PoE Splitter
And a few other miscellaneous things like hand tools, soldering iron, hot melt glue gun, small pieces of plastic wood, etc.

Step 1: Physical assembly

Picture of Physical assembly
Split the case, find the hardware bag inside, and set the rubber feet aside for later.

Attach the Raspberry Pi to the case bottom with the supplied hardware.

Remove the GPIO knockout with a razor blade or Xacto knife and snap the two case halves together.

To keep the power dissipation of the power supply and Raspberry Pi from effecting the sensor readings, I cut a piece of Azek plastic lumber about 1.1 x 2.4 x 0.75 inches as a standoff.

Heat up your hot-melt glue gun and stack the parts as in the picture. You'll have a few seconds to make the alignment perfect before the glue sets, so get the alignment close before you press the parts together.  Be careful not to use so much glue that it extrudes from the edges of the seams or extrudes into the case, where it might interfere with the SD card connector.

1) Glue the sensor to the standoff

2) Glue the standoff to the top half of the case. Be careful not to block the LED cutouts on the one side or the ribbon cable cutout for the camera on the other side.

3) Glue the case bottom to the top of the PoE adapter. Make sure the "LAN Out" connector is on the same side as the Raspberry Pi Ethernet adapter.

4) Stick the 4 rubber feet to the bottom of the power adapter.

5) Ensure the voltage-output selection switch is set to 5V. Put a dab of hot-melt glue in the switch to prevent it from being changed and destroying your Raspberry Pi.

Step 2: Electrical Assembly

Picture of Electrical Assembly
The White wire from the sensor is a spare ground, and is not needed.  Cut it off inside the sensor case, being careful not to cut any of the other wires.

Braid the other three wires to keep them together, and cut them off about 3.5 inches long.

Prepare a 5-pin single inline female connector (cut from or equivalent), and solder the wires to it:

1) Red (+3.3V)
2) No Connection
3) No Connection
4) Yellow (Data)
5) Black (Ground)

Plug the connector into the GPIO on the Raspberry Pi so that pin 1 on the connector (red wire) is on pin 1 of the GPIO connector (label P1 on the board, upper right in the picture).  Note that the Red wire is on GPIO Pin 1 (+3.3V), the Yellow wire is on GPIO pin 7 (GPIO 4), and the Black wire is on GPIO Pin 9 (Ground).

Tuck the excess wire into the case.

Use a short CAT5 cable (something like ) to connect the LAN OUT on the PoE splitter and the Raspberry Pi Ethernet jack.  Twist it up to make it stay close to the case.

Take the PoE output cable and a Micro-USB connector or cable and solder them together.  If using an AdaFruit Micro-USB connector, wire it up as shown at , if using a cut-off cable, determine +5 and Gnd wires with a multimeter.  Note that the TP-Link wire with the white stripe is POSITIVE.


Step 3: Raspberry Pi software setup

Picture of Raspberry Pi software setup
Getting the basic Raspberry Pi software up and running has been documented elsewhere, but basically, go to:
download the latest NOOBS (v1.3.2 as of this writing)
Format the SD card using the SD card tool at
Unzip the NOOBS file and put the contents at the root of the SD card.
Insert the SD card into the Raspberry Pi
Connect a keyboard, monitor, mouse, and LAN cable to the Raspberry Pi and connect the power supply (when you plug the PoE splitter into the LAN cable, the Raspberry Pi will power up).

Select the Raspian distribution and install it.
While that's installing, select English-US keyboard, which autoselects US Keymap

On first boot, the raspi-config utility will run.
Select Console Login as the default on boot
Change Locale to en_US UTF-8
Set timezone for your location
Set keyboard to Generic 105-key, English US
Enable the camera
change the hostname to something memorable (I used 'rpithon' for Raspberry Pi Temp/Humid On Net)
set 16M memory split as we'll be running headless
Enable SSH

Now you can either continue to use the console or ssh to it from another machine.  From my Mac I can just say:
ssh pi@rpithon
and log in using the password 'raspberry'.  If your router doesn't do the DNS to help you find 'rpithon' then make note of the IP address on the console and use that instead.

