Controller with a transitional graphical user interface

FIG. 1 is a front view of a controller with a transitional graphical user interface flat control panel, showing the claimed design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof; and,

FIG. 4 is a fourth image thereof.

The broken lines illustrate the controller and form no part of the claimed design. The broken lines illustrate portions of the graphical user interface and form no part of the claimed design. The broken lines illustrate text and form no part of the claimed design. The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1 to 4 . The process or period in which one image transitions into another forms no part of the claimed design.