preemptively disconnect other existing EV3 objects

source/EV3.m

@@ -171,7 +171,16 @@ classdef EV3 < MaskedHandle
             %          brick.connect('usb', 'beep', 'on', );
             %
             % See also ISCONNECTED / :attr:`isConnected`
-
+            
+            % save variables of base directory in vars
+	    vars = evalin('base', 'whos');
+	    for k = 1:length(vars)
+		% if another EV3 object exists, preemptively disconnect it to prevent connection error
+		if strcmp(vars(k).class, 'EV3')
+		    evalin('base', [vars(k).name '.disconnect()'])
+		end
+	    end
+            
             if ev3.isConnected
                 if isCommInterfaceValid(ev3.commInterface)
                     % Warning lead to confusion of students. Since brick connection is still working