Update everything (this will take a while):

sudo apt-get update
sudo apt-get upgrade
sudo rpi-update

and reboot

Since this is going to be a LAN-only device, I get sick of playing "Mother May I?" with sudo, and I want to avoid any permissions problems with the additional software, so let's enable the root user and delete the pi user:

sudo passwd root
repeated twice

log back in as root user (or ssh root@rpithon) using the password selected above

remove pi user:

deluser -remove-home pi

I prefer Emacs, and don't want all the X-Windows stuff, so:

apt-get install emacs23-nox

Tell it to check the disk (SD Card) every time it boots:

tune2fs -c 1 /dev/mmcblk0p6

emacs /etc/ssh/sshd_config

change X11Forwarding to no
UseDNS no
ClientAliveInterval 60

service ssh restart

Step 4: Setting up LAMP server (web server)

Picture of Setting up LAMP server (web server)
So we want to be able to see the graphs we'll be generating (below), so we need to install a LAMP server.

LAMP: /Linux/Apache/MySQL/PHP&Perl

Linux is the operating system you are using (Raspian is a version of Debian, which is one of the common flavors of Linux)
Apache is the name of the web server software
MySQL is a SQL (Standard Query Language) database interface.  Databases sound really scary, but they are easy to use for simple things once you get used to them.
PHP and Perl are programming languages that are commonly used with websites, though we'll be using the Raspberry Pi standard Python for graphing the data and 'creating' the website.

apt-get install apache2  php5 mysql-client mysql-server vsftpd

This takes a while to install.  Midway through it'll ask you for a MySQL password, pick one memorable, I'll use 'password' for this tutorial.

Now you should be able to browse to http://rpithon (or http:// if the DNS doesn't work) and see a demo web page.  Try to edit /var/www/index.html and see if your changes show up when you refresh the webpage.

Step 5: ez_setup, MySQL, matplotlib

Picture of ez_setup, MySQL, matplotlib
ez_setup is a Python program that loads some nice addons (think of it as apt-get on steroids)


These next steps install some integration between Python and MySQL:

apt-get install python-mysqldb
apt-get install libmysqlclient-dev
easy_install MySQL-python

We'll be using the wonderful, powerful, and free(!) matplotlib for graphing our data, though we won't be using much of its power.

apt-get install libblas-dev liblapack-dev python-dev libatlas-base-dev gfortran python-setuptools python-scipy python-matplotlib

Step 6: WiringPi - GPIO interface

Picture of WiringPi - GPIO interface
Gordon Henderson has created a wonderful programming interface for the GPIO pins, including some drivers for the esoteric interface that our Temperature/Humidity sensor uses.  See for more details.

git clone git://
cd wiringPi
cd examples
emacs rht03.c (change the line #define RHT03_PIN 0 to #define RHT03_PIN 7 for the GPIO pin we're using)
make rht03
(you should get continuous temperature and humidity readings)

now we know our hardware is working, let's write our own program...

Step 7: Set up a database and a table

Picture of Set up a database and a table
So we have database software, but there's no database, or tables, so let's create them:

Open the MySQL command interface:

mysql -ppassword <-- br="" mysql="" password="" picked="" previously="" the="" you="">

Create a new database, called Monitoring

mysql> create database Monitoring;
Query OK, 1 row affected (0.00 sec)

Select that as our current database

mysql> use Monitoring;
Database changed

Create a single table in the database called TempHumid, which will contain the Unix Epoch (seconds since 1970) and Temperature and Humidity readings

mysql>create table TempHumid (ComputerTime INTEGER UNSIGNED,Temperature DECIMAL(5,1), Humidity DECIMAL(5,1));
Query OK, 0 rows affected (1.70 sec)

Done with MySQL, exit back to the command prompt.

mysql> exit

Step 8: Add readings to the database

Because the timing is tight on the sensor protocol, we're going to use C code to communicate with the sensor and add readings to the database.

