I have been playing a bit with an Arduino Yun. I am using a HTU21D Temperature and Humidity sensor and the Thingworx C-Sdk to send data to the Thingworx Server. Unfortunately, I don't have any documentation available yet. Depending on your Arduino Capabilities, the easiest way to send data from it into Thingworx would be through REST API calls like for example :
Where 10.132.36.68:8080 is the IP address of your Thingworx instance. You can use also the name of the instance (e.g. thingworx-academic-staff.ptcmscloud.com).
RPISensor2 is the name of the Thing created on the Thingworx instance for which you want to set a property value (Note that you need to use a Generic Thing as template to be able to set its properties using REST calls).Temp is the property name.
So in the example above I am setting the value 85 to the Temp Property of the RPISensor2 Thing created on the Thingworx instance located at this ip address : 10.132.36.68:8080.You can replace the 85 value with a value read from a sensor and then use this URL to make a HTTP request from an Arduino Sketch.
If your Arduino has more processing capabilities like the Arduino Yun, you can try using the Thingworx C-SDK. There is an example explaining how to use it to send data into Thingworx.