Set the 'current LED' value for writePatternLine
        :param led_number: LED to adjust, 0=all, 1=LEDA, 2=LEDB

def setLedN(self, led_number=0):
        """Set the 'current LED' value for writePatternLine
        :param led_number: LED to adjust, 0=all, 1=LEDA, 2=LEDB
        """
        if ( self.dev == None ): return ''
        buf = [REPORT_ID, ord('l'), led_number, 0,0,0,0,0,0]
        self.write(buf)