Hello Duilio,
You should not only add a datasource to your dashboard but assign it to your chart, by selecting your datasource (it will be "DS_1" in your case) on the "Data Source" property in your chart properties. (caption "1" in the screenshot)
After that you should be able to select which type of chart you want to use in the "Chart Type" section (caption "2" in the screenshot)
Regards,
Nicolas