Raspberry Pi

All posts tagged Raspberry Pi

OpenHAB is one of the most promising home automation solutions I have seen in years. It offers an open-source, vendor-agnostic, and cloudless solution to home automation (though a cloud service is available). The ability to integrate hardware and software from a large number of existing manufacturers, and other open-source projects, is perhaps it’s most valuable characteristic.

Many of the embedded hardware products dijit has developed and implemented can easily be integrated into OpenHAB.

This week, hack local (the hackerspace R&D arm of dijit) began testing various setups using products on hand. The first project involved setting up an openHAB instance on an O.G. Raspberry Pi model B, using the onboard GPIO for Maxim 1-Wire DS18b20 temperature sensors.

The goals of this project:

  • Stand up a functioning openHAB instance on a Raspberry Pi B.
  • Create a 1-wire network of temp sensors using a star topology.
  • Read multiple 1-wire temps from a single Raspberry Pi GPIO pin.
  • Develop hardware for a modular and “plug-and-play” solution based on this project.

Here is how we fared:

Step 1: Install and configure openHABianPi

To streamline installation of openHAB on the Pi, a custom distro ‘openHABian’ is offered here: https://community.openhab.org/t/openhabian-hassle-free-rpi-image/13379

The tag line reads: “Flash, plug, wait, enjoy”, and quite honestly that is exactly what our results were.

Download img file, flash to SD card, boot up Pi, wait approximately 45min, and we were off.

If our only objective were to have a running instance of openHAB on a Raspi, we would have been marking the project complete within the hour and enjoying beverages the rest of the evening. But alas, there was much work yet to be done. We now had a working openHAB with SSH access and many web UI’s to choose from:

Step 2: Build 1-wire sensor network

The first challenge was to stop referring to the sensors as Dallas 1-Wire, as Maxim Integrated bought out Dallas Semiconductor….oh…about 16 years ago. Anyway, with a handful of some Maxim DS18b20 temperature sensors, a spool of Cat-5, and a network topology map that appears to be written by a school kid (pulled right from the official Maxim website), we set out to build a hard-wired sensor network:

Because the temp sensors would be in separate rooms, and on 3 different floors, we opted for the star topology. We followed Maxims guidelines on the radius (distance from master to farthest node) and weight of the network, to reduce reflections and maximize timing. This will be important as we expand our 1-wire sensor network and add devices (contacts, switches, and iButtons).

From here, we connected our 1-wire sensor network to GPIO pin 4 on the RasPi. Below is our original breadboard testing version of the connection:

Note the 4.7k pull-up resistor. Only one of these is required in total (not each sensor).

Step 3: Reading Temperature sensors through GPIO on RasPi

After the physical sensor network was in place, we then began testing out the openHAB binding for 1-wire, which looked very promising. Unfortunately, this binding is designed to be used in cooperation with ow-server, a software package which facilitates 1-wire communication in linux. Unfortunately, the hardware connection to sensors for ow-server is limited to serial, USB, or network sockets/tcp. There is no current configuration for GPIO sensors that we could find.

Not to be deterred, and not wanting to re-invent the wheel, we were able to track down a RasPi GPIO implementation on a German blog here: http://www.itbasic.de/openhab-onewire-sensoren-einbinden/

This method utilizes the Exec Binding in openHAB, and runs a script to poll the sensors and format the output. We modified the script to get output values from our temperature settings in ‘Murican, otherwise known as Fahrenheit. Ironically, Fahrenheit was a Dutch-German….but, I digress… Here is our modified script:

wert=`cat /sys/bus/w1/devices/$1/w1_slave | tail -n1 | cut -d '=' -f2`
wert2=`echo "scale=3; $wert/1000 * 9.0 / 5.0 + 32.0" | bc`
echo $wert2

The next step was to get the RasPi to communicate with our temp sensor network and implement this script within openHAB.

