def _get_fb_device(self):
        """
        Internal. Finds the correct frame buffer device for the sense HAT
        and returns its /dev name.
        """

        device = None

        for fb in glob.glob('/sys/class/graphics/fb*'):
            name_file = os.path.join(fb, 'name')
            if os.path.isfile(name_file):
                with open(name_file, 'r') as f:
                    name = f.read()
                if name.strip() == self.SENSE_HAT_FB_NAME:
                    fb_device = fb.replace(os.path.dirname(fb), '/dev')
                    if os.path.exists(fb_device):
                        device = fb_device
                        break

        return device
Internal. Finds the correct frame buffer device for the sense HAT
        and returns its /dev name.