OpenHAB and OneWire

This article describes how to OpenHAB can read a Dallas DS18B20 temperature sensor directly attached to a Raspberry 3 GPIO, and the equivalent attached to the dedicated socket of the CM3-Home.

The DS18B20 sensor has this pinout:

It needs a 3.3V power supply and a 4.7 or 10KΩ resistor on the data line:

On the Raspberry PI3 connect the data line to PIN 7 (BCM 4) and add the lines below to /boot/config.txt file:

# Enable 1Wire on GPIO
dtoverlay=w1-gpio,gpiopin=4

On the CM3-Home connect the sensor as shown below:

As depicted on the schematic diagram, the 1-wire data line is interfaced through a dedicated buffer in order to allow a more robust bus, therefore it doesn't require a pullup.

add:

# Enable the 1-wire bus 
dtoverlay=w1-gpio,gpiopin=16

Reboot the board.

The sensors wired are automatically detected by the Linux Kernel and a new directory is created on the folder /sys/bus/w1/devices for each of them.

$ ls /sys/bus/w1/devices/
28-000006c423d3

In this case a temperature sensor with id=28-000006c423d3 has been detected. To read the temperature value type:

$ watch cat /sys/bus/w1/devices/28-000006c423d3/w1_slave 
a4 01 4b 46 7f ff 0c 10 da : crc=da YES
a4 01 4b 46 7f ff 0c 10 da t=26250

OpenHab

To read the sensor value we are going to use the binding that allows to execute periodically a script:

Install the Exec Binding

Scripts

Create the file

/etc/openhab2/script/onewiretemp.sh

add the following lines:

#!/bin/bash
wert=`cat /sys/bus/w1/devices/$1/w1_slave | tail -n1 | cut -d '=' -f2`
wert2=`echo "scale=3; $wert/1000" | bc`
echo $wert2

test the script executing the command ./onewiretemp.sh sensorID

Things

Create the file

/etc/openhab2/things/onewire.things

add the following line:

exec:command:onewiretemp1 [command="bash /etc/openhab2/scripts/onewiretemp.sh IDSensore", interval=60, timeout=5, autorun=false]

Items

Create the file

/etc/openhab2/items/onewire.items

add the following line:

String onewiretemp1Value "La temperatura del sensore 1 è [%s °C]" <temperature> {channel="exec:command:onewiretemp1:output"}

Add the sensor to sitemap to show the value on UI:

Text item=onewiretemp1Value

Or use the item value in a widget to show it in an habpanel, as in this example

Links

Massimiliano Casini (Coordinatore tecnico Service Assurance presso www.kenamobile.it)
Sono cresciuto nel modo IT di aziende ad alto contenuto tecnologico e da sempre ho acquisto esperienze nel settore della domotica e sicurezza residenziale. Negli ultimi dieci anni ho acquisito competenze specifiche nel campo delle TLC in particolare sulla rete GSM e sui protocolli ad essa collegati.
Sergio Tanzilli (Autore - Progettista hw & sw - Imprenditore - Musicista dilettante, classe 1964)
Fondatore di Area SX srl, Acme Systems srl e del TanzoLab, si occupa dal 1974 di elettronica digitale, dal 1978 di microprocessori, dal 1992 di microcontroller, dal 1995 di Linux e pubblicazioni su Web, dal 2005 di progettazione, produzione e commercializzazione di schede Linux Embedded.
http://www.tanzilli.com - http://www.acmesystems.it - https://github.com/tanzilli - sergio@tanzilli.com