So go to the root user's default directory:

cd ~

copy the Makefile (instructions on how to build the code we're going to create)

cp wiringPi/examples/Makefile .

emacs makeFile
change the two lines below to match this:

INCLUDE = -I/usr/local/include,/usr/include/mysql

LDFLAGS = -L/usr/local/lib,/usr/lib/arm-linux-gnueabihf -lmysqlclient -lpthread -lz -lm -lrt -ldl

Now copy th.c (included here) into your default directory. Change the password on line 68 from "password" to whatever you chose as the MySQL password.

When you compile it:

make th

you'll get a couple of warnings about declarations of exit, but it'll work fine.

Now you can run the program by typing:


It waits for a 60-second interval (minute) to end, then reads the sensor, inserts the time and sensor readings into the database, and loops forever.

Once we have that working properly, we want it to start whenever the Raspberry Pi starts up:

emacs /etc/rc.local

/root/th >> /root/th.log &

before the line that reads "exit 0"

reboot and see if th.log grows by one line per minute:

tail -f th.log

You can confirm that the data is getting into the database with:

mysql -ppassword
use Monitoring;
select * from TempHumid;

You should get a list of all values in the database.

Step 9: Graph data from the database

Picture of Graph data from the database
We're going to use Python for pulling readings out of the database and graph them with matplotlib.  Log in as root.

Set up the directory structure we'll be using:
mkdir Graph
cd Graph
mkdir graphics

copy into the Graph directory
Change the password on line 40:
DBconn = mdb.connect('localhost', 'root', 'password', 'Monitoring')
to match the MySQL password you set previously.
You can also set on line 81 to match your desired location name

Try running it:


It will get the last 24 hours of readings from the database, reorganize the data, throw out obvious bad data, create a graph of the results, and copy TH.png to /var/www so you should be able to see a new graph time you run  at http://rpithon/TH.png

Now we want this to run every minute, so:
export EDITOR=emacs
crontab -e
Add the line:
* * * * * /usr/bin/python /root/Graph/ >> /root/Graph/GraphTH.log
at the bottom of the file.

Now should run every minute, and if you update http://rpithon/TH.png (or http:///TH.png you should see it change about once a minute.

In the example above I covered the sensor with a damp Kleenex while it dried as a test.

Step 10: Monitor more than one location

Picture of Monitor more than one location
So I built five of these boxes for various locations, and on the LAMP server of one of them, added the following TH.html

    Temperature and Humidity readings




     Temperature and Humidity




  Sensor locations:


  White  - A Room

  Green  - Another Room

  Blue   - A Place To Monitor

  Purple - Another Place

  Orange - Somewhere Else


  Graphs are updated every minute.







so now I can point my browser at: http://rpithon-wht/TH and see all of the graphs updated every minute.

Step 11: Extras - Camera

Picture of Extras - Camera
You remember how we enabled the camera module when we installed the Raspian operating system?  Now we can add a Raspberry Pi Camera module:


Just feed the camera cable through the slot in the top case and plug it into the connector on the Raspberry Pi as per the instructions at using the connector next to the Ethernet port, with the tinned leads pointing away from the Ethernet connector.

I used another piece of Azek to position the camera with some hot melt glue, but there are obviously  a lot of options.

Now you can use the camera module to let you see into the area you are monitoring for temperature and humidity.  From another computer you can do something like:

ssh root@rpithon 'raspistill -o image.jpg'
scp root@rpithon:image.jpg .

Or have a cron job save a new file to the webserver on a regular basis!

In addition to the camera, there are lots of other peripherals and functions you can add to the Raspberry Pi, let your imagination guide you!

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