I am sensing a bit of confusion with regards to some of the platform's constructs. Widgets and data sources are two very different concepts that exist in two different applications. The Portals application that Exosite provides is an example application that provides a quick environment in which to get started with IoT development, and provide data visualization through our dashboard builder and widgets. Data sources are a back-end object that holds time-series data in Time:Value pairs. You are in-fact interacting with a couple of layered applications while logged into Portals.
I should also be clear that you do not have to use Portals when you engage with Exosite. Our platform is application agnostic, and Portals is provided for free as an accelerant.
Here is a link to an article of ours that explains the high-level structure of our platform: https://support.exosite.com/hc/en-us/articles/200491553-One-Platform-101
Let us know if helps clear things up.
To answer your question: "No, there is not a standard widget that will do what you are looking for". The closest is the on/off widget, that is 'writing' either a 1 or 0 to a data source. However this functionality can be built into a custom widget, and you can leverage the examples posted above to create this.
I would recommend steering away from using the widget to contain the communication and storage logic. Using the widget as a end-user interface to write data will stay in-line with widget strengths. You can continue to use the data source as the repository for your data, the container in which your widget will write into, and the object that your device will poll.
Some supplementary reading about the constructs mentioned above:
Let us know how this works out for you tomorrow -- We are always happy to help,