The latest RasPi kernels have built-in driver support for 1-wire, using dtoverlays in /boot/config.txt. We leveraged this by adding the following line to our Pi’s config.txt:


After a reboot, we confirmed the RasPi could see our temp sensors by heading here :

$ cd /sys/bus/w1/devices

If the w1 directory does not exist, the 1-wire driver was not loaded, and config.txt is likely to blame. Note that the config.txt that comes with openHABian contains 3 sections for the various version of RasPi’s: 1, 2, and 3, so the correct section must be modified for the corresponding RasPi version.

The 1-wire temp sensors each have a UID (28-xxxxxxxxxxxx) that is displayed in this folder. This UID is used to poll each sensor in the script:

$ onewiretemp.sh 28-xxxxxxxxxxxx

We placed the script in the appropriate folder for openHAB at ‘/etc/openhab2/scripts’. Manually running the script confirms our sensors are communicating with the RasPi and our syntax is correct:

pi@openHABianPi:/etc/openhab2/scripts$ sudo bash ./onewiretemp.sh 28-xxxxxxxxxxxx

Step 4: Creating the openHAB items, things, sitemap, etc.

After confirming all temp sensors were reporting in terminal using the script, we then installed the Exec Binding, and created the appropriate openHAB files for our things.

In openHAB’s Paper UI (http://192.168.blah.blah:8080/paperui/index.html), the Exec Binding can be installed by navigating to:

Add-ons>Bindings>Exec Binding


Once the binding was installed, we then created our custom files for the temp sensor readings:


exec:command:onewiretemp1 [command="bash /etc/openhab2/scripts/onewiretemp.sh 28-xxxxxxxxxxxx"]
exec:command:onewiretemp2 [command="bash /etc/openhab2/scripts/onewiretemp.sh 28-xxxxxxxxxxxx"]
exec:command:onewiretemp3 [command="bash /etc/openhab2/scripts/onewiretemp.sh 28-xxxxxxxxxxxx"]


String onewiretemp1Value "Temp 1 is [%s °F]" {channel="exec:command:onewiretemp1:output"}
String onewiretemp2Value "Temp 2 is [%s °F]" {channel="exec:command:onewiretemp2:output"}
String onewiretemp3Value "Temp 3 is [%s °F]" {channel="exec:command:onewiretemp3:output"}

It is important that you specify “output” for the channel that links the item to the thing. Other value options will not work with this ‘script method’ we have chosen.
And finally, some sample sitemap entries:

Frame label="Environment" {

Text label=”Temperatures” icon=”temperature_hot” {
Text item=onewiretemp1Value
Text item=onewiretemp2Value
Text item=onewiretemp3Value
Text label=”Temp Charts” icon=”line-incline” {
Chart item=onewiretemp1Value period=d refresh=300
Chart item=onewiretemp2Value period=d refresh=300

We are still playing around with the chart features, and displaying a color which represents the value of the temperature sensor (i.e. if temp is equal to or below 65 color is blue, over 70 is orange, over 80 is red, etc.).

Step 5: Testing the UI display

Testing with openHAB’s Basic UI demonstrates that we now have a fully functioning temperature sensor network, displaying live temps from 3 levels of our test house:

…it’s cold here in the winter….


That’s it! There will be lots more to come on openHAB hardware setups such as this, so stay tuned.

Next steps and product ideas:

We are taking the lessons we learned from this project and creating a modular 1-wire hardware setup using rj-45 connectors, patch cables, etc., to simplify the physical connections from 1-wire sensor to openHAB hardware such as the RasPi. The goal will be to provide a “plug and play” hardware solution to compliment the amazing openHAB software.

We are excited to announce that the first kit available in the store will be a Raspberry Pi XBMC media center kit! This kit will include everything needed to mount a Raspberry Pi to any VESA compatible TV for a compact and seamless media center solution. Features of the kit include relocating the Raspi’s ports, drawing power from the TV USB port, and most importantly the entire kit will be released as open-source. Our mission here at dijit is to give you the tools to make technology work for you. The parts list, software, 3D printing files, and instructions for this kit will all be available for download. Our wiki will provide the specifics, and the support forum will include installation and troubleshooting help. We expect kits to be in stock by the end of the month!