Struggling with Serial Binding and Regular Expressions


I am new to Openhab and I try to establish a bidirectional serial communication between a raspberry pi 3 B+ and an Arduino (a Mega 2560). I am running Openhab 2.3 on the raspberry pi.

After some initial problems I am able to send commands to the Arduino, but until now I failed to interpret the response of the Ardiuno:

e.g.: The Arduino receives a simple “4”, turns on a valve and responds with “Valve 1 ON”.
I am able to read the serial string send by the Arduino and display it on my UI with the item

String Feedback “RS232” { serial="/dev/ttyUSB0@9600"}
and the sitemap element
Text item=Feedback label=“RS232 [%s]”

This works fine (except the additional “)” which is sent by the serial binding (cp. Serial Binding sends close bracket after update to 2.3

I then tried to filter the serial feedback with regular expressions for specific strings and that´s where I am struggling at the moment: None of the REGEX definitions I wrote seem to work. I even copied the first example from the documentation (

My item is defined as:
String Pos12 “Pos12Test” { serial="/dev/ttyUSB0@9600,REGEX(Position:([0-9.]*))"}
in my sitemap I use
Text item=Pos12 label=“Pos12Test [%s]”

On the Arduino I use the command:
Serial.println(“Position:12”); (tried it with Serial.print(“Position:12”) as well)

While the item
Text item=Feedback label=“RS232 [%s]”
displays “Position 12” correctly I don´t see anything on the item with the regular expression.

In the log files I found this error:

ERROR] [ui.internal.items.ItemUIRegistryImpl] - Cannot retrieve item for widget org.eclipse.smarthome.model.sitemap.Text
ERROR] [ui.internal.items.ItemUIRegistryImpl] - Cannot retrieve item ‘Pos12’ for widget org.eclipse.smarthome.model.sitemap.Text

Can someone please point me in the right direction?